Publisher：Physics of Plasmas  

We investigated the mass dependency of the high-wavenumber turbulence, which occurs at scales smaller than the ion effective Larmor radius, in a partially magnetized plasma column. In this system, two different types of fluctuations were observed: one exhibiting a coherent discrete spectrum, while the other displaying a broadband continuous spectrum. The phase velocities of both types showed a similar mass dependency, approximately matching the ion sound velocity or electron diamagnetic drift velocity. Additionally, we found that the discrete spectrum has a peak interval frequency comparable to the ion cyclotron frequency, which is consistent with ion cyclotron ranges of fluctuations, including ion Bernstein waves.

DOI： 10.1063/5.0187997

Web of Science

Scopus

Language：English   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

<p>Turbulent transport by the ballooning mode in tokamak plasmas with edge pedestals is simulated using a reduced set of two-fluid equations. In the absence of the equilibrium poloidal flow, global heat transport by the secondary nonlinear evolution of the resistive ballooning mode turbulence is observed. By examining the effect of the edge shear flow, the global heat transport is suppressed to be almost half, if the edge shear flow is strong enough. A detailed analysis on the radial profile and the poloidal spectrum of the heat flux is newly performed. It is revealed that such confinement improvement is caused by the suppression of the formation of streamer structures that lead to the strong convective heat transport.</p>

DOI： 10.1585/pfr.19.1403016

Web of Science

Scopus

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Plasma Physics and Controlled Fusion  

The mutual interaction of drift wave-type modes and zonal flows causes the formation of higher-order nonlinear structures. This study focuses on the spatio-temporal behavior of these higher-order structures in a linear magnetized plasma. The structures include a solitary vortex, a long-lived circumnavigating motion localized both radially and azimuthally, and a short-lived packet of finer-scale fluctuations excited at the position of the solitary vortex. Observing the time evolution of the two-dimensional cross-sectional structures revealed that the packet of finer-scale fluctuations is trapped in the solitary vortex. The trapping times found are consistent with the theoretical evaluation.

DOI： 10.1088/1361-6587/acfbb3

Web of Science

Scopus

researchmap

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Spectral transition between continuous and discrete spectra has been observed in high-wavenumber turbulence excitation experiments. The transition appeared in neutral gas scanning, which shows that continuous spectra dominate at low gas pressures and discrete spectra dominate at high gas pressures. Both spectra have well smaller spatial scale than the ion effective Larmor radius. The discrete spectra have 6–11 peaks and maximum peak values at 4th or 5th peak. Correlation length analysis reveals that the continuous component is turbulent and the discrete component is coherent. The bicoherence analysis shows that the turbulent spectra have finite nonlinear coupling, whereas the discrete spectra have no corresponding coupling.

DOI： 10.1088/1361-6587/acfbf7

Web of Science

Scopus

researchmap

Other Link： https://iopscience.iop.org/article/10.1088/1361-6587/acfbf7/pdf

Language：English   Publishing type：Research paper (scientific journal)  

DOI： doi: 10.1063/5.0135918

Publisher：Physics of Plasmas  

Charged particle velocity-space diffusion in a prescribed one-dimensional turbulent electric field is investigated through numerical trajectories in phase-space and compared against quasi-linear theory (QL), including resonance broadening (RB). A Gaussian spectrum electric field of variable amplitude E is studied in conjunction with two plasma dispersion relations, namely, the Langmuir and ion-acoustic dispersion. A first parameter scan shows that RB effects become significant for a Kubo number K of a few percent. A Kubo number scan shows that diffusion increases as a power law of D K 3 E 3 / 2 for large Kubo numbers. Moreover, at large Kubo numbers, transport processes include significant diffusion measured at velocities much higher than the resonant region, where QL and RB predict negligible diffusion. For times much larger than the trapped particle flight time τb and the autocorrelation time τ0, the velocity distribution departs from a Gaussian. Nevertheless, measurements show that the variance increases linearly in time, with a Hurst parameter of H ∼ 0.5, where the diffusion scales as K 5 / 2 ∝ E 5 / 4 and K 3 / 2 ∝ E 3 / 4 for small and large Kubo number, respectively.

DOI： 10.1063/5.0135918

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

A procedure to calculate normalized electron temperature and electron density fluctuations using dual wavelength emission intensity tomography in a linear magnetized plasma is proposed. Expression of emission intensity is modeled as ϵk ∞ Tαke n2e where ϵk is emission intensity, Te is electron temperature, ne is electron density, k = 1 for ArI, and k = 2 for ArII. Using the model, normalized Te and ne fluctuations can be expressed as linear function of both the normalized emission intensity fluctuations. To calculate αk, we perform least squares method between real ϵk measured with a tomography system and artificial ϵk reconstructed using Te and ne measured with a Langmuir probe located downstream of the tomography system. The results show that α1 = 2.2 and α2 = 2.6, and normalized Te and ne fluctuations are preliminarily evaluated from emission intensity tomography data.

DOI： 10.7566/jpsj.92.033501

Web of Science

Scopus

CiNii Research

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

Enhancements of edge zonal flows, radial electric fields, and turbulence are observed in electron cyclotron resonance heating-heated plasmas (Zhao et al 2013 Nucl. Fusion 53 083011). In this paper, the effects of sawtooth heat pulses on flows and turbulence are presented. These experiments are performed using multiple Langmuir probe arrays in the edge plasmas of the HL-2A tokamak. The edge zonal flows, radial electric fields, and turbulence are all enhanced by sawteeth. Propagation of the zonal flow and turbulence intensities is also observed. The delay time of the maximal intensity of the electric fields, zonal flows, and turbulence with respect to the sawtooth crashes is estimated as similar to 1 ms and comparable to that of the sawtooth-triggered intermediate phases. Not only the zonal flows but also the radial electric fields lag behind the turbulence. Furthermore, the intensities of both the zonal flows and electric fields nearly linearly increase/decrease with the increase/decrease of the turbulence intensity. A double-source predator-prey model analysis suggests that a relatively strong turbulence source may contribute to the dominant zonal flow formation during sawtooth cycles.

DOI： 10.1088/2058-6272/ac7c60

Web of Science

Scopus

researchmap

Publisher：49th EPS Conference on Plasma Physics, EPS 2023  

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PORTFOLIO  

High-spatial resolution observation of high-wavenumber broadband turbulence is achieved by controlling the magnetic field to be relatively low and measuring with a azimuthally arranged multi-channel Langmuir array in a basic laboratory plasma. The observed turbulence consists of narrowband low-frequency fluctuations and broadband high-frequency turbulent fluctuations. The low-frequency fluctuations have a frequency of about 0.7 times the ion cyclotron frequency and a spatial scale of 1/10 of the ion inertial scale. In comparison, high-frequency fluctuations have a higher frequency than the ion cyclotron frequency and spatial scales of 1/10-1/40 of the ion inertial scale. Two-dimensional correlation analysis evaluates the spatial and temporal correlation lengths and reveals that the high-wavenumber broadband fluctuations have turbulent characteristics. The measurements give us further understanding of small scale turbulence in space and fusion plasmas.

DOI： 10.1038/s41598-022-23559-1

Web of Science

Scopus

PubMed

researchmap

Language：English   Publisher：AIP Publishing  

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

We present the evidence that drift waves can develop into nonlinear breathers. The theoretical analysis predicts that drift waves with secondary flow can excite the nonlinear breather through modulational instability. It is found that the simultaneous modulation of both amplitude and phase is a relevant feature of breather excitation. These features are used to elucidate the excitation of drift breather in a linear plasma experiment. The drift breathers are found to be excited frequently and intermittently. The transient increase in the transport flux is also demonstrated. We argue that there exists a critical condition on the wave amplitude for breather excitation.

DOI： doi: 10.1063/5.0122295

Repository Public URL： https://hdl.handle.net/2324/7173596

Publishing type：Research paper (scientific journal)   Publisher：Physics of Plasmas  

We present the evidence that drift waves can develop into nonlinear breathers. The theoretical analysis predicts that drift waves with secondary flow can excite the nonlinear breather through modulational instability. It is found that the simultaneous modulation of both amplitude and phase is a relevant feature of breather excitation. These features are used to elucidate the excitation of drift breather in a linear plasma experiment. The drift breathers are found to be excited frequently and intermittently. The transient increase in the transport flux is also demonstrated. We argue that there exists a critical condition on the wave amplitude for breather excitation.

