Global gyrokinetic nonlinear simulations of kinetic infernal modes in reversed shear tokamaks
Global gyrokinetic nonlinear simulations of kinetic infernal modes in reversed shear tokamaks
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DOI：
10.1063/5.0013349
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发表时间：
2020-09
影响因子：
2.2
通讯作者：
Y. Ishida;A. Ishizawa;K. Imadera;Yasuaki Kishimoto;Yuji Nakamura
中科院分区：
文献类型：
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作者：
Y. Ishida;A. Ishizawa;K. Imadera;Yasuaki Kishimoto;Yuji Nakamura
本文用全局回旋动力学方法研究了反向剪切等离子体中电磁不稳定性的非线性演化。结果表明，动力学内模（KIM）在高β时不稳定，而离子温度梯度模在低β时不稳定，其中β是等离子体动压与磁压的比值。KIM的β阈值远低于正剪切等离子体中动力学气球模（KBM）的β阈值，但在不利曲率区KIM和KBM都很强，且KIM和KBM具有相同的宇称。非线性模拟表明，KIM饱和通过激发强纬向流和低环模数的波动。尽管KIM湍流的线性增长率远高于KBM湍流，但KIM湍流的振幅与KBM湍流的振幅相似。这是因为在低环模数下，反向剪切等离子体中的纬向流和波动的激发比正向剪切等离子体中的强。另一方面，KIM湍流引起的能流和粒子流大约是KBM湍流引起的能流和粒子流的两到三倍。
The nonlinear evolution of electromagnetic instabilities in reversed shear plasmas is investigated by means of global gyrokinetic simulations. It is found that the kinetic infernal mode (KIM), which is a pressure-driven instability with low to intermediate toroidal mode number excited in a region of low magnetic shear, is unstable at high β, while the ion temperature gradient mode is unstable at low β, where β is the ratio of the plasma kinetic pressure to the magnetic pressure. The β threshold of the KIM is much lower than that of the kinetic ballooning mode (KBM) appearing in a normal shear plasma, while both the KIM and KBM are strong at the unfavorable curvature region, and the KIM has the same parity as the KBM. Nonlinear simulations show that the KIM gets saturated by exciting strong zonal flows and fluctuations of low toroidal mode number. The amplitude of the KIM turbulence is similar to that of the KBM turbulence in spite of the fact that the linear growth rate of the KIM is much higher than that of the KBM. This is because the excitation of zonal flows and fluctuations at low toroidal mode number is stronger in the reversed shear plasma than that of the normal shear plasma. On the other hand, the energy flux and particle flux due to the KIM turbulence are about two or three times larger than those by the KBM turbulence.