Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks

Wang, Feng; Fu, G. Y.; Breslau, J.; Liu, J. Y.

doi:10.1063/1.4824739

Cited by 45 publications

(56 citation statements)

References 14 publications

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“…The M3D-K code has been extensively applied to study MHD modes and energetic particle instabilities in tokamaks. 12,13,[29][30][31][32][33][34] We consider a beam-heated discharge in DIII-D plasmas. As shown in Fig.…”

Section: M3d-k Model and Basic Parametersmentioning

confidence: 99%

“…11 Wang et al then further investigated the linear and nonlinear dynamics of the NRK in NSTX considering toroidal rotation 12 and energetic particle effects. 13 Also in the RFX-mode reversed field pinch the SHAx state was reported. 14 The snakes, LLMs, SHAx, etc., as suggested by Cooper et al, [15][16][17] represent the same physical phenomenon: saturated dominantly m ¼ 1; n ¼ 1 internal kink modes.…”

Section: Introductionmentioning

confidence: 95%

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Nonlinear hybrid simulation of internal kink with beam ion effects in DIII-D

Shen

Tobias

et al. 2015

Physics of Plasmas

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In DIII-D sawteething plasmas, long-lived (1,1) kink modes are often observed between sawtooth crashes. The saturated kink modes have two distinct frequencies. The mode with higher frequency transits to a fishbone-like mode with sufficient on-axis neutral beam power. In this work, hybrid simulations with the global kinetic-magnetohydrodynamic (MHD) hybrid code M3D-K have been carried out to investigate the linear stability and nonlinear dynamics of the n ¼ 1 mode with effects of energetic beam ions for a typical DIII-D discharge where both saturated kink mode and fishbone were observed. Linear simulation results show that the n ¼ 1 internal kink mode is unstable in MHD limit. However, with kinetic effects of beam ions, a fishbone-like mode is excited with mode frequency about a few kHz depending on beam pressure profile. The mode frequency is higher at higher beam power and/or narrower radial profile consistent with the experimental observation. Nonlinear simulations have been performed to investigate mode saturation as well as energetic particle transport. The nonlinear MHD simulations show that the unstable kink mode becomes a saturated kink mode after a sawtooth crash. With beam ion effects, the fishbone-like mode can also transit to a saturated kink mode with a small but finite mode frequency. These results are consistent with the experimental observation of saturated kink mode between sawtooth crashes. V C 2015 AIP Publishing LLC. [http://dx.

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Section: M3d-k Model and Basic Parametersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Nonlinear hybrid simulation of internal kink with beam ion effects in DIII-D

Shen

Tobias

et al. 2015

Physics of Plasmas

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“…It computes the initial value solutions of the kinetic/MHD equations in toroidal geometry. The M3D-K code has been used successfully in simulating TAEs in a tokamak equilibrium with circular flux surfaces, 19 tearing modes in a low beta tokamak plasma, 20 kink modes and fishbones in ITER and NSTX, 12,21,22 and fast-ion-driven Reversed Shear Alfv en Eigenmodes (RSAE) in the DIII-D Tokamak. 23 In the present work, we mainly focus on the linear simulations of fast ion driven TAEs on NSTX for the purpose of code validation.…”

Section: Introductionmentioning

confidence: 99%

Hybrid simulation of toroidal Alfvén eigenmode on the National Spherical Torus Experiment

Liu

Crocker³

et al. 2015

Physics of Plasmas

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Energetic particle modes and Alfv en eigenmodes driven by super-Alfv enic fast ions are routinely observed in neutral beam heated plasmas on the National Spherical Torus eXperiment (NSTX). These modes can significantly impact fast ion transport and thus cause fast ion redistribution or loss. Self-consistent linear simulations of Toroidal Alfv en Eigenmodes (TAEs) in NSTX plasmas have been carried out with the kinetic/magnetohydrodynamic hybrid code M3D-K using experimental plasma parameters and profiles including plasma toroidal rotation. The simulations show that unstable TAEs with n ¼ 3; 4; or 5 can be excited by the fast ions from neutral beam injection. The simulated mode frequency, mode radial structure, and phase shift are consistent with measurements from a multi-channel microwave reflectometer diagnostic. A sensitivity study on plasma toroidal rotation, safety factor q profile, and initial fast ion distribution is performed. The simulations show that rotation can have a significant destabilizing effect when the rotation is comparable or larger than the experimental level. The mode growth rate is sensitive to q profile and fast ion distribution. Although mode structure and peak position depend somewhat on q profile and plasma rotation, the variation of synthetic reflectometer response is within experimental uncertainty and it is not sensitive enough to see the difference clearly. V C 2015 AIP Publishing LLC.