DOI： 10.1063/5.0122295

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

<p>A solitary vortex organization process in drift-wave type fluctuations interacting with the zonal flow was identified experimentally in a linear magnetized plasma. An azimuthal probe array was used to evaluate temporal changes in the amplitude and phase in the density fluctuations. Excitation/damping of the solitary vortex is synchronized with zonal perturbation, and the waveform of drift-wave type fluctuation and its harmonics also changes synchronously. The solitary vortex is formed primarily through the phase modulation of the fundamental drift-wave type fluctuation and its harmonics.</p>

DOI： 10.1585/pfr.17.1301106

Web of Science

Scopus

CiNii Research

researchmap

Language：English   Publisher：The Japan Society of Plasma Science and Nuclear Fusion Research  

<p>In this study, in order to evaluate the SOL width of both density and temperature, we analyze Hasegawa-Wakatani model which includes the temperature fluctuations. Different instability regimes, i.e. drift waves and linearly unstable convective cells are studied. It is shown that convective cells are favorable in terms of the heat load reduction on the divertor. Implications on future devices, such as JT-60 SA, ITER, etc, are discussed.</p>

DOI： 10.1585/pfr.17.1403050

Web of Science

Scopus

CiNii Research

Publisher：Nuclear Fusion  

This conference report summarizes the contributions to, and discussions at the joint meeting of the 9th Asia Pacific-Transport Working Group (APTWG) & EU-US Transport Task Force (TTF) workshop held online, hosted by Kyushu University, Japan, during 6-9 July 2021. The topics of the meeting were organized under five main topics: (1) isotope effect on transport and physics on isotope mixture plasma, (2) turbulence spreading and coupling in core-edge-SOL, (3) interplay between magnetohydrodynamic topology/instability and turbulent transport, (4) interaction between energetic particle driven instability and transport, (5) model reduction and experiments for validation.

DOI： 10.1088/1741-4326/ac3f19

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The helicity of flow field is an important quantity for describing the topological feature of turbulent fluids and plasmas. In this work, we discuss how helicity is determined in turbulent plasmas, by considering the drift wave turbulence and the parallel velocity gradient driven turbulence as concrete examples. Helicity evolution for each turbulence is derived and compared against the simulation data. Links between the plasma helicity and the transport channels, such as particle transport and momentum transport, are demonstrated. Several applications including the excitation of the 3D flow patterns in fusion plasmas and dynamo action in astrophysical plasmas are discussed.

DOI： 10.1063/1.5121351

Language：English   Publishing type：Research paper (scientific journal)  

The dynamic features of triggering of type-III edge localized modes (ELMs) by macro-scale radially elongated flow (REF) in magnetically confined toroidal plasmas are presented. The REF, localized near the mid-plane and with a long radial correlation length at the low field side, was observed prior to the collapse of pedestal in series. It is demonstrated that the REF gets energy from and modulates ambient turbulence via nonlinear three wave interaction. The formation of REF leads to the onset of type-III ELMs, where the collapse of plasma energy occurs in the outer region ∼0.3 of the plasma column within a few tens of microseconds without global MHD instabilities. The path of the onset is identified and a clue to the trigger mechanism of violent events in high temperature plasmas is discussed.

DOI： 10.1088/1741-4326/ab742a

Language：English   Publishing type：Research paper (scientific journal)  

In this work, we discuss the physics behind the excitation of non-linear streamer flows in drift wave turbulence and how to selectively excite these flows. Streamer flows are modelled as a non-linear, radially elongated convective cell in drift wave turbulence. It is shown that density modulation is key for exciting streamer flows. We show that streamer flows have a finite frequency, albeit smaller than that of drift waves. Streamers propagate in the ion direction. These theoretical predictions are compared against experimental data, which shows reasonable agreement. Finally, the scrape-off layer width set by streamer flows is calculated, and a scaling law against macroscopic plasma parameters is obtained.

DOI： 10.1002/ctpp.201900141

Language：English   Publishing type：Research paper (scientific journal)  

A laser-induced fluorescence spectroscopy system was developed in a linear magnetized helicon plasma at Kyushu University. The thermal Doppler broadening on velocity distribution function follows the Maxwell distribution, and the averaged central ion temperature was evaluated to be ∼0.36 eV. The effect of Zeeman splitting was observed for a more accurate assessment of the measurement and is consistent with the calculation. The temperature ratio of electrons and ions, T_i/T_e, was evaluated to be ∼0.1. The result is valuable for evaluating the nonlinear processes of the plasma turbulence.

DOI： 10.1002/tee.22962

Language：English   Publishing type：Research paper (scientific journal)  

An analysis method is developed for imaging measurement systems, such as the tomography system or fast camera imaging, in order to extract the spatial structure properties of fluctuation. In this analysis method, rectangular functions and Fourier series are adopted for the basis functions of the radial and azimuthal coordinates, respectively. The examples of this analysis method show that this method is useful for quantifying the spatial structure of the 2D image such as the radial profile of the power and the rotation angle of each azimuthal mode. The method proposed in this article allows us to elucidate the features of the 2D spatial structure of phenomena in magnetized plasma.

DOI： 10.1063/1.5108717

Language：English   Publishing type：Research paper (scientific journal)  

We experimentally investigate the roles of drift wave type fluctuations interacting with zonal flow. The drift wave type fluctuations examined in this paper are characterized by nonlinear solitary wave, splash, and solitary eddy [Arakawa et al., Sci. Rep. 6, 33371 (2016)]. Compared to the nonlinear solitary wave, splash has a short lifetime, while solitary eddy has a long lifetime. Excitation/damping of the splash and the solitary eddy are synchronized with zonal perturbation. The roles of the splash and the solitary eddy in transport processes are also discussed. Solitary eddy contributes to momentum transport and accelerates zonal flow. The particle flux driven by the solitary eddy and the splash is in the inward and outward directions, respectively, with similar magnitudes.

DOI： 10.1063/1.5094577

Language：English   Publishing type：Research paper (scientific journal)  

We theoretically investigate turbulence in high-confinement mode (H-mode) plasmas with the pressure gradient and the mean flow. The toroidal flow, which is induced by the poloidal mean flow so as to satisfy the divergence free condition, exists in the H-mode, thus the effect of the toroidal return flow on instabilities is considered. The proposed model self-consistently includes not only the destabilization of the drift wave and the parallel flow shear instability, called the D'Angelo mode, but also the stabilization due to the poloidal flow shear. Depending on the strength of the flow shear or on the magnetic geometrical parameter, we obtain the stabilization of the drift wave and the destabilization of the D'Angelo mode. The competition between different instabilities through coupling of the poloidal flow with the toroidal return flow could be a key concept for understanding the turbulence in the H-mode. The characteristics of the instabilities are similar to the observations of the precursor of the type-III edge-localized mode.

DOI： 10.1088/1741-4326/ab1292

Language：English   Publishing type：Research paper (scientific journal)  

The streamer-driven particle flux is evaluated experimentally in a linear cylindrical plasma. The streamers, a radially elongated and azimuthally localized structure created in turbulent plasma, really induce ballistic transport, and directly connect the plasma core to the edge within one order faster time scale than that of turbulence. The occurrence of large transport deviates from a Gaussian distribution and is likely to obey a power law. The fundamental plasma experiment clearly shows the significant and essential contributions of streamers to cross-field transport and structural formation of turbulent plasmas.

DOI： 10.1063/1.5093218

Language：English   Publishing type：Research paper (scientific journal)  

We proposed a new method to evaluate particle flux in magnetized turbulent plasma. To extract fundamental fluctuation pattern, we used template method which is a kind of statistical conditional averaging technique. The method allows as not only to extract coherent patterns of density and potential fluctuations but also to evaluate time delay between them. We succeeded to calculate particle flux driven by fluctuation pattern and observed this pattern drives inward particle flux. Result obtained by the method is in good agreement with that obtained by a conventional method.

DOI： 10.1585/PFR.14.1402090

Language：English   Publishing type：Research paper (scientific journal)  

It is demonstrated that the zonal flow is controlled by the parallel flow in the cylindrical plasmas. A threedimensional turbulence simulation is performed, based on the reduced fluid model. The background parallel flow is applied by introducing the time independent parallel momentum source. Changing the magnitude of the momentum source, the behavior of the zonal flow is investigated. The drift wave turbulence is affected by the parallel flow, and it shows the spatial competition between turbulence modes. The spatial competition appears/disappears abruptly, depending on the intensity of the parallel momentum source. As a consequence of the transition between the turbulence state, the radial profile of the turbulence drastically changes, which leads to the change of the turbulence force to drive the zonal flow. In this way, the parallel flow indirectly affects the zonal flow through the deformation of the turbulence.

DOI： 10.1585/PFR.14.1401161

Language：English   Publishing type：Research paper (scientific journal)  

The role of density modulation in driving streamer flows in drift wave turbulence is discussed. In contrast to the conventional shearing mechanism, we emphasize the impact of frequency modulation by meso-scale density perturbation. This mechanism is more effective for streamers than for zonal flows. The Reynolds stress and nonlinear growth rate are calculated. The result indicates that the streamer growth is enhanced due to the density modulation. Implications on the selection of streamers and zonal flows are discussed as well.

DOI： 10.1063/1.5049726

Language：English   Publishing type：Research paper (other academic)  

Helical flow structure is ubiquitous in nature. In this short contribution, possible origins of these flow structures are presented. One is due to the parallel flow shear driven turbulence, where perpendicular zonal flows are nonlinearly excited. The other is conversion of perpendicular flows into parallel flows via phase space. Both processes highlight a fundamental process of helical flow generation in turbulent plasmas.

DOI： 10.1063/1.5048719

Language：English   Publishing type：Research paper (scientific journal)  

Streamers and their mediator have been known to exist in linear cylindrical plasmas [Yamada et al., Nat. Phys. 4, 721 (2008)]. Conditional averaging is applied to extract the nonlinear characteristics of a mediator, which has been simply treated as a linear wave. This paper reports that a mediator should have higher harmonic components generated by self-couplings, and the envelope of a streamer should be generated with not only fundamental but also higher harmonic components of the mediator. Moreover, both the mediator and the envelope of the streamer have common features with solitary waves, i.e., the height should increase inversely as the square of their localization width.

