Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Yusuke Kosuga Last modified date:2020.05.20

Associate Professor / Division of Nuclear Fusion Dynamics / Research Institute for Applied Mechanics


Papers
1. P. H. Diamond, O. D. Gurcan, T. S. Hahm, K. Miki, Y. Kosuga, X. Garbet, Momentum theorems and the structure of atmospheric jets and zonal flows in plasmas, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/50/12/124018, 50, 12, 2008.12, 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..
2. Y. Kosuga, P. H. Diamond, Ö D. Gürcan, On the efficiency of intrinsic rotation generation in tokamaks, Physics of Plasmas, 10.1063/1.3496055, 17, 10, 2010.10, 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 (q22) (R 2/LT2) = ρ*2 (L s2/LT2), which suggests a machine size scaling and an unfavorable plasma current scaling which enters through the shear length..
3. J. E. Rice, J. W. Hughes, P. H. Diamond, Y. Kosuga, Y. A. Podpaly, M. L. Reinke, M. J. Greenwald, D. Gürcan, T. S. Hahm, A. E. Hubbard, E. S. Marmar, C. J. McDevitt, D. G. Whyte, Edge temperature gradient as intrinsic rotation drive in alcator C-Mod tokamak plasmas, Physical Review Letters, 10.1103/PhysRevLett.106.215001, 106, 21, 2011.05, 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..
4. Y. Kosuga, P. H. Diamond, On relaxation and transport in gyrokinetic drift wave turbulence with zonal flow, Physics of Plasmas, 10.1063/1.3662428, 18, 12, 2011.12, 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..
5. Y. Kosuga, P. H. Diamond, Drift hole structure and dynamics with turbulence driven flows, Physics of Plasmas, 10.1063/1.4737197, 19, 7, 2012.07, 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..
6. Yusuke Kosuga, Patrick H. Diamond, Blob-hole structures as non-axisymmetric equilibrium solutions for potential vorticity conserving fluids, Plasma and Fusion Research, 10.1585/pfr.8.2403080, 8, 2013.01, 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..
7. Ö D. Gürcan, P. H. Diamond, X. Garbet, V. Berionni, G. Dif-Pradalier, P. Hennequin, P. Morel, Y. Kosuga, L. Vermare, Transport of radial heat flux and second sound in fusion plasmas, Physics of Plasmas, 10.1063/1.4792161, 20, 2, 2013.02, 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..
8. Y. Kosuga, P. H. Diamond, O. D. Gürcan, How the propagation of heat-flux modulations triggers E×B flow pattern formation, Physical review letters, 10.1103/PhysRevLett.110.105002, 110, 10, 2013.03, 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/λTii√χ neoτ, where λTi is a typical heat pulse speed, χneo 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..
9. Y. Kosuga, P. H. Diamond, L. Wang, Ö D. Gürcan, T. S. Hahm, Progress on theoretical issues in modelling turbulent transport, Nuclear Fusion, 10.1088/0029-5515/53/4/043008, 53, 4, 2013.04, 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..
10. K. Miki, P. H. Diamond, N. Fedorczak, Ö D. Gürcan, M. Malkov, C. Lee, Y. Kosuga, G. Tynan, G. S. Xu, T. Estrada, D. McDonald, L. Schmitz, K. J. Zhao, Spatio-temporal evolution of the L → H and H → L transitions, Nuclear Fusion, 10.1088/0029-5515/53/7/073044, 53, 7, 2013.07, 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 (PT) 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 PT, (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..
11. P. H. Diamond, Y. Kosuga, O. D. Gürcan, C. J. McDevitt, T. S. Hahm, N. Fedorczak, J. E. Rice, W. X. Wang, S. Ku, J. M. Kwon, G. Dif-Pradalier, J. Abiteboul, L. Wang, W. H. Ko, Y. J. Shi, K. Ida, W. Solomon, H. Jhang, S. S. Kim, S. Yi, S. H. Ko, Y. Sarazin, R. Singh, C. S. Chang, An overview of intrinsic torque and momentum transport bifurcations in toroidal plasmas, Nuclear Fusion, 10.1088/0029-5515/53/10/104019, 53, 10, 2013.10, 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..
12. Y. Kosuga, S. I. Itoh, P. H. Diamond, K. Itoh, Conversion of poloidal flows into toroidal flows by phase space structures in trapped ion resonance driven turbulence, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/55/12/125001, 55, 12, 2013.12, 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..
13. Hogun Jhang, P. H. Diamond, M. Leconte, K. Ida, J. M. Kwon, N. Tamura, Yusuke Kosuga, The 3rd Asia-Pacific Transport Working Group (APTWG) Meeting, Nuclear Fusion, 10.1088/0029-5515/54/4/047001, 54, 4, 2014.01, 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..
14. Yusuke Kosuga, Sanae I. Itoh, Patrick H. Diamond, Kimitaka Itoh, Maxime Lesur, Relative dispersion of trapped ion granulations in sheared flows, Plasma and Fusion Research, 10.1585/pfr.9.3403018, 9, SPECIALISSUE.2, 2014.01, 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, (Δωcν′2y)1/3 and ii.) small scale singularities in the absence of collisional dissipation enters through logarithmic divergence..
15. Shigeru Inagaki, Yudai Miwa, Tatsuya Kobayashi, Takuma Yamada, Yoshihiko Nagashima, Tomohiro Mitsuzono, Hiromitsu Fujino, Makoto Sasaki, Naohiro Kasuya, Maxime Lesur, Yusuke Kosuga, Akihide Fujisawa, Sanae I. Itoh, Kimitaka Itoh, Identification of quasi-periodic nonlinear waveforms in turbulent plasmas, Plasma and Fusion Research, 10.1585/pfr.9.1201016, 9, 2014.01, 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..
