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篠原 孝司; 林 伸彦; 諫山 明彦; 宮戸 直亮; 浦野 創; 相羽 信行

プラズマ・核融合学会誌, 91(12), p.797 - 800, 2015/12



Integrated modelling of toroidal rotation with the 3D non-local drift-kinetic code and boundary models for JT-60U analyses and predictive simulations

本多 充; 佐竹 真介*; 鈴木 康浩*; 吉田 麻衣子; 林 伸彦; 神谷 健作; 松山 顕之; 篠原 孝司; 松永 剛; 仲田 資季; et al.

Nuclear Fusion, 55(7), p.073033_1 - 073033_11, 2015/07

 被引用回数:5 パーセンタイル:65.51(Physics, Fluids & Plasmas)

The integrated simulation framework for toroidal momentum transport is developed, which self-consistently calculates the neoclassical toroidal viscosity (NTV), the radial electric field $$E_r$$ and the resultant toroidal rotation $$V_phi$$ together with the scrape-off-layer(SOL)-physics based boundary model. The coupling of three codes, the 1.5D transport code, TOPICS, the 3D equilibrium code, VMEC and the 3D $$delta f$$ drift-kinetic equation solver, FORTEC-3D, makes it possible to calculate the NTV due to the non-axisymmetric perturbed magnetic field caused by toroidal field coils. Analyses reveal that the NTV significantly influences $$V_phi$$ in JT-60U and $$E_r$$ holds the key to determine the NTV profile. The sensitivity of the $$V_phi$$ profile to the boundary rotation necessitates a boundary condition modelling for toroidal momentum. Owing to the high-resolution measurement system in JT-60U, the $$E_r$$ gradient is found to be virtually zero at the separatrix regardless of toroidal rotation velocities. Focusing on $$E_r$$, the boundary model of toroidal momentum is developed in conjunction with the SOL/divertor plasma code D5PM. This modelling realizes self-consistent predictive simulations for operation scenario development in ITER.



篠原 孝司; 諫山 明彦; 鈴木 隆博; 吉田 麻衣子

プラズマ・核融合学会誌, 91(7), p.494 - 496, 2015/07


2015年の春季に国際トカマク物理活動(ITPA)に関する全4グループの会合が各グループ独立に開催された。「高エネルギー粒子物理」はフランスのITER機構で開催し日本からは2名の参加があった。「MHD安定性」はフランスのITER機構で開催し日本からは1名の参加があった。「統合運転シナリオ」はスペインのFusion for Energyで開催し日本からは3名の参加があった。「輸送と閉じ込め物理」はフランスのITER機構で開催し日本からは2名(TV会議参加)の参加があった。それぞれ、各極の関係者と国際装置間比較実験、ITERの物理に関する今後の課題、及び、各グループの活動計画の議論が行われた。これらの会合の概要をまとめて報告する。なお、次回会合は2015年の秋季に各グループ独立に開催する予定である。


Effects of the radial electric field on the confinement of fast ions in ITER

谷 啓二*; 本多 充; 及川 聡洋*; 篠原 孝司; 草間 義紀; 杉江 達夫

Nuclear Fusion, 55(5), p.053010_1 - 053010_15, 2015/05


 被引用回数:1 パーセンタイル:93.32(Physics, Fluids & Plasmas)



Alfv$'{e}$n acoustic channel for ion energy in high-beta tokamak plasmas

Bierwage, A.; 相羽 信行; 篠原 孝司

Physical Review Letters, 114(1), p.015002_1 - 015002_5, 2015/01

 被引用回数:7 パーセンタイル:41.67(Physics, Multidisciplinary)

When the plasma beta (ratio of thermal to magnetic pressure) in the core of a tokamak is raised to values of several percent, as required for a thermonuclear fusion reactor, continuous spectra of long-wavelength slow magnetosonic waves enter the frequency band occupied by continuous spectra of shear Alfv$'{e}$n waves. It is found that these two branches can couple strongly, so that Alfv$'{e}$n modes that are resonantly driven by suprathermal ions transfer some of their energy to sound waves. Since sound waves are heavily damped by thermal ion Landau resonances, these results reveal a new energy channel that contributes to the damping of Alfv$'{e}$nic instabilities and the noncollisional heating of bulk ions, with potentially important consequences for confinement and fusion performance.