DOI： 10.1063/1.5027124

Language：English   Publishing type：Research paper (scientific journal)  

The spatio-temporal dynamics of turbulence with the interaction of geodesic acoustic modes (GAMs) are investigated, focusing on the phase-space structure of turbulence, where the phase-space consists of real-space and wavenumber-space. Based on the wave-kinetic framework, the coupling equation between the GAM and the turbulence is numerically solved. The turbulence trapped by the GAM velocity field is obtained. Due to the trapping effect, the turbulence intensity increases where the second derivative of the GAM velocity (curvature of the GAM) is negative. While, in the positive-curvature region, the turbulence is suppressed. Since the trapped turbulence propagates with the GAMs, this relationship is sustained spatially and temporally. The dynamics of the turbulence in the wavenumber spectrum are converted in the evolution of the frequency spectrum, and the simulation result is compared with the experimental observation in JFT-2M tokamak, where the similar patterns are obtained. The turbulence trapping effect is a key to understand the spatial structure of the turbulence in the presence of sheared flows.

DOI： 10.1063/1.5008541

Language：English   Publishing type：Research paper (scientific journal)  

As a result of the progresses in the study of plasma turbulence, the picture of 'multiple-scale turbulence' is widely accepted, and the 'nonlinear excitation, nonlocal interaction, probabilistic transition' views have been developed. Along the paths of these progresses, importance of new problem, i.e., the symmetry-breaking of turbulence structure (such as up-down asymmetry, excitation of streamer, etc.) is gradually recognized. In this topical review article, we revisit these issues, and illuminate the possibilities that the new progresses (which will be brought about by studying the symmetry-breaking of turbulence) are expected. Examining theoretical predictions and preceding experimental achievements, new advancements, which will be realized, are explained. The experimental study of symmetry-breaking of turbulence structure ultimately requires to measure fluctuations (at all scales) over the whole plasma cross-section simultaneously. In addition, new type of demands can be imposed in measuring of fluctuations over the whole plasma cross-section simultaneously. One of such demands is the accuracy of the measurement position. Problems in this aspect are also discussed. This concise review is used to identify what will be discovered and how it will be reached in future experiments, in the subject of the symmetry-breaking of turbulence structure.

DOI： 10.1585/PFR.13.1102113

Language：English   Publishing type：Research paper (scientific journal)  

Spatiotemporal structure of fluctuation with 11 kHz excited in a linear magnetized plasma was observed in details by applying pattern recognition method based on statistical averaging. Statistical behaviors of instantaneous period of the fluctuation and the temporal behavior of the radial profile of the fluctuation are clarified. Two-dimensional structure of the fluctuation is reconstructed and distortion of the wave-front of the fluctuation was inferred.

DOI： 10.1585/PFR.13.3401105

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (other academic)  

Language：English   Publishing type：Research paper (scientific journal)  

The three-dimensional structures of the streamer and its carrier waves and mediator were observed in a linear plasma device for the first time. Not only the cross-sectional structure but also the axial structure was observed. While carrier drift waves, which form the streamer structure by nonlinear interaction, had an axial mode number of 1, the streamer and mediator had an axial mode number of 0. The relationship of these axial mode numbers is well explained by the matching condition of the nonlinear interaction between the carrier waves and the mediator.

DOI： 10.7566/JPSJ.87.034501

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel mechanism of enhancement of turbulence by energetic-particle-driven geodesic acoustic modes (EGAMs). The dynamics of drift-wave-type turbulence in the phase space is investigated by wave-kinetic equation. Spatially inhomogeneous turbulence in the presence of a transport barrier is considered. We discovered that trapping of turbulence clumps by the EGAMs is the key parameter that determines either suppress or enhance turbulence. In regions where turbulence is unstable, EGAM suppresses the turbulence. In contrast, in the stable region, EGAM traps clumps of turbulence and carries them across the transport barrier, so that the turbulence can be enhanced. The turbulence trapped by EGAMs can propagate independent of the gradients of density and temperature, which leads to non-Fickian transport. Hence, there appear a new global characteristic velocity, the phase velocity of GAMs, for turbulence dynamics, in addition to the local group velocity and that of the turbulence spreading. With these effect, EGAMs can deteriorate transport barriers and affect turbulence substantially. This manuscript provides a basis to consider whether a coherent wave breaks or strengthen transport barriers.

DOI： 10.1038/s41598-017-17011-y

Language：English   Publishing type：Research paper (scientific journal)  

The role of parallel shear flow in the pattern selection problem in drift wave turbulence is discussed. Patterns of interest here are E × B convective cells, which include poloidally symmetric zonal flows and radially elongated streamers. The competition between zonal flow formation and streamer formation is analyzed in the context of modulational instability analysis, with the parallel flow shear as a parameter. For drift wave turbulence with k∥ρs ≲ O(1) and without parallel flow coupling, zonal flows are preferred structures. While increasing the magnitude of parallel flow shear, streamer growth overcomes zonal flow growth. This is because the self-focusing effect of the modulational instability becomes more effective for streamers through density and parallel velocity modulation. As a consequence, the bursty release of free energy may result as the parallel flow shear increases.

DOI： 10.1063/1.5001857

Language：English   Publishing type：Research paper (scientific journal)  

The topological bifurcation of the flow in non-equilibrium magnetized plasmas is demonstrated by a turbulence simulation. A system with two generic sources of turbulence, the gradients of density and parallel flow, is considered. Topological index of the flow is introduced, in order to indicate the chirality of flow pattern. We here report that the turbulence-driven flow forms the structure of co-axial helixes with opposite chirality. By changing the source of plasma particles, which modifies the density gradient, the transition between three turbulent states is obtained. In addition to the two turbulent states, which are dominated by the drift wave and the D'Angelo mode, respectively, the new state is found. In this third state, fluctuations are driven by both of the free energy sources simultaneously, and compete with the others. The result illustrates the generic feature of turbulence flow generation in non-equilibrium magnetized plasmas.

DOI： 10.1063/1.5000343

Language：English   Publishing type：Research paper (scientific journal)  

The temporal-spatial structures of plasma flows and turbulence around tearing mode islands are presented. The experiments were performed using Langmuir probe arrays in the edge plasmas of J-TEXT tokamak. The correlation analyses clearly show that the flows have similar structures of m/n = 3/1 as the magnetic island does (m and n are the poloidal and toroidal mode numbers, respectively). The sign of the potential fluctuations for the flows inverses and the powers significantly reduce at q = 3 surface. Approaching to the last closed flux surface for the magnetic islands, the radially elongated flow structure forms. The flows are concentrated near separatrix and show quadrupole structures. The turbulence is concentrated near X-point and partly trapped inside the magnetic islands.

DOI： 10.1088/1741-4326/aa8341

Language：English   Publishing type：Research paper (scientific journal)  

This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradientflux relation. The key finding is that hystereses were observed simultaneously in both the the gradientflux and gradientfluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation δTm in heating modulation experiments. The hysteresis introduces the term δTm, which depends on the harmonic number m in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for the heating heats turbulence is that the external source S in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on confinement. Finally, the impacts of transport hysteresis on the control system are assessed. Control systems must be designed so as to protect the system from sudden plasma loss.

DOI： 10.1088/1741-4326/aa796a

Language：English   Publishing type：Research paper (scientific journal)  

Changes in the core intrinsic toroidal rotation velocity following L- to H- and L- to I-mode transitions have been investigated in Alcator C-Mod tokamak plasmas. The magnitude of the co-current rotation increments is found to increase with the pedestal temperature gradient and q95, and to decrease with toroidal magnetic field. These results are captured quantitatively by a model of fluctuation entropy balance which gives the Mach number M_i ≃= -rfpag∗/2L_s/L_T∇Tq95/BT in an ITG turbulence dominant regime. The agreement between experiment and theory gives confidence for extrapolation to future devices in similar operational regimes. Core thermal Mach numbers of ∼0.07 and ∼0.2 are expected for ITER and ARC, respectively.

DOI： 10.1088/1741-4326/aa7b44

Language：English   Publishing type：Research paper (scientific journal)  

New mesoscale electric fluctuations (MSEFs) are identified in the edge plasmas of the HL-2A tokamak using multiple Langmuir probe arrays. The MSEFs, resulting from the synchronization and having components of dominant geodesic acoustic mode (GAM) and m/n = 6/2 potential fluctuations, are found at the same frequency as that of the magnetic fluctuations of m/n = 6/2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m/n = 6/2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. The nonlinear coupling analyses show that the MSEFs couple to turbulence and low frequency zonal flows (LFZFs). This suggests that the MSEFs may contribute to the LFZF formation, reduction of turbulence level, and thus confinement regime transitions. The analysis of the envelope modulation demonstrates that both the MSEFs and the LFZFs modulate the turbulence while the MSEFs are modulated by the LFZFs.