16. Z. B. Guo, P. H. Diamond, Y. Kosuga, Ö D. Gürcan, Elasticity in drift-wave-zonal-flow turbulence, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.89.041101, 89, 4, 2014.04, 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..
17. Y. Kosuga, P. H. Diamond, G. Dif-Pradalier, O. D. Gürcan, E × B shear pattern formation by radial propagation of heat flux waves, Physics of Plasmas, 10.1063/1.4872018, 21, 5, 2014.05, 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..
18. M. Lesur, P. H. Diamond, Y. Kosuga, Nonlinear current-driven ion-acoustic instability driven by phase-space structures, Plasma Physics and Controlled Fusion, 10.1088/0741-3335/56/7/075005, 56, 7, 2014.07, 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..
19. Z. B. Guo, P. H. Diamond, Y. Kosuga, Ö D. Gürcan, Turbulence elasticity - A new mechanism for transport barrier dynamics, Physics of Plasmas, 10.1063/1.4894695, 21, 9, 2014.09, 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 Δωk is the local turbulence decorrelation rate and τcr is the threshold delay time. In the basic predator-prey feedback system, τcr 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..
20. Y. Kosuga, S. I. Itoh, P. H. Diamond, K. Itoh, M. Lesur, Ion temperature gradient driven turbulence with strong trapped ion resonance, Physics of Plasmas, 10.1063/1.4897179, 21, 10, 2014.10, 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..
21. M. Lesur, P. H. Diamond, Y. Kosuga, Phase-space jets drive transport and anomalous resistivity, Physics of Plasmas, 10.1063/1.4902525, 21, 11, 2014.11, 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..
22. Takuma Yamada, Inagaki Shigeru, T. Kobayashi, Yoshihiko Nagashima, T. Mitsuzono, Y. Miwa, K. Nakanishi, H. Fujino, Makoto Sasaki, Naohiro Kasuya, M. Lesur, Yusuke Kosuga, akihide fujisawa, Sanae Itoh, K. Itoh, End plate biasing experiments in linear magnetized plasmas, Nuclear Fusion, 10.1088/0029-5515/54/11/114010, 54, 11, 2014.11, 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..
23. K. Ida, Z. Shi, H. J. Sun, S. Inagaki, K. Kamiya, J. E. Rice, N. Tamura, P. H. Diamond, G. Dif-Pradalier, X. L. Zou, K. Itoh, S. Sugita, O. D. Gürcan, T. Estrada, C. Hidalgo, T. S. Hahm, A. Field, X. T. Ding, Y. Sakamoto, S. Oldenbürger, M. Yoshinuma, T. Kobayashi, M. Jiang, S. H. Hahn, Y. M. Jeon, S. H. Hong, Y. Kosuga, J. Dong, S. I. Itoh, Towards an emerging understanding of non-locality phenomena and non-local transport, Nuclear Fusion, 10.1088/0029-5515/55/1/013022, 55, 1, 2015.01, 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.
24. Shigeru Inagaki, Kimitaka Itoh, Sanae I. Itoh, Yusuke Kosuga, Maxime Lesur, Naohiro Kasuya, Test of the telegraph equation for transport dynamics in plasma, Plasma and Fusion Research, 10.1585/pfr.10.1203002, 10, 2015, 1-2, 2015.01, 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..
25. Fumiyoshi Kin, Takuma Yamada, Shigeru Inagaki, Hiroyuki Arakawa, Yoshihiko Nagashima, Naohiro Kasuya, Akihide Fujisawa, Kousuke Nakanishi, Hikaru Kono, Takaaki Mizokami, Makoto Sasaki, Maxime Lesur, Yusuke Kosuga, Kimitaka Itoh, Sanae I. Itoh, Evaluation of non-linear mode coupling during end-plate biasing experiment in PANTA, Plasma and Fusion Research, 10.1585/pfr.10.3401043, 10, 2015.01, 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..
26. Yusuke Kosuga, Sanae I. Itoh, Kimitaka Itoh, Density peaking by parallel flow shear driven instability, Plasma and Fusion Research, 10.1585/pfr.10.3401024, 10, 2015.01, 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..
27. K. Ida, J. M. Kwon, M. Leconte, W. H. Ko, S. Inagaki, Y. Todo, Y. Kosuga, APTWG
The 4th Asia-Pacific Transport Working Group Meeting, Nuclear Fusion, 10.1088/0029-5515/55/1/017001, 55, 1, 2015.01, 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..
28. G. Dif-Pradalier, G. Hornung, Ph Ghendrih, Y. Sarazin, F. Clairet, L. Vermare, P. H. Diamond, J. Abiteboul, T. Cartier-Michaud, C. Ehrlacher, D. Estève, X. Garbet, V. Grandgirard, O. D. Gürcan, P. Hennequin, Y. Kosuga, G. Latu, P. Maget, P. Morel, C. Norscini, R. Sabot, A. Storelli, Finding the Elusive E×B Staircase in Magnetized Plasmas, Physical review letters, 10.1103/PhysRevLett.114.085004, 114, 8, 2015.02, 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..
29. Z. B. Guo, P. H. Diamond, Y. Kosuga, D. Gürcan, Turbulence elasticity
A key concept to a unified paradigm of L→I→H transition, Nuclear Fusion, 10.1088/0029-5515/55/4/043022, 55, 4, 2015.04, 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|/Δωk1, with |V′ZF| the ZF shearing rate and Δωk 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 Δωk<|V′ZF|cr, where V′cr is a critical flow shearing rate and is derived explicitly. If |V′E×B|>V′cr (VEB is mean E×B shear flow driven by edge radial electrostatic field), the I-mode will terminate and spiral into the H-mode..