Alfv$'{e}$n acoustic channel for ion energy in high-beta tokamak plasmas revisited with a linear gyrokinetic model (LIGKA)

Bierwage, A.; Lauber, P.*; 相羽 信行; 篠原 孝司; 矢木 雅敏

Proceedings of 14th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems (Internet), 8 Pages, 2015/00

A recently proposed Alfv$'{e}$n acoustic self-heating channel for burning plasmas - where fast-ion-driven shear Alfv$'{e}$n waves transfer energy to sound waves which then heat the bulk ions - is reexamined using a linear gyrokinetic model. A local eigenvalue analysis shows that the ion sound branches required for such a self-heating channel are so strongly damped that they are effectively non-existent when $$T_{rm e} approx 1.7times T_{rm i}$$. However, when $$T_{rm e}$$ is increased by a factor 2.8, low-frequency sound continua in the range of beta-induced Alfv$'{e}$n acoustic eigenmodes (BAAE) are recovered and their excitation becomes feasible. This raises the question whether higher-frequency sound branches in the frequency range of beta-induced Alfv$'{e}$n continuum modes (BACM) and the associated self-heating channels may exist under reactor-relevant conditions. Moreover, it is shown that modifications of the continuous spectra by fast ions may need to be taken into account.



諫山 明彦; 浦野 創; 宮戸 直亮; 井手 俊介; 朝倉 伸幸; 篠原 孝司

プラズマ・核融合学会誌, 90(12), p.830 - 833, 2014/12



Experimental analyses and predictive simulations of toroidal rotation driven by the neoclassical toroidal viscosity in rippled tokamaks

本多 充; 佐竹 真介*; 鈴木 康浩*; 松永 剛; 篠原 孝司; 吉田 麻衣子; 松山 顕之; 井手 俊介; 浦野 創

Nuclear Fusion, 54(11), p.114005_1 - 114005_14, 2014/11

 被引用回数:10 パーセンタイル:43.27(Physics, Fluids & Plasmas)

A cooperation framework for analyses and predictions of the neoclassical toroidal viscosity (NTV) and the resultant toroidal flow is developed among the TOPICS, VMEC and FORTEC-3D codes. With the real geometry in JT-60U taken into account, it is found that the NTV is one of the cardinal torque sources especially in the edge region irrespective of the insertion of the ferritic steel tiles (FSTs) that reduce the toroidal field ripple amplitude and it is essential to numerically reproduce the measured toroidal rotation profile in the edge. The up-down asymmetric component of the NTV is damped due to the FSTs and the NTV profile correlates with the profile of the radial electric field $$E_r$$. Predictive simulations for JT-60SA H-mode scenarios are also performed to investigate the effects of the NTV on toroidal rotation. The NTV reversal is observed in the pedestal region where the steep pressure gradient is formed, due to the dependence of the NTV on $$E_r$$.


Orbit-based analysis of resonant excitations of Alfv$'e$n waves in tokamaks

Bierwage, A.; 篠原 孝司

Physics of Plasmas, 21(11), p.112116_1 - 112116_21, 2014/11

 被引用回数:15 パーセンタイル:31(Physics, Fluids & Plasmas)

The resonant interactions between shear Alfv$'e$n waves and resonant fast ions are analyzed numerically in realistic geometry and with a realistic particle distribution for a JT-60U plasma driven by two 400 keV N-NBs. In order to deal with the large magnetic drifts of the fast ions, a new orbit-based resonance analysis (ORA) method is developed and applied. The ORA method uses mappings that allows us to unify resonance conditions for trapped and passing particles, determine which harmonics are driven, and which orders of the resonance are involved. After analyzing the resonance conditions, the effects of wave-particle trapping, kinetic compression and linear resonance overlap are examined. Finally, we discuss the implications for frequency chirping, convective amplification, the long-time evolution of the system in the presence of a fast ion source, and for the interpretation of experimental observations.