DOI： 10.1088/1741-4326/aa6f35

Language：English   Publishing type：Research paper (scientific journal)  

The abrupt and strong excitation of the geodesic acoustic mode (GAM) has been found in the large helical device (LHD), when the frequency of a chirping energetic particle-driven GAM (EGAM) approaches twice that of the GAM frequency. The temporal evolution of the phase relation between the abrupt GAM and the chirping EGAM is common in all events. The result indicates a coupling between the GAM and the EGAM. In addition, the nonlinear evolution of the growth rate of the GAM is observed, and there is a threshold in the amplitude of the GAM for the appearance of nonlinear behavior. A threshold in the amplitude of the EGAM for the abrupt excitation of the GAM is also observed. According to one theory (Lesur et al 2016 Phys. Rev. Lett. 116 015003, Itoh et al 2016 Plasma Phys. Rep. 42 418) the observed abrupt phenomenon can be interpreted as the excitation of the subcritical instability of the GAM. The excitation of a subcritical instability requires a trigger and a seed with sufficient amplitude. The observed threshold in the amplitude of the GAM seems to correspond with the threshold in the seed, and the threshold in the amplitude of the EGAM seems to correspond with the threshold in the magnitude of the trigger. Thus, the observed threshold supports the interpretation that the abrupt phenomenon is the excitation of a subcritical instability of the GAM.

DOI： 10.1088/1741-4326/aa665a

Language：English   Publishing type：Research paper (scientific journal)  

The hydrogen isotope effect on confinement is discussed by investigating the coupling between confinement, wall material and scrape-off-layer (SoL) turbulence. An emphasis is placed upon the dependence of the neutral density on the hydrogen mass number. The momentum loss via CX process in the barrier is studied, and its influence on the radial electric field in the barrier (so as to modify the suppression of transport) is discussed. The penetration of slow neutrals and the reflection of fast neutrals on the wall are considered. Combining these processes, the influence of hydrogen mass number on the atomic, molecular, material and plasma interactions is investigated. The penetration of strong fluctuations in the SoL plasma into the confined plasma via the fuelling of neutral particles (i.e. fuelling fuels turbulence) is also discussed. The hydrogen isotope effect on this source of edge turbulence, which can affect the core-confinement, is discussed.

DOI： 10.1088/1741-4326/aa65eb

Language：English   Publishing type：Research paper (scientific journal)  

In fusion plasmas, several mechanisms such as heating, wave-particle interaction etc can drive deviations of distribution function from Maxwelian to form phase space structures. This article discusses the impact of phase space structures in drift wave turbulence on dynamics and transport modeling. The two cases of (i) coherent holes and (ii) incoherent granulations (clusters of correlated resonant particles with finite life time) are treated. Their dynamical impact on driving subcritical instability is analyzed by explicitly calculating the nonlinear growth rate. The role of zonal flows is also addressed. It is explained how phase space structures can be related to transient events and non-diffusive transport, issues in current confinement research.

DOI： 10.1088/1741-4326/57/7/072006

Language：English   Publishing type：Research paper (scientific journal)  

A calculation which describes the spin-up of toroidal plasmas by the radial propagation of turbulence fronts with broken parallel symmetry is presented. The associated flux of parallel momentum is calculated by using a two-scale direct-interaction approximation in the weak turbulence limit. We show that fluctuation momentum spreads faster than mean flow momentum. Specifically, the turbulent flux of wave momentum is stronger than the momentum pinch. The scattering of fluctuation momentum can induce edge-core coupling of toroidal flows, as observed in experiments.

DOI： 10.1103/PhysRevE.95.031203

Language：English   Publishing type：Research paper (scientific journal)  

Toroidal momentum channeling by fast ion-driven geodesic acoustic mode (EGAM) is proposed based on a quasi-linear analysis. We focus on a branch due to the magnetic drift resonance. Without the magnetic drift resonance, the eigenfunction of the EGAM has up-down anti-symmetric property in the poloidal direction, and the toroidal momentum flux by the EGAM is zero. If the magnetic drift resonance is considered, the up-down anti-symmetry in the poloidal eigenfunction is violated, and, as a result, the toroidal momentum flux becomes finite. Comparing its magnitude to the other processes such as external momentum input, and the turbulent residual stress, the momentum flux induced by the EGAM is found to be significant in the total momentum balance. This suggests that EGAMs can be used as a control knob for the toroidal rotation.

DOI： 10.1088/1741-4326/aa4eb4

Language：English   Publishing type：Research paper (scientific journal)  

Generation of zonal flow in parallel flow shear driven turbulence is discussed. Nonlinear dynamics is formulated by calculating energy transfer in the wave number space. It is shown that zonal flows can be generated (gain energy) from the primary mode which is driven by parallel flow shear. As a result, helical flow pattern can develop in turbulent plasmas. Our results imply that zonal flow can be generated in 3D parallel flow shear driven turbulence, which indicates that zonal flows are ubiquitous in turbulent plasmas, either 2D or 3D. Implications for turbulent momentum transport in laboratory and astrophysical plasmas are discussed.

DOI： 10.1063/1.4978485

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Changing the experimental conditions such as the neutral pressure and the magnetic field strength provides a drastic change in the turbulence states in linear magnetized helicon plasmas. In order to define the turbulence states and their occurrence region a throughout parameter scan in the two-dimensional parameter space was performed. The classification of the turbulence states is carried out phenomenologically based on the turbulence spectrum and the waveform.

DOI： 10.1585/pfr.12.1401019

Language：English   Publishing type：Research paper (scientific journal)  

Bispectrum and bicoherence analysis is a powerful method to analyze nonlinear interaction of turbulent plasmas. In this review, we explain the difference of the bispectrum and bicoherence analysis and possible research that can be pursued with these methods. Basic concept is explained by using several examples from previous successes brought by bicoherence and bispectrum analysis, such as drift wave-zonal flow interaction. Open questions are discussed that can be challenged by these methods. Problems such as spatial transport of fluctuation energy (i.e. turbulence spreading), momentum transport by the triplet correlation, and so on, are treated. Bispectrum and bicoherence analysis can be utilized to expand the forefront of plasma turbulence research.

DOI： 10.1585/pfr.12.1101003

Language：English   Publishing type：Research paper (scientific journal)  

A new type of nonlinear coupling among multi-time scale of fluctuations is observed on the linear plasma device, PANTA. The low frequency drift waves (DWs), a few kHz and a high frequency fluctuation (the HF fluctuation) (~ 30 kHz) are simultaneously observed. These fluctuations nonlinearly couple with each other confirmed by bi-coherence analysis. The characteristics of HF fluctuation are also discussed.

DOI： 10.1585/pfr.12.1201034

Language：English   Publishing type：Research paper (scientific journal)  

Multiple free energy sources for instabilities coexist in magnetized plasmas with density gradient and velocity shear. Linear stabilities are investigated, and the mutual relation between resistive drift wave, D'Angelo mode and flute mode is systematically clarified. By evaluating the linear growth rates, dominant instability is categorized in a parameter space. The parallel wavenumber spectrum could be used as a guideline for the identification of the instabilities.

DOI： 10.1585/pfr.12.1401042

Language：English   Publishing type：Research paper (scientific journal)  

Experimental plasma discharges in linear PANTA device are studied by Mach probe measurements, providing floating potential, ion saturation current, and parallel flow velocity time evolution, at different radii of the device. Spectral analysis indicates that drift waves and D'Angelo modes exist simultaneously in the plasma. A discrimination study shows they are located at different positions in radius and frequency.

DOI： 10.1585/pfr.12.1201008

Language：English   Publishing type：Research paper (scientific journal)  

Trapped ion resonance-driven turbulence is investigated in the presence of electron dissipation in a simplified tokamak geometry. A reduced gyrokinetic bounce-averaged model for trapped ions is adopted. Electron dissipation is modeled by a simple phase-shift δ between density and electric potential perturbations. The linear eigenfunction features a peak at the resonant energy, which becomes stronger with increasing electron dissipation. Accurately resolving this narrow peak in numerical simulation of the initial-value problem yields a stringent lower bound on the number of grid points in the energy space. Further, the radial particle flux is investigated in the presence of electron dissipation, including kinetic effects. When the density gradient is higher than the temperature gradient, and the phase-shift is finite but moderate (δ<0.02), the particle flux peaks at an order-of-magnitude above the gyro-Bohm estimate. Slight particle pinch is observed for δ<0.003.

DOI： 10.1063/1.4974269

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In fusion plasmas, several mechanisms such as heating, wave-particle interaction etc can drive deviations of distribution function from Maxwelian to form phase space structures. This article discusses the impact of phase space structures in drift wave turbulence on dynamics and transport modeling. The two cases of (i) coherent holes and (ii) incoherent granulations (clusters of correlated resonant particles with finite life time) are treated. Their dynamical impact on driving subcritical instability is analyzed by explicitly calculating the nonlinear growth rate. The role of zonal flows is also addressed. It is explained how phase space structures can be related to transient events and non-diffusive transport, issues in current confinement research.

Language：English   Publishing type：Research paper (scientific journal)  

Eigenmode analysis of geodesic acoustic modes (GAMs) driven by fast ions is performed, based on a set of gyrokinetic equations. Resonance to the magnetic drift of the fast ions can destabilize GAMs. A new branch is found in the family of GAMs, whose frequency is close to the magnetic drift frequency of the fast ions. The poloidal eigenfunction of this branch has bump structures in the poloidal direction where the resonance of the magnetic drift with the mode is strong. The ion heating rate by the GAMs is evaluated in the framework of quasi-linear theory. The heating is localized poloidally around the resonance locations. Owing to the bumps in the eigenfunction, the magnitude of the heating is much larger than that estimated without the magnetic drift resonance.