30. T. Kobayashi, S. Inagaki, M. Sasaki, Y. Kosuga, H. Arakawa, T. Yamada, Y. Nagashima, Y. Miwa, N. Kasuya, A. Fujisawa, S. I. Itoh, K. Itoh, Azimuthal inhomogeneity of turbulence structure and its impact on intermittent particle transport in linear magnetized plasmas, Physics of Plasmas, 10.1063/1.4934537, 22, 11, 2015.11, 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..
31. Tomotsugu Kanzaki, Yoshihiko Nagashima, Shigeru Inagaki, Fumiyoshi Kin, Yudai Miwa, Makoto Sasaki, Takuma Yamada, Akihide Fujisawa, Tatsuya Kobayashi, Naohiro Kasuya, Yusuke Kosuga, Sanae I. Itoh, Kimitaka Itoh, Improvement of the reynolds stress probe for end-plate biasing experiments in a cylindrical laboratory plasma, Plasma and Fusion Research, 10.1585/pfr.11.1201091, 11, 2016.01, 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..
32. Yusuke Kosuga, Sanae I. Itoh, Kimitaka Itoh, Flux of parallel flow momentum by parallel shear flow driven instability, Plasma and Fusion Research, 10.1585/pfr.11.1203018, 11, 2016.01, 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: vD1 ~ v˜x2/γ(0) and vD2 ~ 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 vD2 is important around the marginal state. Since typically vD1 ≫ vD2 ~ Dn, where Dn is the particle diffusivity, the Prandtl number (≡ v/Dn) 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..
33. Kimitaka Itoh, Kaijun Zhao, Jiaqi Dong, Sanae I. Itoh, Akihide Fujisawa, Shigeru Inagaki, Makoto Sasaki, Yoshihiko Nagashima, Yusuke Kosuga, Jun Cheng, Tatsuya Kobayashi, A calibration of setting of mach probes by observing GAM oscillations, Plasma and Fusion Research, 10.1585/pfr.11.1402002, 11, 2016.01, 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..
34. S. Inagaki, T. Kobayashi, Y. Kosuga, S. I. Itoh, T. Mitsuzono, Y. Nagashima, H. Arakawa, T. Yamada, Y. Miwa, N. Kasuya, M. Sasaki, M. Lesur, A. Fujisawa, K. Itoh, A Concept of Cross-Ferroic Plasma Turbulence, Scientific reports, 10.1038/srep22189, 6, 2016.02, 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..
35. M. Lesur, K. Itoh, T. Ido, S. I. Itoh, Y. Kosuga, M. Sasaki, S. Inagaki, M. Osakabe, K. Ogawa, A. Shimizu, K. Ida, Nonlinear excitation of subcritical fast ion-driven modes, Nuclear Fusion, 10.1088/0029-5515/56/5/056009, 56, 5, 2016.04, 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..
36. K. Itoh, Sanae Itoh, Y. Kosuga, M. Lesur, T. Ido, Onset condition of the subcritical geodesic acoustic mode instability in the presence of energetic-particle-driven geodesic acoustic mode, Plasma Physics Reports, 10.1134/S1063780X16050056, 42, 5, 418-423, 2016.05, 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..
37. Y. Kosuga, S. I. Itoh, K. Itoh, Turbulence Dynamics with the Coupling of Density Gradient and Parallel Velocity Gradient in the Edge Plasmas, Contributions to Plasma Physics, 10.1002/ctpp.201610047, 56, 6-8, 511-515, 2016.08, 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. (.
38. K. J. Zhao, Y. Nagashima, P. H. Diamond, J. Q. Dong, K. Itoh, S. I. Itoh, L. W. Yan, J. Cheng, A. Fujisawa, S. Inagaki, Y. Kosuga, M. Sasaki, Z. X. Wang, L. Wei, Z. H. Huang, D. L. Yu, W. Y. Hong, Q. Li, X. Q. Ji, X. M. Song, Y. Huang, Yi Liu, Q. W. Yang, X. T. Ding, X. R. Duan, Synchronization of Geodesic Acoustic Modes and Magnetic Fluctuations in Toroidal Plasmas, Physical review letters, 10.1103/PhysRevLett.117.145002, 117, 14, 2016.09, 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..
39. Kimitaka Itoh, Sanae I. Itoh, Katsumi Ida, Yusuke Kosuga, On magnetic signals of a large-scale quasi-electrostatic perturbation, journal of the physical society of japan, 10.7566/JPSJ.85.094504, 85, 9, 2016.09, 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..
40. H. Arakawa, S. Inagaki, M. Sasaki, Y. Kosuga, T. Kobayashi, N. Kasuya, Y. Nagashima, T. Yamada, M. Lesur, A. Fujisawa, K. Itoh, S. I. Itoh, Eddy, drift wave and zonal flow dynamics in a linear magnetized plasma, Scientific reports, 10.1038/srep33371, 6, 2016.09, 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..
41. Fumiyoshi Kin, Takuma Yamada, Shigeru Inagaki, Yoshihiko Nagashima, Hiroyuki Arakawa, Tatsuya Kobayashi, Yudai Miwa, Naohiro Kasuya, Makoto Sasaki, Yusuke Kosuga, Akihide Fujisawa, Kimitaka Itoh, Sanae I. Itoh, Changes of particle flux during end-plate biasing experiment in PANTA, journal of the physical society of japan, 10.7566/JPSJ.85.093501, 85, 9, 2016.09, 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..