Evaluation of two-stage system for neutron measurement aiming at increase in count rate at Japan Atomic Energy Agency - Fusion Neutronics Source

篠原 孝司; 石井 啓一*; 落合 謙太郎; 馬場 護*; 助川 篤彦; 笹尾 眞實子*; 北島 純男*

Review of Scientific Instruments, 85(11), p.11E823_1 - 11E823_4, 2014/11

 被引用回数:0 パーセンタイル:100(Instruments & Instrumentation)

A neutron flux array is one of the important plasma diagnostics to obtain the information on fast ion population. However, the limited flux owing to its collimator results in the small number of pulse counts and the large statistical error. The method to increase the pulse counts is required. Here, we propose a multi-stage neutron detection system, in which several sets of a scintillator and photo-multiplier tube (PMT) are placed in a line-of-sight. In order to evaluate the performance of the multi-stage detection system, we have carried out experiments on a two-stage detection system using a neutron beam at FNS (Fusion Neutronics Source) of JAEA (Japan Atomic Energy Agency). The results have shown the concept of the multi-stage detection system works as expected. In the best setup, the test two-stage system reached about 1.7 (1.8) times the efficiency of a single scintillator and PMT system for 2.54 (14) MeV neutrons.


A Study on fast digital discrimination of neutron and $$gamma$$-ray for improvement neutron emission profile measurement

内田 雄大*; 高田 英治*; 藤崎 明広*; 磯部 光孝*; 小川 国大*; 篠原 孝司; 富田 英生*; 河原林 順*; 井口 哲夫*

Review of Scientific Instruments, 85(11), p.11E118_1 - 11E118_4, 2014/11

 被引用回数:4 パーセンタイル:73.17(Instruments & Instrumentation)

Neutron and $$gamma$$-ray discrimination with a digital signal processing system has been used to measure the neutron emission profile in magnetic confinement fusion devices. However, a sampling rate must be set low to extend the measurement time because the memory storage is limited. Time jitter decreases a discrimination quality due to a low sampling rate. As described in this paper, a new charge comparison method was developed. Furthermore, automatic neutron-$$gamma$$ discrimination method was examined using a probabilistic approach. Analysis results were investigated using the figure of merit. Results show that the discrimination quality was improved. Automatic discrimination was applied using the EM algorithm and k-means algorithm.


Dynamics of low-$$n$$ shear Alfv$'e$n modes driven by energetic N-NB ions in JT-60U

Bierwage, A.; 藤堂 泰*; 相羽 信行; 篠原 孝司

Nuclear Fusion, 54(10), p.104001_1 - 104001_14, 2014/10

 被引用回数:14 パーセンタイル:33.73(Physics, Fluids & Plasmas)

Dynamics of fast ions and shear Alfv$'e$n waves are simulated using MEGA, a global nonlinear hybrid code. The scenario is based on JT-60U shot E039672, driven by strong negative-ion-based neutral beams (N-NB), just before the onset of a so-called Abrupt Large Event (ALE). It is found that modes with toroidal mode numbers $$n$$ = 2, 3, 4 can be destabilized, besides the $$n$$ = 1 mode studied previously. The properties of the modes with n $$>$$ 1 are sensitive to the value of the plasma beta and the form of the fast ion distribution, so simulation conditions are set up as realistically as possible. When the fast ion drive exceeds a certain threshold, the $$n$$ = 3 mode is enhanced through a convective amplification process while following fast ions that were displaced by the field fluctuations. The fast ion transport in several cases is analyzed and implications of the results for the explanation of ALEs are discussed.