DOI： 10.1063/1.4963397

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we show the direct observation of the parallel flow structure and the parallel Reynolds stress in a linear magnetized plasma, in which a cross-ferroic turbulence system is formed [Inagaki et al., Sci. Rep. 6, 22189 (2016)]. It is shown that the parallel Reynolds stress induced by the density gradient driven drift wave is the source of the parallel flow structure. Moreover, the generated parallel flow shear by the parallel Reynolds stress is found to drive the parallel flow shear driven instability D'Angelo mode, which coexists with the original drift wave. The excited D'Angelo mode induces the inward particle flux, which seems to help in maintaining the peaked density profile.

DOI： 10.1063/1.4965915

Language：English   Publishing type：Research paper (scientific journal)  

Here we report changes in the turbulence spectrum and turbulence-driven particle flux during end-plate biasing experiments in a linear plasma. Outward radial flux driven by drift waves is decreased as the amplitude of the drift waves is reduced. During biasing, the cross-phase between potential and density fluctuations of mediator, which plays a key role in nonlinear interactions of turbulence, changed from negative to positive. Then the radial flux is induced reversal from inward to outward.

DOI： 10.7566/JPSJ.85.093501

Language：English   Publishing type：Research paper (scientific journal)  

The synchronization of geodesic acoustic modes (GAMs) and magnetic fluctuations is identified in the edge plasmas of the HL-2A tokamak. Mesoscale electric fluctuations (MSEFs) having components of a dominant GAM, and m/n=6/2 potential fluctuations are found at the same frequency as that of the magnetic fluctuations of m/n=6/2 (m and n are poloidal and toroidal mode numbers, respectively). The temporal evolutions of the MSEFs and the magnetic fluctuations clearly show the frequency entrainment and the phase lock between the GAM and the m/n=6/2 magnetic fluctuations. The results indicate that GAMs and magnetic fluctuations can transfer energy through nonlinear synchronization. Such nonlinear synchronization may also contribute to low-frequency zonal flow formation, reduction of turbulence level, and thus confinement regime transitions.

DOI： 10.1103/PhysRevLett.117.145002

Language：English   Publishing type：Research paper (scientific journal)  

In this article, we discuss a method to identify whether the observed perturbation in toroidal plasmas is a quasi-electrostatic perturbation or not. A criterion is derived based on the observed data of plasma deformation and external magnetic perturbations. This result can be applied to the study of properties of quasi-modes, which have been observed in toroidal plasmas.

DOI： 10.7566/JPSJ.85.094504

Language：English   Publishing type：Research paper (scientific journal)  

Turbulence and its structure formation are universal in neutral fluids and in plasmas. Turbulence annihilates global structures but can organize flows and eddies. The mutual-interactions between flow and the eddy give basic insights into the understanding of non-equilibrium and nonlinear interaction by turbulence. In fusion plasma, clarifying structure formation by Drift-wave turbulence, driven by density gradients in magnetized plasma, is an important issue. Here, a new mutual-interaction among eddy, drift wave and flow in magnetized plasma is discovered. A two-dimensional solitary eddy, which is a perturbation with circumnavigating motion localized radially and azimuthally, is transiently organized in a drift wave-zonal flow (azimuthally symmetric band-like shear flows) system. The excitation of the eddy is synchronized with zonal perturbation. The organization of the eddy has substantial impact on the acceleration of zonal flow.

DOI： 10.1038/srep33371

Language：English   Publishing type：Research paper (scientific journal)  

Theory of parallel shear flow driven instability (PSFI) and its impact on turbulence dynamics and transport are presented. The mode is linearly unstable when the parallel flow shear exceeds a critical value. The quasilinear particle flux contains both outward and inward components. Nonlinear dynamics is formulated in terms of hydrodynamic helicity balance. The result implies that once excited, PSFI with helicity may spread from the excited region to stable regions. Implication for turbulence in scrape off layer plasmas is discussed. (

DOI： 10.1002/ctpp.201610047

Language：English   Publishing type：Research paper (scientific journal)  

An analytic model is developed for understanding the abrupt onset of geodesic acoustic mode (GAM) in the presence of chirping energetic-particle-driven GAM (EGAM). This abrupt excitation phenomenon has been observed on LHD plasma. Threshold conditions for the onset of abrupt growth of GAM are derived, and the period doubling phenomenon is explained. The phase relation between the mother mode (EGAM) and the daughter mode (GAM) is also discussed. This result contributes to the understanding of “trigger problems” of laboratory and nature plasmas.

DOI： 10.1134/S1063780X16050056

Language：English   Publishing type：Research paper (scientific journal)  

In collisionless plasma, it is known that linearly stable modes can be destabilized (subcritically) by the presence of structures in phase-space. The growth of such structures is a nonlinear, kinetic mechanism, which provides a channel for free-energy extraction, different from conventional inverse Landau damping. However, such nonlinear growth requires the presence of a seed structure with a relatively large threshold in amplitude. We demonstrate that, in the presence of another, linearly unstable (supercritical) mode, wave-wave coupling can provide a seed, which can lead to subcritical instability by either one of two mechanisms. Both mechanisms hinge on a collaboration between fluid nonlinearity and kinetic nonlinearity. If collisional velocity diffusion is low enough, the seed provided by the supercritical mode overcomes the threshold for nonlinear growth of phase-space structure. Then, the supercritical mode triggers the conventional subcritical instability. If collisional velocity diffusion is too large, the seed is significantly below the threshold, but can still grow by a sustained collaboration between fluid and kinetic nonlinearities. Both of these subcritical instabilities can be triggered, even when the frequency of the supercritical mode is rapidly sweeping. These results were obtained by modeling the subcritical mode kinetically, and the impact of the supercritical mode by simple wave-wave coupling equations. This model is applied to bursty onset of geodesic acoustic modes in an LHD experiment. The model recovers several key features such as relative amplitude, timescales, and phase relations. It suggests that the strongest bursts are subcritical instabilities, with sustained collaboration between fluid and kinetic nonlinearities.

DOI： 10.1088/0029-5515/56/5/056009

Language：English   Publishing type：Research paper (scientific journal)  

The variety of scalar and vector fields in laboratory and nature plasmas is formed by plasma turbulence. Drift-wave fluctuations, driven by density gradients in magnetized plasmas, are known to relax the density gradient while they can generate flows. On the other hand, the sheared flow in the direction of magnetic fields causes Kelvin-Helmholtz type instabilities, which mix particle and momentum. These different types of fluctuations coexist in laboratory and nature, so that the multiple mechanisms for structural formation exist in extremely non-equilibrium plasmas. Here we report the discovery of a new order in plasma turbulence, in which chained structure formation is realized by cross-interaction between inhomogeneities of scalar and vector fields. The concept of cross-ferroic turbulence is developed, and the causal relation in the multiple mechanisms behind structural formation is identified, by measuring the relaxation rate and dissipation power caused by the complex turbulence-driven flux.

DOI： 10.1038/srep22189

Language：English   Publishing type：Research paper (scientific journal)  

The influence of relative displacement of Mach probe (which is placed near the top of magnetic surface) on the interference of signals is discussed. An error can arise in measured value of poloidal electric field. The Mach number perturbation at the GAM frequency has an interference from the density perturbation. The interference from the density perturbation can propagate to all of Mach number measurement. By observing the signals associated with GAM oscillations, the error in setting the probe arrays can be detected. This result can be applied to correct the positioning of probes.

DOI： 10.1585/pfr.11.1402002

Language：English   Publishing type：Research paper (scientific journal)  

We improved the signal-to-noise ratio of a Reynolds stress (RS) probe in order to measure the Reynolds stress more accurately. By introducing a shield pipe in the probe, the power spectral density of the noise was suppressed to approximately one tenth in an electric biasing experiment. It was also confirmed that the leak current in the RS probe, which had been used in previous experiments, was small enough for the study of drift waves in our linear device.

DOI： 10.1585/pfr.11.1201091

Language：English   Publishing type：Research paper (scientific journal)  

The flux of parallel momentum by parallel shear flow driven instability is calculated with the self-consistent mode dispersion. The result indicates that the diffusive component has two characteristic terms: v_D1 ~ v˜_x²/γ(0) and v_D2 ~ v˜_x²/(k_||² D_||) where v˜_x is the fluctuation radial velocity, γ(0) is the growth rate of the mode, k_|| is the parallel wave number, and D_|| is the electron diffusivity along the magnetic field. vD1 results when the parallel flow shear is above the threshold, while v_D2 is important around the marginal state. Since typically v_D1 ≫ v_D2 ~ D_n, where Dn is the particle diffusivity, the Prandtl number (≡ v/D_n) becomes large when parallel flow shear driven instability occurs. This feature may explain the experimental observation on the difference between profiles of density and toroidal flow in edge and SOL plasmas.