42. T. Kobayashi, S. Inagaki, Y. Kosuga, M. Sasaki, Y. Nagashima, T. Yamada, H. Arakawa, N. Kasuya, A. Fujisawa, S. I. Itoh, K. Itoh, Structure formation in parallel ion flow and density profiles by cross-ferroic turbulent transport in linear magnetized plasma, Physics of Plasmas, 10.1063/1.4965915, 23, 10, 2016.10, 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..
43. M. Sasaki, N. Kasuya, K. Itoh, K. Hallatschek, M. Lesur, Y. Kosuga, S. I. Itoh, A branch of energetic-particle driven geodesic acoustic modes due to magnetic drift resonance, Physics of Plasmas, 10.1063/1.4963397, 23, 10, 2016.10, 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..
44. Tatsuya Kobayashi, Sigeru Inagaki, Makoto Sasaki, Yusuke Kosuga, Hiroyuki Arakawa, Fumiyoshi Kin, Takuma Yamada, Yoshihiko Nagashima, Naohiro Kasuya, Akihide Fujisawa, Sanae I. Itoh, Kimitaka Itoh, Phenomenological classification of turbulence states in linear magnetized plasma PANTA, Plasma and Fusion Research, 10.1585/pfr.12.1401019, 12, 2017.01, 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..
45. Sanae I. Itoh, Kimitaka Itoh, Yoshihiko Nagashima, Yusuke Kosuga, On the application of cross bispectrum and cross bicoherence, Plasma and Fusion Research, 10.1585/pfr.12.1101003, 12, 2017.01, 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..
46. Kazunobu Hasamada, Yusuke Kosuga, Fumiyoshi Kin, Sigeru Inagaki, Yoshihiko Nagashima, Tatsuya Kobayashi, Makoto Sasaki, Naohiro Kasuya, Kotaro Yamasaki, Sanae I. Itoh, Kimitaka Itoh, Akihide Fujisawa, Nonlinear coupling of driftwaves and high frequency fluctuation on PANTA, Plasma and Fusion Research, 10.1585/pfr.12.1201034, 12, 2017.01, 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..
47. Makoto Sasaki, Naohiro Kasuya, Shinichiro Toda, Takuma Yamada, Yusuke Kosuga, Hiroyuki Arakawa, Tatsuya Kobayashi, Shigeru Inagaki, Akihide Fujisawa, Yoshihiko Nagashima, Kimitaka Itoh, Sanae I. Itoh, Multiple-instabilities in magnetized plasmas with density gradient and velocity shears, Plasma and Fusion Research, 10.1585/pfr.12.1401042, 12, 2017.01, 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..
48. Nathan Dupertuis, Shigeru Inagaki, Yoshihiko Nagashima, Yusuke Kosuga, Fumiyoshi Kin, Tatsuya Kobayashi, Naohiro Kasuya, Makoto Sasaki, Akihide Fujisawa, Minh Quang Tran, Sanae I. Itoh, Kimitaka Itoh, Coexistence of driftwaves and d'angelo modes at different position and frequency in linear plasma device, Plasma and Fusion Research, 10.1585/pfr.12.1201008, 12, 2017.01, 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..
49. M. Lesur, T. Cartier-Michaud, T. Drouot, P. H. Diamond, Y. Kosuga, T. Réveillé, E. Gravier, X. Garbet, S. I. Itoh, K. Itoh, A simple model for electron dissipation in trapped ion turbulence, Physics of Plasmas, 10.1063/1.4974269, 24, 1, 2017.01, 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..
50. Y. Kosuga, S. I. Itoh, K. Itoh, Zonal flow generation in parallel flow shear driven turbulence, Physics of Plasmas, 10.1063/1.4978485, 24, 3, 2017.03, 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..
51. M. Sasaki, N. Kasuya, K. Itoh, Y. Kosuga, M. Lesur, K. Hallatschek, S. I. Itoh, Toroidal momentum channeling of geodesic acoustic modes driven by fast ions, Nuclear Fusion, 10.1088/1741-4326/aa4eb4, 57, 3, 2017.03, 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..
52. Kimitaka Itoh, Sanae I. Itoh, Yoshihiko Nagashima, Takuma Yamada, Yusuke Kosuga, Akihide Fujisawa, Symmetry-breaking of turbulence structure and position identification in toroidal plasmas, Plasma and Fusion Research, 10.1585/PFR.13.1102113, 13, 2018.01, 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..
53. Yuichi Kawachi, Sigeru Inagaki, Kentaro Tomita, Kotaro Yamasaki, Fumiyoshi Kin, Yusuke Kosuga, Makoto Sasaki, Yoshihiko Nagashima, Naohiro Kasuya, Kazunobu Hasamada, Boyu Zhang, Akihide Fujisawa, Determination of spatiotemporal structure of fluctuations by statistical averaging method, Plasma and Fusion Research, 10.1585/PFR.13.3401105, 13, 2018.01, 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..
54. Makoto Sasaki, Naohiro Kasuya, Yusuke Kosuga, Tatsuya Kobayashi, Takuma Yamada, Hiroyuki Arakawa, Shigeru Inagaki, Kimitaka Itoh, Turbulence simulation on zonal flow formations in the presence of parallel flows, Plasma and Fusion Research, 10.1585/PFR.14.1401161, 14, 2019.01, 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..
55. Yuichi Kawachi, Sigeru Inagaki, Kazunobu Hasamada, Kotaro Yamasaki, Fumiyoshi Kin, Yusuke Kosuga, Makoto Sasaki, Yoshihiko Nagashima, Naohiro Kasuya, Takuma Yamada, Boyu Zhang, Akihide Fujisawa, Estimation of particle flux driven by coherent mode using of statistical conditional averaging, Plasma and Fusion Research, 10.1585/PFR.14.1402090, 14, 2019.01, 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..
