Alfvén eigenmodes driven by Alfvénic beam ions in JT-60U

Shinohara, K.; Kusama, Y.; Takechi, M.; Morioka, A.; Ishikawa, Masatoshi; Oyama, N.; Tobita, K.; Ozeki, T.; Takeji, S.; Moriyama, S.; Fujita, T.; Oikawa, T.; Suzuki, Takashi; Nishitani, T.; Kondoh, T.; Lee, S.; Kuriyama, M.; Team, Jt; Kramer, G. J.; Gorelenkov, N. N.; Nazikian, R.; Cheng, C. Z.; Fu, G. Y.; Fukuyama, A.

doi:10.1088/0029-5515/41/5/313

Cited by 105 publications

(129 citation statements)

References 25 publications

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“…The JT-60U discharge E36379, 4 where the fast FS mode was observed, was investigated using the MEGA code. The safety factor profile, bulk pressure profile, and density profile used in the simulation are based on the experimental data.…”

Section: A Instability In a Jt-60u Plasmamentioning

confidence: 99%

“…1) plasmas heated with negative ion based neutral beam (NNB) injection. [2][3][4][5] Frequencies of the three instabilities are in the range of shear Alfvén eigenmodes. Frequency sweeping of slow FS mode has a good correlation with equilibrium parameter evolution with time scale Ӎ200 ms. On the other hand, time scales of the fast FS mode and the ALE are, respectively 1 -5 ms and 200-400 s, much shorter than the equilibrium time scale.…”

Section: Introductionmentioning

confidence: 99%

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Nonlocal energetic particle mode in a JT-60U plasma

Todo

Shinohara²,

Takechi³

et al. 2004

Physics of Plasmas

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Energetic-ion driven instability in a Japan Atomic Energy Research Institute Tokamak-60 Upgrade (JT-60U) [S. Ishida et al., Phys. Plasmas 11, 2532(2004] plasma was investigated using a simulation code for magnetohydrodynamics and energetic particles. The spatial profile of the unstable mode peaks near the plasma center where the safety factor profile is flat. The unstable mode is not a toroidal Alfvén eigenmode (TAE) because the spatial profile deviates from the expected location of TAE and the spatial profile consists of a single primary harmonic m / n =2/1 where m and n are poloidal and toroidal mode numbers. The real frequency of the unstable mode is close to the experimental starting frequency of the fast frequency sweeping mode. Simulation results demonstrate that energetic-ion orbit width and energetic-ion pressure significantly broaden radial profile of the unstable mode. For the smallest value among the investigated energetic-ion orbit width, the unstable mode is localized within 20% of the minor radius. This gives an upper limit of the spatial profile width of the unstable mode which the magnetohydrodynamic effects alone can induce. For the experimental condition of the JT-60U plasma, energetic ions broaden the radial width of the unstable mode spatial profile by a factor of 3. The unstable mode is primarily induced by the energetic particles.

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Section: A Instability In a Jt-60u Plasmamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Nonlocal energetic particle mode in a JT-60U plasma

Todo

Shinohara²,

Takechi³

et al. 2004

Physics of Plasmas

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“…Simulations are carried out for cases based on the neutral-beam-driven JT-60U discharge E039672, where so-called abrupt large events (ALE) are observed [4,5]. These modes have frequencies in the range 40 kHz f 60 kHz and toroidal mode number n = 1, and cause significant energetic ion transport [4].…”

Section: Introductionmentioning

confidence: 99%

Nonlinear Simulation of Energetic Particle Modes in High-Beta Tokamak Plasma

Bierwage

Aiba

Todo

et al. 2013

Plasma and Fusion Research

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The effect of bulk pressure on the nonlinear dynamics of energetic particle modes (EPM) in a neutral-beamdriven JT-60U discharge is examined through nonlinear hybrid (MHD + particle) simulations with realistic values of the plasma beta and in realistic flux surface geometry. In the scenario studied, the linear EPM growth rate is 20% higher in the finite-beta compared to the zero-beta case, but compressibility stabilizes the mode by roughly the same amount. In the finite-beta case, the nonlinear frequency shift and the radial spreading/propagation of the mode are affected by the beta-induced gap in the shear Alfvén continuum. Although the evolution of the modes is affected by bulk pressure, compressibility and geometry, the overall energetic ion transport during the first few 100 Alfvén times following the saturation of the EPM is comparable in all cases studied.

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“…In contrast, in the case of neutral beam injection ͑NBI͒, a "hard" nonlinear regime is observed more often, resulting in bursting amplitude evolution and in rapid frequency sweeping. [9][10][11][12][13] Spontaneous formation of phase space holes and clumps 14 is typical of the NBI-driven scenarios. 9 The holes and clumps in the energetic particle distribution function correspond to resonant particles that are trapped in the field of the wave.…”

Section: Introductionmentioning

confidence: 99%

Effect of dynamical friction on nonlinear energetic particle modes

Lilley¹,

Breǐzman²,

Sharapov³

2010

Physics of Plasmas

106

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A fully nonlinear model is developed for the bump-on-tail instability including the effects of dynamical friction ͑drag͒ and velocity space diffusion on the energetic particles driving the wave. The results show that drag provides a destabilizing effect on the nonlinear evolution of waves. Specifically, in the early nonlinear phase of the instability, the drag facilitates the explosive scenario of the wave evolution, leading to the creation of phase space holes and clumps that move away from the original eigenfrequency. Later in time, the electric field associated with a hole is found to be enhanced by the drag, whereas for a clump it is reduced. This leads to an asymmetry of the frequency evolution between holes and clumps. The combined effect of drag and diffusion produces a diverse range of nonlinear behaviors including hooked frequency chirping, undulating, and steady state regimes. An analytical model is presented, which explains the aforementioned diversity. A continuous production of hole-clump pairs in the absence of collisions is also observed.

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Alfvén eigenmodes driven by Alfvénic beam ions in JT-60U

Cited by 105 publications

References 25 publications

Nonlocal energetic particle mode in a JT-60U plasma

Nonlocal energetic particle mode in a JT-60U plasma

Nonlinear Simulation of Energetic Particle Modes in High-Beta Tokamak Plasma

Effect of dynamical friction on nonlinear energetic particle modes

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