Integrated modeling of toroidal rotation with the 3D non-local drift-kinetic code and boundary models for JT-60U analyses and predictive simulations

本多 充; 佐竹 真介*; 鈴木 康浩*; 吉田 麻衣子; 林 伸彦; 神谷 健作; 松山 顕之; 篠原 孝司; 松永 剛; 仲田 資季; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

The integrated framework for toroidal momentum transport is developed, which self-consistently calculates the neoclassical toroidal viscosity (NTV), the radial electric field $$E_r$$ and resultant toroidal rotation together with the scrape-off-layer (SOL) physics-based boundary model. The coupling of three codes, TOPICS, VMEC and FORTEC-3D, can calculate rotation caused by the NTV due to the non-axisymmetric perturbed magnetic field caused by toroidal field coils. It is found that the NTV influences toroidal rotation in JT-60U and $$E_r$$ holds the key to determine the NTV profile. The sensitivity of the toroidal rotation profile to the boundary rotation necessitates the boundary condition modeling. From the measurement in JT-60U, the $$E_r$$ gradient is found to be insensitive at the separatrix. Focusing on $$E_r$$, the boundary model of toroidal momentum is developed in conjunction with the SOL/divertor plasma code. This modeling realizes self-consistent predictive simulations for operation scenario development in ITER.


Multi-time-scale energetic particle dynamics in JT-60U simulated with MHD activity, sources and collisions

Bierwage, A.; 篠原 孝司; 藤堂 泰*; 矢木 雅敏

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

The global nonlinear hybrid code MEGA was extended with a fast ion source and a collision model, so that the formation of the fast ion slowing-down distribution (long time scale, 1ms-1s) and the interaction between the fast ions and MHD waves (short time scale, 0.001-1ms) can be simulated simultaneously. This self-consistent approach, without artificial interfaces, allows to simulate meso-time-scale dynamics (0.1-10ms), such as recurring bursts of MHD activity and the resulting relaxations of the fast ion distribution. When applied to a JT-60U plasma driven by 400 keV negative-ion-based neutral beams (N-NB), the code successfully reproduced experimentally observed bursts of chirping modes. Thus validated, the new multi-time-scale simulations allows for the first time to study the physics of burstiness and frequency chirping in a realistic setting, and first results are presented and discussed. The advances made constitute an important step towards predictive simulations.



林 伸彦; 相羽 信行; 諫山 明彦; 篠原 孝司; 本多 充

プラズマ・核融合学会誌, 90(6), p.352 - 355, 2014/06



Dynamics of energetic particle driven modes and MHD modes in wall-stabilized high-$$beta$$ plasmas on JT-60U and DIII-D

松永 剛; 岡林 典男*; 相羽 信行; Boedo, J. A.*; Ferron, J. R.*; Hanson, J. M.*; Hao, G. Z.*; Heidbrink, W. W.*; Holcomb, C. T.*; In, Y.*; et al.

Nuclear Fusion, 53(12), p.123022_1 - 123022_13, 2013/12

 被引用回数:2 パーセンタイル:88.58(Physics, Fluids & Plasmas)

In the wall-stabilized high-$$beta$$ plasmas in JT-60U and DIII-D, interactions between energetic particle (EP) driven modes (EPdMs) and edge localized modes (ELMs) have been observed. The interaction between the EPdM and ELM are reproducibly observed. Many EP diagnostics indicate that strong correlation between the distorted waveform of the EPdM and the EP transport to edge. The waveform distortion is composed of higher harmonics $$(n ge 2)$$ and it looks like a density snake near the plasma edge. According to statistical analyses, the ELM triggering by the EPdMs needs finite level of waveform distortion and pedestal recovery. The ELM pacing by the EPdMs occurs when the repetition frequency of the EPdMs is higher than the natural ELM frequency. Transported EPs by the EPdMs are thought to contribute to change the edge stability.