56. M. Sasaki, K. Itoh, Y. Kosuga, J. Q. Dong, S. Inagaki, T. Kobayashi, J. Cheng, K. J. Zhao, S. I. Itoh, Parallel flow driven instability due to toroidal return flow in high-confinement mode plasmas, Nuclear Fusion, 10.1088/1741-4326/ab1292, 59, 6, 2019.05, 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..
57. K. Yamasaki, A. Fujisawa, Y. Nagashima, C. Moon, S. Inagaki, N. Kasuya, Y. Kosuga, M. Sasaki, T. Yamada, Fourier-rectangular function analysis for cylindrical plasma images, Journal of Applied Physics, 10.1063/1.5108717, 126, 4, 2019.07, 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..
58. Hirotyuki Arakawa, Shigeru Inagaki, Yusuke Kosuga, Makoto Sasaki, Fumiyoshi Kin, Kazunobu Hasamada, Kotaro Yamasaki, Tatsuya Kobayashi, Takuma Yamada, Yoshihiko Nagashima, Akihide Fujisawa, Naohiro Kasuya, Kimitaka Itoh, Sanae I. Itoh, Ion temperature measurement by laser-induced fluorescence spectroscopy in panta, IEEJ Transactions on Electrical and Electronic Engineering, 10.1002/tee.22962, 14, 10, 1450-1454, 2019.10, 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, Ti/Te, was evaluated to be ∼0.1. The result is valuable for evaluating the nonlinear processes of the plasma turbulence..
59. Y. Kosuga, F. Kin, M. Sasaki, Scrape-off layer width set by non-linear streamer flows in drift wave turbulence, Contributions to Plasma Physics, 10.1002/ctpp.201900141, 2020.01, 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..
60. J. Cheng, J. Q. Dong, K. Itoh, S. I. Itoh, L. W. Yan, J. Q. Xu, M. Jiang, Z. H. Huang, K. J. Zhao, Z. B. Shi, W. L. Zhong, S. Inagaki, T. Kobayashi, K. Ida, Y. Kosuga, M. Sasaki, M. K. Han, Z. X. Wang, M. Xu, Y. Xu, Formation of radially elongated flow leading to onset of type-III edge localized modes in toroidal plasmas, Nuclear Fusion, 10.1088/1741-4326/ab742a, 60, 4, 2020.01, 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..
61. Y. Kosuga, M. Sasaki, Z. B. Guo, Flow helicity of wavy plasma turbulence, Physics of Plasmas, 10.1063/1.5121351, 27, 2, 2020.02, 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..
62. H. Arakawa, Makoto Sasaki, Inagaki Shigeru, Yusuke Kosuga, T. Kobayashi, Naohiro Kasuya, Takuma Yamada, Yoshihiko Nagashima, F. Kin, akihide fujisawa, K. Itoh, S. I. Itoh, Roles of solitary eddy and splash in drift wave-zonal flow system in a linear magnetized plasma, Physics of Plasmas, 10.1063/1.5094577, 26, 5, 2019.05, 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..
63. F. Kin, akihide fujisawa, K. Itoh, Yusuke Kosuga, Makoto Sasaki, Inagaki Shigeru, Yoshihiko Nagashima, Takuma Yamada, Naohiro Kasuya, K. Yamasaki, K. Hasamada, B. Y. Zhang, Y. Kawachi, H. Arakawa, T. Kobayashi, S. I. Itoh, Observations of radially elongated particle flux induced by streamer in a linear magnetized plasma, Physics of Plasmas, 10.1063/1.5093218, 26, 4, 2019.04, 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..
64. Yusuke Kosuga, K. Hasamada, Role of density modulation in driving nonlinear streamer flows in drift wave turbulence, Physics of Plasmas, 10.1063/1.5049726, 25, 10, 2018.10, 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..
65. Yusuke Kosuga, Helical flow structures in torus plasmas, Front-runners� Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 2018 Front-runners' Symposium on Plasma Physics in Honor of Professors Kimitaka Itoh and Sanae-I. Itoh, 10.1063/1.5048719, 2018.08, 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..
66. F. Kin, K. Itoh, akihide fujisawa, Yusuke Kosuga, Makoto Sasaki, Takuma Yamada, Inagaki Shigeru, Sanae Itoh, T. Kobayashi, Yoshihiko Nagashima, Naohiro Kasuya, H. Arakawa, K. Yamasaki, K. Hasamada, Extraction of nonlinear waveform in turbulent plasma, Physics of Plasmas, 10.1063/1.5027124, 25, 6, 2018.06, 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..
67. Makoto Sasaki, T. Kobayashi, K. Itoh, Naohiro Kasuya, Yusuke Kosuga, akihide fujisawa, Sanae Itoh, Spatio-temporal dynamics of turbulence trapped in geodesic acoustic modes, Physics of Plasmas, 10.1063/1.5008541, 25, 1, 2018.01, 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..
68. Takuma Yamada, Inagaki Shigeru, Makoto Sasaki, Yoshihiko Nagashima, Fumiyoshi Kin, Hiroyuki Arakawa, Tatsuya Kobayashi, Kotaro Yamasaki, Naohiro Kasuya, Yusuke Kosuga, akihide fujisawa, Kimitaka Itoh, Sanae Itoh, Three-dimensional structure of the streamer in linear plasmas, Journal of the Physical Society of Japan, 10.7566/JPSJ.87.034501, 87, 3, 2018.01, 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..