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“…NSTX discharges have exhibited the co-existence of the NRK with higher frequency, beam-driven fishbone modes (EPMs), and linear and non-linear simulations using the global kinetic/MHD hybrid M3D-K code [25] were carried out to study the energetic particle interaction with the NRK [26]. Figure 10 shows the map of mode stability as a function of q min and β hot /β total at a fixed input power.…”

Section: Non-inductive Sustainment: Energetic Particle Physics and Nementioning

confidence: 99%

An overview of recent physics results from NSTX

Kaye¹,

Abrams²,

Ahn³

et al. 2015

Nucl. Fusion

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The National Spherical Torus Experiment (NSTX) is currently being upgraded to operate at twice the toroidal field and plasma current (up to 1 T and 2 MA), with a second, more tangentially aimed neutral beam (NB) for current and rotation control, allowing for pulse lengths up to 5 s. Recent NSTX physics analyses have addressed topics that will allow NSTX-Upgrade to achieve the research goals critical to a Fusion Nuclear Science Facility. These include producing stable, 100% non-inductive operation in high-performance plasmas, assessing plasma-material interface (PMI) solutions to handle the high heat loads expected in the next-step devices and exploring the unique spherical torus (ST) parameter regimes to advance predictive capability. Non-inductive operation and current profile control in NSTX-U will be facilitated by co-axial helicity injection (CHI) as well as radio frequency (RF) and NB heating. CHI studies using NIMROD indicate that the reconnection process is consistent with the 2D Sweet-Parker theory. Full-wave AORSA simulations show that RF power losses in the scrape-off layer (SOL) increase significantly for both NSTX and NSTX-U when the launched waves propagate in the SOL. Toroidal Alfvén eigenmode avalanches and higher frequency Alfvén eigenmodes can affect NB-driven current through energy loss and redistribution of fast ions. The inclusion of rotation and kinetic resonances, which depend on collisionality, is necessary for predicting experimental stability thresholds of fast growing ideal wall and resistive wall modes. Neutral beams and neoclassical toroidal viscosity generated from applied 3D fields can be used as actuators to produce rotation profiles optimized for global stability. DEGAS-2 has been used to study the dependence of gas penetration on SOL temperatures and densities for the MGI system being implemented on the Upgrade for disruption mitigation. PMI studies have focused on the effect of ELMs and 3D fields on plasma detachment and heat flux handling. Simulations indicate that snowflake and impurity seeded radiative divertors are candidates for heat flux mitigation in NSTX-U. Studies of lithium evaporation on graphite surfaces indicate that lithium increases oxygen surface concentrations on graphite, and deuterium-oxygen affinity, which increases deuterium pumping and reduces recycling. In situ and test-stand experiments of lithiated graphite and molybdenum indicate temperature-enhanced sputtering, although that test-stand studies also show the potential for heat flux reduction through lithium vapour shielding. Non-linear gyro kinetic simulations have indicated that ion transport can be enhanced by a shear-flow instability, and that non-local effects are necessary to explain the observed rapid changes in plasma turbulence. Predictive simulations have shown agreement between a microtearing-based reduced transport model and the measured electron temperatures in a microtearing unstable regime. Two Alfvén eigenmode-driven fast ion transport models have been developed and successfully b...

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Linear stability and nonlinear dynamics of the fishbone mode in spherical tokamaks

Cited by 45 publications

References 14 publications

Nonlinear hybrid simulation of internal kink with beam ion effects in DIII-D

Nonlinear hybrid simulation of internal kink with beam ion effects in DIII-D

Hybrid simulation of toroidal Alfvén eigenmode on the National Spherical Torus Experiment

An overview of recent physics results from NSTX

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