Spontaneous hole–clump pair creation

Berk, H. L.; Breǐzman, B. N.; Candy, J.; Pekker, M.; Petviashvili, N. V.

doi:10.1063/1.873550

Cited by 142 publications

(203 citation statements)

References 19 publications

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“…However, in the theory proposed by Berk, Breizman, and Petviashvili [36][37][38] for the spontaneous generation of hole-clump pairs, albeit for a one-dimensional ͑1-D͒ bump-on-tail resonant interaction, would predict exactly this type of behavior. In this theory, the nonlinear interaction of a marginally unstable resonant mode with a collisionless, inverted fast-particle distribution results in the splitting of the mode frequency, and upward and downward frequency chirping as the "holes" and "clumps" formed in the distribution function propagate in particle phase space.…”

Section: Compressional and Global Alfvén Modesmentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

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A wide variety of fast ion driven instabilities are excited during neutral beam injection ͑NBI͒ in the National Spherical Torus Experiment ͑NSTX͒ ͓Nucl. Fusion 40, 557 ͑2000͔͒ due to the large ratio of fast ion velocity to Alfvén velocity, V fast / V Alfvén , and high fast ion beta. The ratio V fast / V Alfvén in ITER ͓Nucl. Fusion 39, 2137 ͑1999͔͒ and NSTX is comparable. The modes can be divided into three categories: chirping energetic particle modes ͑EPM͒ in the frequency range 0 to 120 kHz, the toroidal Alfvén eigenmodes ͑TAE͒ with a frequency range of 50 kHz to 200 kHz, and the compressional and global Alfvén eigenmodes ͑CAE and GAE, respectively͒ between 300 kHz and the ion cyclotron frequency. Fast ion driven modes are of particular interest because of their potential to cause substantial fast ion losses. In all regimes of NBI heated operation we see transient neutron rate drops, correlated with bursts of TAE or fishbone-like EPMs. The fast ion loss events are predominantly correlated with the EPMs, although losses are also seen with bursts of multiple, large amplitude TAE. The latter is of particular significance for ITER; the transport of fast ions from the expected resonance overlap in phase space of a "sea" of large amplitude TAE is the kind of physics expected in ITER. The internal structure and amplitude of the TAE and EPMs has been measured with quadrature reflectometry and soft x-ray cameras. The TAE bursts have internal amplitudes of ñ / n = 1% and toroidal mode numbers 2 Ͻ n Ͻ 7. The EPMs are core localized, kink-like modes similar to the fishbones in conventional aspect ratio tokamaks. Unlike the fishbones, the EPMs can be present with q͑0͒ Ͼ 1 and can have a toroidal mode number n Ͼ 1. The range of the frequency chirp can be quite large and the resonance can be through a fishbone-like precessional drift resonance, or through a bounce resonance.

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Section: Compressional and Global Alfvén Modesmentioning

confidence: 99%

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

et al. 2006

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“…In addition, chaotic solutions can display shifting of the mode frequency ͑chirping͒, both upwardly and downwardly, as pairs of hole and clump are formed in the distribution. [8][9][10] On the one hand, theories have been developed by Berk et al 6,[8][9][10][11] to predict the quantitative behavior of such instabilities in various parameter regimes and explain underlying mechanisms. The validity of some of these theories has been tested by numerical simulations based on a reduced model solving only resonant particles with adiabatic and cold bulk plasmas.…”

Section: Introductionmentioning

confidence: 99%

Fully nonlinear features of the energetic beam-driven instability

2009

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The so-called Berk-Breizman model is applied to a cold bulk, weak warm beam, one-dimensional plasma, to investigate the kinetic instability arising from the resonance of a single electrostatic wave with an energetic particle beam. A Vlasov code is developed to solve the initial value problem for the full-f distribution, and the nonlinear evolution is categorized in the whole parameter space as damped, steady-state, periodic, chaotic, or chirping. The saturation level of steady-state solutions and the bifurcation between steady-state and periodic solutions near marginal stability match analytic predictions. The limit of a perturbative numerical approach when the resonant region extends into the bulk is shown. Frequency sweeping is observed, with time-evolution approaching theoretical results. A new method to extract the dissipation rate from frequency diagnostics is proposed. For small collision rates, instabilities are observed in the linearly barely stable region.

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“…9 The ratio of the linear damping rate ␥ d to the linear growth rate ␥ L in the simulation is consistent with hole-clump pair creation which takes place when ␥ d / ␥ L is greater than 0.4. 10,11 In this paper, we focus on the linear properties of the unstable mode. In Ref.…”

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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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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Spontaneous hole–clump pair creation

Cited by 142 publications

References 19 publications

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Collective fast ion instability-induced losses in National Spherical Tokamak Experiment

Fully nonlinear features of the energetic beam-driven instability

Nonlocal energetic particle mode in a JT-60U plasma

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