69. F. Kin, akihide fujisawa, K. Itoh, Yusuke Kosuga, Makoto Sasaki, Takuma Yamada, Inagaki Shigeru, S. I. Itoh, T. Kobayashi, Yoshihiko Nagashima, Naohiro Kasuya, H. Arakawa, K. Yamasaki, K. Hasamada, Nonlinear characteristics of mediator and streamer in linear magnetized plasmas, 45th EPS Conference on Plasma Physics, EPS 2018 45th EPS Conference on Plasma Physics, EPS 2018, 565-568, 2018.01.
70. Makoto Sasaki, T. Kobayashi, K. Itoh, Naohiro Kasuya, Yusuke Kosuga, akihide fujisawa, Inagaki Shigeru, S. I. Itoh, Spatio-temporal dynamics of turbulence coupling with zonal flows, 45th EPS Conference on Plasma Physics, EPS 2018 45th EPS Conference on Plasma Physics, EPS 2018, 449-452, 2018.01.
71. Makoto Sasaki, K. Itoh, K. Hallatschek, Naohiro Kasuya, M. Lesur, Yusuke Kosuga, Sanae Itoh, Enhancement and suppression of turbulence by energetic-particle-driven geodesic acoustic modes, Scientific Reports, 10.1038/s41598-017-17011-y, 7, 1, 2017.12, 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..
72. Yusuke Kosuga, How pattern is selected in drift wave turbulence
Role of parallel flow shear, Physics of Plasmas, 10.1063/1.5001857, 24, 12, 2017.12, 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..
73. Makoto Sasaki, Naohiro Kasuya, K. Itoh, S. Toda, Takuma Yamada, Yusuke Kosuga, Yoshihiko Nagashima, T. Kobayashi, H. Arakawa, K. Yamasaki, akihide fujisawa, Inagaki Shigeru, Sanae Itoh, Topological bifurcation of helical flows in magnetized plasmas with density gradient and parallel flow shear, Physics of Plasmas, 10.1063/1.5000343, 24, 11, 2017.11, 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..
74. K. J. Zhao, Yoshihiko Nagashima, F. M. Li, Yuejiang Shi, P. H. Diamond, J. Q. Dong, K. Itoh, Sanae Itoh, G. Zhuang, H. Liu, Z. P. Chen, J. Cheng, L. Nie, Y. H. Ding, Q. M. Hu, Z. Y. Chen, B. Rao, Z. F. Cheng, L. Gao, X. Q. Zhang, Z. J. Yang, N. C. Wang, L. Wang, W. Jin, W. Yan, J. Q. Xu, Y. F. Wu, L. W. Yan, akihide fujisawa, Inagaki Shigeru, Yusuke Kosuga, Makoto Sasaki, Temporal-spatial structures of plasmas flows and turbulence around tearing mode islands in the edge tokamak plasmas, Nuclear Fusion, 10.1088/1741-4326/aa8341, 57, 12, 2017.09, 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..
75. K. Itoh, Sanae Itoh, K. Ida, Inagaki Shigeru, Y. Kamada, K. Kamiya, J. Q. Dong, C. Hidalgo, T. Evans, W. H. Ko, H. Park, T. Tokuzawa, S. Kubo, T. Kobayashi, Yusuke Kosuga, Makoto Sasaki, G. S. Yun, S. D. Song, Naohiro Kasuya, Yoshihiko Nagashima, C. Moon, M. Yoshinuma, R. Makino, T. Tsujimura, H. Tsuchiya, U. Stroth, Hysteresis and fast timescales in transport relations of toroidal plasmas, Nuclear Fusion, 10.1088/1741-4326/aa796a, 57, 10, 2017.07, 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..
76. J. E. Rice, J. W. Hughes, P. H. Diamond, N. Cao, M. A. Chilenski, A. E. Hubbard, J. H. Irby, Yusuke Kosuga, Y. Lin, I. W. Metcalf, M. L. Reinke, E. A. Tolman, M. M. Victora, S. M. Wolfe, S. J. Wukitch, On the p scaling of intrinsic rotation in C-Mod plasmas with edge transport barriers, Nuclear Fusion, 10.1088/1741-4326/aa7b44, 57, 11, 2017.07, 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 Mi ≃= -rfpag∗/2Ls/LT∇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..
77. , K. J. Zhao, Y. Nagashima, Yoshihiko Nagashima, J. Q. Dong, K. Itoh, S. I. Itoh, Sanae Itoh, J. Cheng, A. Fujisawa, akihide fujisawa, Inagaki Shigeru, Yusuke Kosuga, Makoto Sasaki, D. L. Yu, Q. Li, X. Q. Ji, X. M. Song, Y. Huang, Yi Liu, Q. W. Yang, X. T. Ding, X. R. Duan, Mesoscale electric fluctuations interacting with zonal flows, magnetic fluctuations and turbulence, Nuclear Fusion, 10.1088/1741-4326/aa6f35, 57, 7, 2017.06, 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..
78. T. Ido, K. Itoh, M. Lesur, M. Osakabe, A. Shimizu, K. Ogawa, M. Nishiura, I. Yamada, R. Yasuhara, Yusuke Kosuga, Makoto Sasaki, K. Ida, Inagaki Shigeru, Sanae Itoh, Observation of subcritical geodesic acoustic mode excitation in the large helical device, Nuclear Fusion, 10.1088/1741-4326/aa665a, 57, 7, 2017.04, 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..
79. K. Itoh, Sanae Itoh, Makoto Sasaki, Yusuke Kosuga, Effects of hydrogen isotope in coupling between confinement, wall material and SoL turbulence, Nuclear Fusion, 10.1088/1741-4326/aa65eb, 57, 5, 2017.03, 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..
