九州大学 研究者情報
論文一覧
小菅 佑輔(こすが ゆうすけ) データ更新日:2018.05.28

准教授 /  応用力学研究所 核融合力学部門


原著論文
1. Yusuke Kosuga, How pattern is selected in drift wave turbulence
Role of parallel flow shear, Physics of Plasmas, 24, 12, https://doi.org/10.1063/1.5001857, 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..
2. 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.
3. 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.
4. Y. Kosuga, S.-I. Itoh and K. Itoh, Zonal flow generation in parallel flow shear driven turbulence, Phys. Plasmas, 24, 032304, 2017.01.
5. 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, 57, 7, https://doi.org/10.1088/1741-4326/aa665a, 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..
6. , 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, 57, 7, https://doi.org/10.1088/1741-4326/aa6f35, 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..
7. 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, 57, 11, https://doi.org/10.1088/1741-4326/aa7b44, 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..
8. 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, 57, 10, https://doi.org/10.1088/1741-4326/aa796a, 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..
9. 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, 57, 12, https://doi.org/10.1088/1741-4326/aa8341, 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..
10. 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, 24, 11, https://doi.org/10.1063/1.5000343, 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..
11. 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, 7, 1, https://doi.org/10.1038/s41598-017-17011-y, 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..
12. 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, 87, 3, https://doi.org/10.7566/JPSJ.87.034501, 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..
13. 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, 25, 1, https://doi.org/10.1063/1.5008541, 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..
14. 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, 3401024-7, 2015.04.
15. 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, 2015.04.
16. 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, 043022-4, 2015.03.
17. 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, 085004-5, 2015.02.
18. 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, 1203002-2, 2015.01.
19. 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, 013022-19, 2015.01.
20. 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, 017001-10, 2014.12.
21. M. Lesur, P.H. Diamond, and Y. Kosuga, Phase-space jets drive transport and anomalous resistivity, Phys. Plasmas, 21, 112307-9, 2014.11.
22. 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, 114010-5, 2014.11.
23. 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, 102303-10, 2014.09.
24. Z. Guo, P.H. Diamond, Y. Kosuga, O.D. Gurcan, Turbulence elasticity-A new mechanism for transport barrier dynamics, Phys. Plasmas, 21, 090702-5, 2014.09.
25. 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, 047001-8, 2014.04.
26. 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, 055701-7, 2014.04.
27. Z.B. Guo, P. H. Diamond, Y. Kosuga, O. D. Gurcan, Elasticity in drift-wave–zonal-flow turbulence, Phys. Rev. E, 89, 041101(R)-5, 2014.04.
28. M. Lesur, P. H. Diamond, Y. Kosuga, Nonlinear current-driven ion-acoustic instability driven by phase-space structures, Plasma Phys. Control. Fusion, 56, 075005-13, 2014.04.
29. 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, 047001-8, 2014.04.
30. 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, 3403018-4, 2014.03.
31. Kosuga Yusuke, SANAE INOUE(論文のみ) ITOH, Kimitaka Itoh, Immediate Influence of External Sources on Turbulent Plasma Transport, JPS Conf. Proc., 1, 015002-5, 2014.03.
32. 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, 1201016-2, 2014.03.
33. 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, 125001-7, 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..
34. 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, 104019-21, 2013.09.
35. Yusuke Kosuga, P.H. Diamond, Blob-Hole Structures as Non-Axisymmetric Equilibrium Solutions for Potential Vorticity Conserving Fluids, Plasma Fusion Res., 8, 2403080-4, 2013.06.
36. 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, 215001-4, 2011.05.
37. Kosuga Yusuke, P.H. Diamond, On relaxation and transport in gyrokinetic drift wave turbulence with zonal flow, Phys. Plasmas, 18, 122305-16, 2011.12.
38. Kosuga Yusuke, P.H. Diamond, Drift hole structrue and dynamics with turbulence driven flows, Phys. Plasmas, 19, 072307, 2012.07.
39. 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.
40. 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.
41. 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.
42. 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, 073044-10, 2013.06.
43. 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.
44. Y. Kosuga, P.H. Diamond, and O.D. Gurcan, On the efficiency of intrinsic rotation generation in tokamaks, Phys. Plasmas, 17, 102313, 2010.10.

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