DOI： 10.1585/pfr.11.1203018

Language：English   Publishing type：Research paper (scientific journal)  

Fluctuation component in the turbulence regime is found to be azimuthally localized at a phase of the global coherent modes in a linear magnetized plasma PANTA. Spatial distribution of squared bicoherence is given in the azimuthal cross section as an indicator of nonlinear energy transfer function from the global coherent mode to the turbulence. Squared bicoherence is strong at a phase where the turbulence amplitude is large. As a result of the turbulence localization, time evolution of radial particle flux becomes bursty. Statistical features such as skewness and kurtosis are strongly modified by the localized turbulence component, although contribution to mean particle flux profile is small.

DOI： 10.1063/1.4934537

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We present a theory of turbulence elasticity, which follows from delayed response of drift waves (DWs) to zonal flow (ZF) shears. It is shown that when |V′_ZF|/Δω_k1, with |V′_ZF| the ZF shearing rate and Δω_k the local turbulence decorrelation rate, the ZF evolution equation is converted from a diffusion equation to a telegraph equation. This insight provides a natural framework for understanding temporally periodic ZF structures, e.g., propagation of the ZF/turbulence intensity fronts. Furthermore, by incorporating the elastic property of the DW-ZF turbulence, we propose a unified paradigm of low-confinement-mode to intermediate-confinement-mode to high-confinement-mode (L→I→H) transitions. In particular, we predict the onset and termination conditions of the limit cycle oscillations, i.e. the I-mode. The transition from an unstable L-mode to I-mode is predicted to occur when Δω_k<|V′_ZF|<V′_cr, where V′_cr is a critical flow shearing rate and is derived explicitly. If |V′_E×B|>V′_cr (V_EB is mean E×B shear flow driven by edge radial electrostatic field), the I-mode will terminate and spiral into the H-mode.

DOI： 10.1088/0029-5515/55/4/043022

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Turbulence in hot magnetized plasmas is shown to generate permeable localized transport barriers that globally organize into the so-called "ExB staircase" [G. Dif-Pradalier et al., Phys. Rev. E, 82, 025401(R) (2010)]. Its domain of existence and dependence with key plasma parameters is discussed theoretically. Based on these predictions, staircases are observed experimentally in the Tore Supra tokamak by means of high-resolution fast-sweeping X-mode reflectometry. This observation strongly emphasizes the critical role of mesoscale self-organization in plasma turbulence and may have far-reaching consequences for turbulent transport models and their validation.

DOI： 10.1103/PhysRevLett.114.085004

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, recent progress on experimental analysis and theoretical models for non-local transport (non-Fickian fluxes in real space) is reviewed. The non-locality in the heat and momentum transport observed in the plasma, the departures from linear flux-gradient proportionality, and externally triggered non-local transport phenomena are described in both L-mode and improved-mode plasmas. Ongoing evaluation of 'fast front' and 'intrinsically non-local' models, and their success in comparisons with experimental data, are discussed

DOI： 10.1088/0029-5515/55/1/013022

Language：English   Publishing type：Research paper (scientific journal)  

We have tested the telegraph equation for transport dynamics in magnetized plasma by comparing its resultswith experimental observations in the Large Helical Device [S. Inagaki et al., Nucl. Fusion 53, 113006 (2013)]. The telegraph equation includes a finite relaxation time for turbulence intensity in response to the changes in global plasma parameters. This model was applied to nondiffusive radial heat pulse propagation under the periodic modulation of the heating power. The model showed some success in reproducing the amplitudes of higher harmonics. However, the phase relation between the temperature gradient and heat flux was opposite to that in experimental observations.

DOI： 10.1585/pfr.10.1203002

Language：English   Publishing type：Research paper (scientific journal)  

To understand turbulent transport in magnetized plasmas, an end-plate biasing experiment was performed in a linear magnetized plasma device, PANTA. Here we report the change of bi-coherence among fluctuations during biasing. During biasing, coupling with drift waves is decrease, and that with the mediator is increase.

DOI： 10.1585/pfr.10.3401043

Language：English   Publishing type：Research paper (scientific journal)  

A theory to describe coupled dynamics of drift waves and D'Angelo modes is presented. The coupled dynamics is formulated by calculating fluctuation energy evolution. When drift waves dominate, turbulence production is due to release of free energy in density profile. Drift waves in turn exert Reynolds stress to drive secondary axial flows. When parallel flow shear is strong, D'Angelo modes dominate. Turbulent production occurs from release of free energy in parallel flow shear. D'Angelo modes can generate a secondary structure in density profile and can peak density profile. It is shown that when D'Angelo modes are unstable, they necessarily contribute to an inward particle flux, that compete against an outward, down-gradient flux. Net inward, upgradient particle flux can result for strong flow shear, which can lead to density peaking in plasmas. Application to laboratory and astrophysical plasmas is discussed.

DOI： 10.1585/pfr.10.3401024

Language：English   Publishing type：Research paper (scientific journal)  

This conference report summarizes the contributions to, and discussions at, the 4th Asia-Pacific Transport Working Group Meeting held at Kyushu University, Japan, during 10-13 June 2014. The topics of the meeting were organized under five main headings: turbulence suppression and transport barrier formation, effect of magnetic topology on MHD activity and transport, non-diffusive contribution of momentum and particle transport, non-local transport and turbulence spreading and coupling, energetic particles and instability. The Young Researchers' Forum which was held in this meeting is also described in this report.

DOI： 10.1088/0029-5515/55/1/017001

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

In the presence of wave dissipation, phase-space structures spontaneously emerge in nonlinear Vlasov dynamics. These structures include not only well-known self-trapped vortices (holes) but also elongated filaments, resembling jets, as reported in this work. These jets are formed by straining due to interacting holes. Jets are highly anisotropic, and connect low and high velocity regions over a range larger than the electron thermal velocity. Jets survive long enough for particles to scatter between low and high phase-space density regions. Jets are found to contribute significantly to electron redistribution, velocity-space transport, and anomalous resistivity.

DOI： 10.1063/1.4902525

Language：English   Publishing type：Research paper (scientific journal)  

Meso-scale streamer has a radially elongated structure and is believed to enhance the radial transport. In order to study the control of the streamer, we demonstrated an end plate biasing to the streamer state in the PANTA linear plasma. During the end plate biasing, the electron density profile became more peaked, fluctuation was suppressed, the streamer structure was deconstructed, and the waveform became a periodic solitary state. The radial electric field only induced at around the end plate was found to play an important role for the streamer suppression.

DOI： 10.1088/0029-5515/54/11/114010

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A theory to describe basic characterization of ion temperature gradient driven turbulence with strong trapped ion resonance is presented. The role of trapped ion granulations, clusters of trapped ions correlated by precession resonance, is the focus. Microscopically, the presence of trapped ion granulations leads to a sharp (logarithmic) divergence of two point phase space density correlation at small scales. Macroscopically, trapped ion granulations excite potential fluctuations that do not satisfy dispersion relation and so broaden frequency spectrum. The line width from emission due only to trapped ion granulations is calculated. The result shows that the line width depends on ion free energy and electron dissipation, which implies that non-adiabatic electrons are essential to recover non-trivial dynamics of trapped ion granulations. Relevant testable predictions are summarized.

DOI： 10.1063/1.4897179

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We present a new, unified model of transport barrier formation in " elastic" drift wave-zonal flow (DW-ZF) turbulence. A new physical quantity - the delay time (i.e., the mixing time for the DW turbulence) - is demonstrated to parameterize each stage of the transport barrier formation. Quantitative predictions for the onset of limit-cycle-oscillation (LCO) among DW and ZF intensities (also denoted as I-mode) and I-mode to high-confinement mode (H-mode) transition are also given. The LCO occurs when the ZF shearing (|〈v〉ZF′|) enters the regime Δωk<|〈V〉 ZF′|<τcr-1, where Δω_k is the local turbulence decorrelation rate and τ_cr is the threshold delay time. In the basic predator-prey feedback system, τ_cr is also derived. The I-H transition occurs when |〈V〉E×B′|>τ cr-1, where the mean E×B shear flow driven by ion pressure "locks" the DW-ZF system to the H-mode by reducing the delay time below the threshold value.

DOI： 10.1063/1.4894695

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The nonlinear stability of current-driven ion-acoustic waves in collisionless electron-ion plasmas is analyzed. Seminal simulations from the 1980s are revisited. Accurate numerical treatment shows that subcritical instabilities do not grow from an ensemble of waves, except very close to marginal stability and for large initial amplitudes. Further from marginal stability, one isolated phase-space structure can drive subcritical instabilities by stirring the phase-space in its wake. Phase-space turbulence, which includes many structures, is much more efficient than an ensemble of waves or an isolated hole for driving subcritically particle redistribution, turbulent heating and anomalous resistivity. Phase-space jets are observed in subcritical simulations.

DOI： 10.1088/0741-3335/56/7/075005

Language：English   Publishing type：Research paper (scientific journal)  

A novel theory to describe the formation of E×B flow patterns by radially propagating heat flux waves is presented. A model for heat avalanche dynamics is extended to include a finite delay time between the instantaneous heat flux and the mean flux, based on an analogy between heat avalanche dynamics and traffic flow dynamics. The response time introduced here is an analogue of the drivers' response time in traffic dynamics. The microscopic foundation for the time delay is the time for mixing of the phase space density. The inclusion of the finite response time changes the model equation for avalanche dynamics from Burgers equation to a nonlinear telegraph equation. Based on the telegraph equation, the formation of heat flux jams is predicted. The growth rate and typical interval of jams are calculated. The connection of the jam interval to the typical step size of the E×B staircase is discussed.

