Magnetic field threshold for runaway generation in tokamak disruptions
Magnetic field threshold for runaway generation in tokamak disruptions
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DOI：
10.1063/1.3072980
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发表时间：
2009-02
影响因子：
2.2
通讯作者：
T. Fülöp;Håkan Smith;G. Pokol
中科院分区：
文献类型：
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作者：
T. Fülöp;Håkan Smith;G. Pokol
实验观测表明，在托卡马克破裂中产生逃逸电子存在一个磁场阈值。在这项工作中，研究了这一阈值的两个可能原因。对这些观测的第一个可能的解释是，失控的光束激发哨声波，在速度空间散射电子，阻止光束增长。最不稳定哨声波的增长率与磁场强度成反比。考虑到波的碰撞和对流衰减，可以推导出一个磁场阈值，低于该阈值就不会有逃逸。第二种可能的解释是，通过计算在感应环向电场扩散出等离子体之前可以产生多少逃逸电子而得到的实质失控产生的判据与磁场的关系。结果表明，即使在快速冷却的等离子体中，热尾的产生有望引起大量的逃逸粒子，哨声波也可以在一定磁场下阻止逃逸的形成，除非扰乱后温度很低。
Experimental observations show that there is a magnetic field threshold for runaway electron generation in tokamak disruptions. In this work, two possible reasons for this threshold are studied. The first possible explanation for these observations is that the runaway beam excites whistler waves that scatter the electrons in velocity space prevents the beam from growing. The growth rates of the most unstable whistler waves are inversely proportional to the magnetic field strength. Taking into account the collisional and convective damping of the waves it is possible to derive a magnetic field threshold below which no runaways are expected. The second possible explanation is the magnetic field dependence of the criterion for substantial runaway production obtained by calculating how many runaway electrons can be produced before the induced toroidal electric field diffuses out of the plasma. It is shown, that even in rapidly cooling plasmas, where hot-tail generation is expected to give rise to substantial runaway population, the whistler waves can stop the runaway formation below a certain magnetic field unless the postdisruption temperature is very low.