80. Yusuke Kosuga, Sanae Itoh, P. H. Diamond, K. Itoh, How turbulence fronts induce plasma spin-up, Physical Review E, 10.1103/PhysRevE.95.031203, 95, 3, 2017.03, 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..
81. Yusuke Kosuga, Sanae Itoh, P. H. Diamond, K. Itoh, M. Lesur, Role of phase space structures in collisionless drift wave turbulence and impact on transport modeling, Nuclear Fusion, 10.1088/1741-4326/57/7/072006, 57, 7, 2017.03, 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..
82. Y. Kosuga, S.-I. Itoh and K. Itoh, Zonal flow generation in parallel flow shear driven turbulence, Phys. Plasmas, 24, 032304, 2017.01.
83. Y. Kosuga, S.-I. Itoh, P.H. Diamond, K. Itoh, and M. Lesur, Role of phase space structures
in collisionless drift wave turbulence and impact on transport modeling, Nucl. Fusion, 57, 072006, 2017.01, 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..
84. Y. Kosuga, S.-I. Itoh, P.H. Diamond, K. Itoh, How turbulence fronts induce plasma spin-up, Phys. Rev. E, 95, 031203(R), 2017.01.
85. Y. Kosuga, S.-I. Itoh and K. Itoh, Evaluation of nonlinear mode coupling during end plate biasing experiment in PANTA, Plasma Fusion Res., 10, 3401043-1-3401043-1, 2015.04.
86. F. Kin, T. Yamada, S. Inagaki, H. Arakawa, Y. Nagashima, N. Kasuya, A. Fujisawa, K. Nakaganishi, H. Kono, T. Mizokami, M. Sasaki, M. Lesur, Y. Kosuga, K. Itoh, and S.-I. Itoh, Density peaking by parallel flow shear driven instability, Plasma Fusion Res., 10, 3401024-1-3401024-7, 2015.04.
87. Z. Guo, P.H. Diamond, Y. Kosuga, O.D. Gurcan, Turbulence elasticity: a key concept to univfied paradigm of L→I→H transition, Nucl. Fusion, 55, 043022-1-043022-4, 2015.03.
88. G. Dif-Pradalier, G. Hornung, Ph. Ghendrih, Y. Sarazin, F. Clairet, L. Vermore, P.H. Diamond, J. Abiteboul, T. Cartier-Michaud, C. Ehrlacher, D. Esteve, X. Garbet, V. Grand- girard, O.D. Gurcan, P. Hennequin, Y. Kosuga, G. Latu, P. Maget, P. Morel, C. Norscini, R. Sabot, and A. Storelli, Finding the Elusive E × B staircase in magnetized plasmas, Phys. Rev. Lett., 114, 085004-1-085004-5, 2015.02.
89. K. Ida, Z. Shi, H.J. Sun, S. Inagaki, K. Kamiya, J.E. Rice, N. Tamura, P.H. Diamond, G. Dif-Pradalier, X.L. Zou, K. Itoh, S. Sugita, O ̈.D. Gu ̈rcan, T. Estrada, C. Hidalgo, T.S. Hahm, A. Field, X.T. Ding, Y. Sakamoto, S. Oldenburger, M. Yoshinuma, T. Kobayashi, M. Jiang, S.H. Hahn, Y.M. Jeon, S.H. Hong, Y. Kosuga, J. Dong and S.-I. Itoh, Towards an emerging understanding of non-local phenomena and non-local transport, Nucl. Fusion, 55, 013022-1-013022-19, 2015.01.
90. S. Inagaki, K. Itoh, S.-I. Itoh, Y. Kosuga, M. Lesur, and N. Kasuya, Test of the Telegraph Equation for Transport Dynamics in Plasma, Plasma Fusion Res., 10, 1203002-1-1203002-2, 2015.01.
91. K. Ida, J.M. Kwon, M. Leconte, W.H. Ko, S. Inagaki, Y. Todo, and Y. Kosuga, The 4th Asia-Pacific transport working group (APTWG) meeting, Nucl. Fusion, 55, 017001-1-017001-10, 2014.12.
92. T. Yamada, S. Inagaki, T. Kobayashi, Y. Nagashima, T. Mitsuzono, Y. Miwa, K. Nakanishi, H. Fujino, M. Sasaki, N. Kasuya, M. Lesur, Y. Kosuga, A. Fujisawa, S.-I. Itoh, and K. Itoh, End plate biasing experiments in linear magnetized plasmas, Nucl. Fusion, 54, 114010-1-114010-5, 2014.11.
93. M. Lesur, P.H. Diamond, and Y. Kosuga, Phase-space jets drive transport and anomalous resistivity, Phys. Plasmas, 21, 112307-1-112307-9, 2014.11.
94. Z. Guo, P.H. Diamond, Y. Kosuga, O.D. Gurcan, Turbulence elasticity-A new mechanism for transport barrier dynamics, Phys. Plasmas, 21, 090702-1-090702-5, 2014.09.
95. Y. Kosuga, S.-I. Itoh, P.H. Diamond, K. Itoh, and M. Lesur, Ion temperature gradient driven Turbulence with strong trapped ion resonance, Phys. Plasmas, 21, 102303-1-102303-10, 2014.09.
96. H. Jhang, P.H. Diamond, M. Leconte, K. Ida, J.M. Kwon, N. Tamura, and Y. Kosuga, The 3rd Asia-Pacific Transport Working Group(APTWG) Meeting, Nucl. Fusion, 54, 047001-1-047001-8, 2014.04.
97. M. Lesur, P. H. Diamond, Y. Kosuga, Nonlinear current-driven ion-acoustic instability driven by phase-space structures, Plasma Phys. Control. Fusion, 56, 075005-1-075005-13, 2014.04.
