球形托卡马克绝热不变性的破坏
Breakdown of adiabatic invariance in spherical tokamaks
摘要：
球形托卡马克中的热离子有两个绝热不变量：磁矩和纵向不变量。对于热离子，磁场强度在陀螺周期上的变化可以变得足够大，从而导致绝热不变性的破坏。磁矩对扰动比纵向不变量更敏感，并且存在一个中间状态，即超绝热性，其中纵向不变量保持绝热，但磁矩不保持绝热。超绝热离子的运动仍然是可积的，从而保持了约束。然而，在阈值能量以上，纵向不变量也变得非绝热，并且随着运动变得混沌而失去约束。我们预测束离子在当今的球形托卡马克是超绝热的，但在建议燃烧等离子体球形托卡马克融合阿尔法是非绝热的。
英文摘要：
Thermal ions in spherical tokamaks have two adiabatic invariants: the magnetic moment and the longitudinal invariant. For hot ions, variations in magnetic-field strength over a gyro period can become sufficiently large to cause breakdown of the adiabatic invariance. The magnetic moment is more sensitive to perturbations than the longitudinal invariant and there exists an intermediate regime, super-adiabaticity, where the longitudinal invariant remains adiabatic, but the magnetic moment does not. The motion of super-adiabatic ions remains integrable and confinement is thus preserved. However, above a threshold energy, the longitudinal invariant becomes non-adiabatic too, and confinement is lost as the motion becomes chaotic. We predict beam ions in present-day spherical tokamaks to be super-adiabatic but fusion alphas in proposed burning-plasma spherical tokamaks to be non-adiabatic.
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