DOI： 10.1063/1.4872018

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We present a theory of turbulent elasticity, a property of drift-wave-zonal-flow (DW-ZF) turbulence, which follows from the time delay in the response of DWs to ZF shears. An emergent dimensionless parameter |〈v〉|/Δωk is found to be a measure of the degree of Fickian flux-gradient relation breaking, where |〈v〉| is the ZF shearing rate and Δωk is the turbulence decorrelation rate. For |〈v〉|/Δωk>1, we show that the ZF evolution equation is converted from a diffusion equation, usually assumed, to a telegraph equation, i.e., the turbulent momentum transport changes from a diffusive process to wavelike propagation. This scenario corresponds to a state very close to the marginal instability of the DW-ZF system, e.g., the Dimits shift regime. The frequency of the ZF wave is ΩZF=±γd1/2γmodu1/2, where γd is the ZF friction coefficient and γmodu is the net ZF growth rate for the case of the Fickian flux-gradient relation. This insight provides a natural framework for understanding temporally periodic ZF structures in the Dimits shift regime and in the transition from low confined mode to high confined mode in confined plasmas.

DOI： 10.1103/PhysRevE.89.041101

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A new method is presented for identifying waveforms of fluctuations in turbulent plasmas. The method is based on heartbeat analysis in which the convolution of a waveform is obtained by employing the phase tracking method. Phase tracking is performed by correlating raw time-series data with a template waveform; the template is evaluated through iteration procedure. The method is applied to fluctuations in a PANTA plasma, and the nonlinear waveform and its distribution of periods are obtained.

DOI： 10.1585/pfr.9.1201016

Language：English   Publishing type：Research paper (scientific journal)  

This conference report summarizes the contributions to and discussions at the 3rd Asia-Pacific Transport Working Group (APTWG) meeting held in Jeju-island, Korea, on 21-24 May 2013. The main objective of the meeting is to develop a predictive understanding of transport mechanisms in magnetically confined fusion plasmas. In an effort to accomplish this objective, four technical working groups were organized under the headings: (1) transport barrier formation and confinement enhancement, (2) 3D effects and Magnetohydrodynamic-turbulence interaction, (3) momentum transport and non-locality and (4) particle/impurity transport and energetic particles.

DOI： 10.1088/0029-5515/54/4/047001

Language：English   Publishing type：Research paper (scientific journal)  

The life time of trapped ion granulations (trapped ions correlated by resonance) in sheared flows is calculated. The dynamics of trapped ion granulations, in the presence of sheared flows, is formulated in terms of two point correlation function of phase space density fluctuations. The evolution equation is closed by a simplified closure calculation of the triplet term. Based on the closed equation, the life time of the relative dispersion of trapped ion granulations is calculated. The result shows that i.) a relevant time scale enters via a hybrid of decorrelation and shearing, (Δω_cν′²_y)^1/3 and ii.) small scale singularities in the absence of collisional dissipation enters through logarithmic divergence.

DOI： 10.1585/pfr.9.3403018

Language：English   Publishing type：Research paper (scientific journal)  

A theory to describe the conversion of poloidal momentum into toroidal momentum by phase space structures in trapped ion resonance driven turbulence is presented. In trapped ion resonance driven turbulence, phase space structures are expected to form and can contribute to transport by exerting dynamical friction. Toroidal momentum flux by dynamical friction is calculated. It is shown that dynamical friction exerted on trapped ion granulations can mediate momentum transfer between poloidal and toroidal flows. The conversion coefficient is calculated as measurable, which can be validated in current devices.

DOI： 10.1088/0741-3335/55/12/125001

Language：English   Publishing type：Research paper (scientific journal)  

A theory to describe the conversion of poloidal momentum into toroidal momentum by phase space structures in trapped ion resonance driven turbulence is presented. In trapped ion resonance driven turbulence, phase space structures are expected to form and can contribute to transport by exerting dynamical friction. Toroidal momentum flux by dynamical friction is calculated. It is shown that dynamical friction exerted on trapped ion granulations can mediate momentum transfer between poloidal and toroidal flows. The conversion coefficient is calculated as measurable that can be validated in present devices.

Language：English   Publishing type：Research paper (scientific journal)  

An overview of the physics of intrinsic torque is presented, with special emphasis on the phenomenology of intrinsic toroidal rotation in tokamaks, its theoretical understanding, and the variety of momentum transport bifurcation dynamics. Ohmic reversals and electron cyclotron heating-driven counter torque are discussed in some detail. Symmetry breaking by lower single null versus upper single null asymmetry is related to the origin of intrinsic torque at the separatrix.

DOI： 10.1088/0029-5515/53/10/104019

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Understanding the L → H and H → L transitions is crucial to successful ITER operation. In this paper we present novel theoretical and modelling study results on the spatio-temporal dynamics of the transition. We place a special emphasis on the role of zonal flows and the micro → macro connection between dynamics and the power threshold (P_T) dependences. The model studied evolves five coupled fields in time and one space dimension, in simplified geometry. The content of this paper is (a) the model fundamentals and the space-time evolution during the L → I → H transition, (b) the physics origin of the well-known ∇B-drift asymmetry in P_T, (c) the role of heat avalanches in the intrinsic variability of the L → H transition, (d) the dynamics of the H → L back transition and the physics of hysteresis, (e) conclusion and discussion, with a special emphasis on the implications of transition dynamics for the L → H power threshold scalings.

DOI： 10.1088/0029-5515/53/7/073044

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We discuss theoretical progress in turbulent transport modelling in tokamaks. In particular, we address issues that the conventional quasilinear type calculation cannot confront, such as (i) the nature of turbulence in the edge-core coupling region of tokamaks (i.e. the so-called 'no man's land'), and the dynamics of incoming structures coupled to zonal flows, (ii) nonlinear dynamics of zonal flows and (iii) transport by drift wave turbulence with strong wave-particle interaction. A unifying theme of these studies is their formulation in terms of the phase space density correlation evolution.

DOI： 10.1088/0029-5515/53/4/043008

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We propose a novel mechanism to describe E×B flow pattern formation based upon the dynamics of propagation of heat-flux modulations. The E×B flows of interest are staircases, which are quasiregular patterns of strong, localized shear layers and profile corrugations interspersed between regions of avalanching. An analogy of staircase formation to jam formation in traffic flow is used to develop an extended model of heat avalanche dynamics. The extension includes a flux response time, during which the instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is the counterpart of the drivers' response time in traffic, during which drivers adjust their speed to match the background traffic flow. The finite response time causes the growth of mesoscale temperature perturbations, which evolve to form profile corrugations. The length scale associated with the maximum growth rate scales as Δ2∼(v _thi/λT_i)ρ_i√χ _neoτ, where λT_i is a typical heat pulse speed, χ_neo is the neoclassical thermal diffusivity, and τ is the response time of the heat flux. The connection between the scale length Δ2 and the staircase interstep scale is discussed.

DOI： 10.1103/PhysRevLett.110.105002

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Simple flux-gradient relations that involve time delay and radial coupling are discussed. Such a formulation leads to a rather simple description of avalanches and may explain breaking of gyroBohm transport scaling. The generalization of the flux-gradient relation (i.e., constitutive relation), which involve both time delay and spatial coupling, is derived from drift-kinetic equation, leading to kinetic definitions of constitutive elements such as the flux of radial heat flux. This allows numerical simulations to compute these cubic quantities directly. The formulation introduced here can be viewed as an extension of turbulence spreading to include the effect of spreading of cross-phase as well as turbulence intensity, combined in such a way to give the flux. The link between turbulence spreading and entropy production is highlighted. An extension of this formulation to general quasi-linear theory for the distribution function in the phase space of radial position and parallel velocity is also discussed.

DOI： 10.1063/1.4792161

Language：English   Publishing type：Research paper (scientific journal)  

We characterize blob-hole structures as equilibrium solutions for potential vorticity (PV) conserving systems. To demonstrate this, we consider equilibrium statistical mechanics of PV conserving fluids. We calculate partition function and free energy of the system, under the constraints that the energy and all the moments of PV are conserved. Equilibrium solutions are obtained by minimizing the free energy. As an example of analytical solutions from this approach, we consider solutions that conserve the energy and potential enstrophy. The connection of the obtained solutions to blob-hole structures is discussed.

DOI： 10.1585/pfr.8.2403080

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

The role of turbulence driven flows in describing drift hole structure and dynamics is discussed. Turbulence driven flows enter the plasma medium response and alter drift hole structures by changing the screening length of the drift hole potential. Specifically, turbulence driven flows shift the drift hole potential radially, and absorb drift hole energy via the hole-flow resonance. It is shown that the absorption shifts the phase of a momentum flux, and so enables the irreversible coupling of drift holes to turbulence driven flows. We show that drift holes and turbulence driven flows are dynamically coupled, and self-regulate each other, so that a stationary state can be achieved with non-zero turbulence driven flows. As an application, a bound on the fluctuation amplitude in the coupled system is derived. The bound is obtained by requiring that the resultant zonal flow velocity should be smaller than the critical flow velocity for the drift hole potential to be self-bound (i.e., the velocity that the screening length be positive). The result predicts m a x 2 ∼ (ν d / ω c i) (k / k y), where zonal flow damping appears as a control parameter. The implications of this result for the problem of edge-core coupling (i.e., explaining turbulence and transport in No Man's Land) are discussed.