98. Z.B. Guo, P. H. Diamond, Y. Kosuga, O. D. Gurcan, Elasticity in drift-wave–zonal-flow turbulence, Phys. Rev. E, 89, 041101(R)-1-041101(R)-5, 2014.04.
99. Y. Kosuga, P. H. Diamond, G. Dif-Pradalier, O. D. Gurcan, ExB shear pattern formation by radial propagation of heat flux waves, Phys. Plasmas, 21, 055701-1-055701-7, 2014.04.
100. H. Jhang, P.H. Diamond, M. Leconte, K. Ida, J.M. Kwon, N. Tamura, and Y. Kosuga, The 3rd Asia-Pacific Transport Working Group(APTWG) Meeting, Nucl. Fusion, 54, 047001-1-047001-8, 2014.04.
101. Inagaki Shigeru, Yudai Miwa, Tatsuya Kobayashi, Takuma Yamada, Yoshihiko Nagashima, Tomohiro Mitsuzono, Hiromitsu Fujino, Makoto Sasaki, Naohiro Kasuya, Maxime Lesur, Y. Kosuga, Akihide Fujisawa, SANAE INOUE(論文のみ) ITOH, Kimitaka Itoh, Identification of Quasi-Periodic Nonlinear Waveforms in Turbulent Plasmas, Plasma Fusion Res., 9, 1201016-1-1201016-2, 2014.03.
102. Kosuga Yusuke, SANAE INOUE(論文のみ) ITOH, Kimitaka Itoh, Immediate Influence of External Sources on Turbulent Plasma Transport, JPS Conf. Proc., 1, 015002-1-015002-5, 2014.03.
103. 小菅 佑輔, 伊藤 早苗, P. H. Diamond, 伊藤公孝, Maxime Lesur, Relative Dispersion of Trapped Ion Granulations in Sheared Flows, Plasma Fusion Res., 9, 3403018-1-3403018-4, 2014.03.
104. 小菅 佑輔, 伊藤 早苗, P. H. Diamond, 伊藤公孝, Conversion of poloidal flows into toroidal flows by phase space structures in trapped ion resonance driven turbulence, Plasma Phys. Control. Fusion, 55, 125001-1-125001-7, 2013.10, 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..
105. P.H. Diamond, 小菅 佑輔, O.D. Gurcan, C.J. McDevitt, T.S. Hahm, N. Fedorczak, J.E. Rice, W.X. Wang, S. Ku, J.M. Kwon, G. Dif-Pradalier, J. Abiteboul, L. Wang, W.H. Ko, Y.J. Shi, K. Ida, W. Solomon, H. Jhang, S.S. Kim, S. Yi, An overview of intrinsic torque and momentum transport bifurcations in toroidal plasmas, Nucl. Fusion, 53, 104019-1-104019-21, 2013.09.
106. K. Miki, P.H. Diamond, N. Fedorczak, O.D. Gurcan, M. Malkov, C. Lee, Yusuke Kosuga, G. Tynan, G.S. Xu, T. Estrada, D. McDonald, L. Schmitz, K.J. Zhao, Spatio-temporal evolution of the L-H and H-L transitions, Nucl. Fusion, 53, 073044-1-073044-10, 2013.06.
107. Yusuke Kosuga, P.H. Diamond, Blob-Hole Structures as Non-Axisymmetric Equilibrium Solutions for Potential Vorticity Conserving Fluids, Plasma Fusion Res., 8, 2403080-1-2403080-4, 2013.06.
108. Y. Kosuga, P.H. Diamond, L. Wang, O.D. Gurcan, T.S. Hahm, Progress on theoretical issues in modelling turbuelnt transport, Nucl. Fusion, 53, 043008, 2013.03.
109. Y. Kosuga, P.H. Diamond, and O.D. Gurcan, How the Propagation of Heat-Flux Modulations Triggers ExB Flow Pattern Formation, Phys. Rev. Lett., 110, 105002, 2013.03.
110. O.D. Gurcan, P.H. Diamond, X. Garbet, V. Berionni, G. Dif-Pradalier, P. Hennequin, P. Morel, Y. Kosuga, and L. Vermare, Transport of radial heat flux and second sound in fusion plasmas, Phys. Plasmas, 20, 022307, 2013.02.
111. Kosuga Yusuke, P.H. Diamond, Drift hole structrue and dynamics with turbulence driven flows, Phys. Plasmas, 19, 072307, 2012.07.
112. Kosuga Yusuke, P.H. Diamond, On relaxation and transport in gyrokinetic drift wave turbulence with zonal flow, Phys. Plasmas, 18, 122305-1-122305-16, 2011.12.
113. J.E. Rice, J.W. Hughes, P.H. Diamond, Kosuga Yusuke, Y.A. Podpaly, M.L. Reinke, M.J. Greenwald, O.D. Gurcan, T.S. Hahm, A.E. Hubbard, E.S. Marmar, C.J. McDevitt, D.G. Whyte, Edge Temperature Gradient as Intrinsic Rotation Drive in Alcator C-Mod Tokamak Plasmas, Phys. Rev. Lett., 106, 215001-1-215001-4, 2011.05.
114. Yusuke KOSUGA and Patrick H. DIAMOND, Collisionless Dynamical Friction and Relaxation in a Simple Drift Wave-Zonal Flow Turbulence, Plasma Fusion Res., 5, S2051, 2010.12.
115. Y. Kosuga, P.H. Diamond, and O.D. Gurcan, On the efficiency of intrinsic rotation generation in tokamaks, Phys. Plasmas, 17, 102313, 2010.10.