吉田 麻衣子; 篠原 孝司; 林 伸彦; 諫山 明彦; 神谷 健作

プラズマ・核融合学会誌, 89(12), p.887 - 889, 2013/12



Research and development of neutron detection system using scintillator and digital-signal processing

篠原 孝司; 石井 啓一*; 落合 謙太郎; 馬場 護*; 笹尾 眞實子*; 北島 純男*

Plasma and Fusion Research (Internet), 8, p.1402144_1 - 1402144_9, 2013/11

A collimated neutron flux array system in JT-60U successfully upgraded performance of higher counting rate and the capability to detect 14 MeV neutrons as well by using a fast digitizer in 2006. Additionally, detailed analysis of the recorded waveform on JT-60U and FNS has provided us new findings. In this paper, firstly, characteristics of pulse shapes and neutron-$$gamma$$ discrimination parameters investigated by the detailed analysis of digitized waveform data are described. Next, new data analysis procedure for neutron-$$gamma$$ discrimination based on the characteristics is proposed. In the new procedure, an appropriate projection surface, on which we can define the discrimination boundary, has been introduced in three-dimensional discrimination parameter space. The problem of pulse height variation, which occurs when a counting rate is high in high performance plasma, and its countermeasures are also presented. The system using the countermeasure of a booster method successfully has avoided the problem in the high neutron flux condition of $$sim$$2$$times$$10$$^{5}$$ counts/s on FNS.


Role of convective amplification of $$n$$=1 energetic particle modes for N-NB ion dynamics in JT-60U

Bierwage, A.; 篠原 孝司; 相羽 信行; 藤堂 泰*

Nuclear Fusion, 53(7), p.073007_1 - 073007_12, 2013/07

 被引用回数:14 パーセンタイル:39.32(Physics, Fluids & Plasmas)

The hybrid code MEGA is used to simulate an Abrupt Large-amplitude Event (ALE) in JT-60U. The goal is to look for a threshold with respect to the fast ion beta beyond which Energetic Particle Modes (EPM) undergo convective amplification and cause significant fast ion transport. This is motivated by the hypothesis that such a threshold may work as a trigger mechanism for relaxation events, such as ALE. In order to facilitate quantitative comparisons with the experiment, a realistic geometry, bulk pressure and fast ion distribution are used. Consistently with the experiment, the simulation predicts a burst time of about 0.3 ms and peak magnetic fluctuation levels $$delta$$$$beta$$$$_{vartheta}$$/$$beta$$$$<$$10$$^{-3}$$ at the plasma boundary. As $$beta$$$$_{h0}$$ is increased, a gradual (not sharp) increase in the convective amplification of the EPM and in the convective transport is found. It is concluded that the onset of convective amplification does not suffice as a trigger mechanism for ALE.


ELM triggering by energetic particle driven mode in wall-stabilized high-$$beta$$ plasmas

松永 剛; 相羽 信行; 篠原 孝司; 朝倉 伸幸; 諫山 明彦; 大山 直幸; JT-60チーム

Nuclear Fusion, 53(7), p.073046_1 - 073046_9, 2013/06

 被引用回数:2 パーセンタイル:88.58(Physics, Fluids & Plasmas)

In the JT-60U high-$$beta$$ plasmas above the no-wall $$beta$$ limit, a triggering of an edge localized mode (ELM) by an energetic particle (EP) driven mode has been observed. This EP-driven mode is thought to be driven by trapped EPs and it has been named EP driven wall mode (EWM) on JT-60U. When the EWM appears in an ELMy H-mode phase, ELM crashes are reproducibly synchronized with the EWM bursts. The EP-driven mode has a higher repetition frequency and less energy loss than those of the natural ELM. In order to trigger an ELM by the EP-driven mode, some conditions are thought to be needed, thus an EWM with large amplitude and growth rate, and marginal edge stability. In the scrape off layer region, several measurements indicate an ion loss induced by the Emote ion loss considered as the EP loss through the edge region can increase a local pressure gradient at the pedestal region, and then affect the edge stability.

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