DOI： 10.1063/1.4737197

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

We present a theory for relaxation and transport in phase space for gyrokinetic drift wave turbulence with zonal flow. The interaction between phase space eddys and zonal flows is considered in two different limits, namely for K 1 and K ≃ 1 where K is the Kubo number. For K 1, the growth of an isolated coherent phase space structure is calculated, including the associated zonal flow dynamics. For K ≃ 1, mean field relaxation dynamics is considered in the presence of phase space granulations and zonal flows. In both limits, it is shown that the evolution equations for phase space structures are structurally similar to a corresponding Charney-Drazin theorem for zonal momentum balance in a potential vorticity conserving, quasi-geostrophic system. The transport flux in phase space is calculated in the presence of phase space density granulations and zonal flows. The zonal flow exerts a dynamical friction on ion phase space density evolution, which is a fundamentally new zonal flow effect.

DOI： 10.1063/1.3662428

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Intrinsic rotation has been observed in I-mode plasmas from the C-Mod tokamak, and is found to be similar to that in H mode, both in its edge origin and in the scaling with global pressure. Since both plasmas have similar edge T, but completely different edge n, it may be concluded that the drive of the intrinsic rotation is the edge T rather than P. Evidence suggests that the connection between gradients and rotation is the residual stress, and a scaling for the rotation from conversion of free energy to macroscopic flow is calculated.

DOI： 10.1103/PhysRevLett.106.215001

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

A theory of the efficiency of the plasma flow generation process is presented. A measure of the efficiency of plasma self-acceleration of mesoscale and mean flows from the heat flux is introduced by analogy with engines, using the entropy budget defined by thermal relaxation and flow generation. The efficiency is defined as the ratio of the entropy destruction rate due to flow generation to the entropy production rate due to ∇T relaxation (i.e., related to turbulent heat flux). The efficiencies for two different cases, i.e., for the generation of turbulent driven E×B shear flow (zonal flow) and for toroidal intrinsic rotation, are considered for a stationary state, achieved by balancing entropy production rate and destruction rate order by order in O (k_||/k_⊥), where k is the wave number. The efficiency of intrinsic toroidal rotation is derived and shown to be ^eIR ∼ (Mach)_th² ∼0.01. The scaling of the efficiency of intrinsic rotation generation is also derived and shown to be ρ*² (q²/ŝ²) (R ²/L_T²) = ρ*² (L _s²/L_T²), which suggests a machine size scaling and an unfavorable plasma current scaling which enters through the shear length.

DOI： 10.1063/1.3496055

Language：English   Publishing type：Research paper (scientific journal)  

The inviscid invariance of potential vorticity is used to derive momentum balance relations for zonal flows in drift wave turbulence. The relations are constructed by exploiting potential enstrophy balance and the Taylor identity, and link flow momentum to turbulence pseudomomentum, along with the driving flux, the dissipation and turbulence spreading. Applications to atmospheric jets and to zonal flows in plasmas are discussed.

DOI： 10.1088/0741-3335/50/12/124018

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Reviews of Modern Plasma Physics  

This memorial note for Professor Sanae-I Itoh presents her specific achievements in physics research alongside her wider record of accomplishment in the field of magnetically confined plasmas. The topics include bifurcation phenomena (e.g., H-mode and improved confinement modes), turbulence-generated structures (e.g., zonal flows and streamers), and fundamental concepts and processes in plasma turbulence (e.g. nonlinear couplings and energy transfer. The note focuses initially on results obtained through her integration of theory, simulation, and experiment, particularly those arising from a low temperature plasma facility at Kyushu University. We then describe contemporary challenges in plasma turbulence which Sanae addressed with great interest, and consider some of the perspectives that were opened by her achievements.

DOI： 10.1007/s41614-023-00123-6

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Propulsion and Power  

To understand anomalous electron transport in a Hall thruster, plasma turbulence inside the acceleration channel was observed using a 76 GHz microwave interferometer. The dependence of the amplitude of the 100–500 kHz turbulence on magnetic flux density, and the relationships between the turbulence and other plasma instabilities and between the turbulence and the discharge current were investigated through spectral density and bicoherence analysis. The amplitude of electron number density fluctuations of the turbulence, integrating the spectral density from 100 to 500 kHz, is 1017 m−3, or almost 10% of the time-averaged electron number density. The amplitude of the turbulence decreases with increase in weak magnetic field strength (coil current less than 0.6 A) and then increases with increase in magnetic field strength. The amplitude of the turbulence has a positive relation to the discharge current, leads to anomalous electron transport inside the acceleration channel, and is coupled with ionization instability. In addition, low-frequency perturbations of several hundred hertz were observed, with a positive relation to the turbulence and coupled with both ionization instability and turbulence.

DOI： 10.2514/1.B38711

Web of Science

Scopus

Event date： 2018.12

Language：Japanese  

Venue：大阪大学   Country：Japan  

Event date： 2018.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Kanazawa   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：SWIP   Country：China  

Event date： 2018.8

Language：English   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：SWIP   Country：China  

Event date： 2018.6

Language：English  

Venue：Vancouver   Country：Canada  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東海大学　湘南キャンパス   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2014.3

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東海大学　湘南キャンパス   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東海大学　湘南キャンパス   Country：Japan  

Event date： 2014.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東海大学　湘南キャンパス   Country：Japan  

Event date： 2013.11

Language：English  

Country：Japan  

Event date： 2013.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Denver, CO   Country：United States  

E × B flow patterns are often observed to self-organize in magnetized plasmas. Recently, a new class of E×B flow pattern, called an ‘E×B staircase’, was observed in a simulation study using the full-f flux driven GYSELA code. Here, E × B staircases are quasi-regular steady patterns of localized shear layers and temperature profile corrugations. The shear layers are interspaced between regions of turbulent avalanching of the size of several correlation length (∼ 10∆c). In this work, a theory to describe the formation of such E × B staircases from a bath of stochastic avalanches is presented, based on analogy of staircase formation to jam formation in traffic flow. Namely, staircase formation is viewed as a heat flux ‘jam’ that causes profile corrugation, which is analogous to a traffic jam that causes corrugations in the local car density in a traffic flow. To model such an effect in plasmas, a finite response time τ is introduced, during which instantaneous heat flux relaxes to the mean heat flux, determined by symmetry constraints. The response time introduced here is an analogue of drivers’ response time in traffic flow dynamics. It is shown that the extended model describes a heat flux ‘jam’ and profile corrugation, which appears as an instability, in analogy to the way a clustering instability leads to a traffic jam. Such local amplification of heat and profile corrugations can lead to the formation of E × B staircases. The scale length that gives the maximum growth rate falls in the mesoscale range and is comparable to the staircase step spacing.

Event date： 2013.10

Language：English  

Venue：福岡   Country：Japan  

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島   Country：Japan  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Aix-en-Provence   Country：France  

Event date： 2013.5

Language：English  

Venue：Jeju   Country：Korea, Republic of  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul   Country：Korea, Republic of  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東北大学   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：盛岡   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都市大学   Country：Japan  

磁場閉じ込め核融合研究に関する最近の研究動向について報告した。国際熱核融合炉ITERに至る道と現在の状況、最近のスタートアップの参入や研究体制の変化、最近の研究について報告した。

Language：English   Presentation type：Oral presentation (general)  

Venue：Online  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：姫路   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Aix-en-Provence   Country：France  

Language：English   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：仙台   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Kaoshung   Country：Taiwan, Province of China  

Language：English   Presentation type：Oral presentation (general)  

Venue：Kaoshung   Country：Taiwan, Province of China  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：東北学院大学   Country：Japan  

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：名古屋大学   Country：Japan  

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：名古屋大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋大学   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Nara   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Aix-en-Provence   Country：France  

Presentation type：Oral presentation (general)  

Venue：早稲田大学　東京   Country：Other  

Presentation type：Oral presentation (general)  

Venue：Niigata   Country：Other  

Presentation type：Symposium, workshop panel (public)  

Venue：Niigata   Country：Other  

Presentation type：Oral presentation (general)  

Venue：Toki   Country：Other  

Venue：St. Petersburg   Country：Russian Federation  

Presentation type：Oral presentation (general)  

Venue：ハルビン   Country：China  

Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Other  

Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Other  

Language：Japanese  

Venue：東京   Country：Japan  

Language：Japanese  

Venue：東京   Country：Japan  

Language：Japanese  

Venue：東京   Country：Japan  

Language：English  

Venue：Toki   Country：Japan  

Language：English  

Venue：Fukuoka   Country：Japan  

Language：English  

Venue：Fukuoka   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：徳島   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Type：Competition, symposium, etc. 

Number of participants：30

Type：Competition, symposium, etc. 

Number of participants：30

Type：Competition, symposium, etc. 

Number of participants：30