Magnetic flux ropes have been successfully created with plasma guns in the newly commissioned PHAse Space MApping (PHASMA) experiment. The flux ropes exhibit the expected m = 1 kink instability. The observed threshold current for the onset of this kink instability is half of the Kruskal–Shafranov current limit, consistent with predictions for the non-line tied boundary condition of PHASMA. The helicity, paramagnetism, and growth rate of the observed magnetic fluctuations are also consistent with kink instability predictions. The observed fluctuation frequency appears to be a superposition of a real frequency due to a Doppler shift of the kink mode arising from plasma flow ($\sim 2$ kHz) and a contribution from a wave mode ($\sim 5$ kHz). The dispersion of the wave mode is consistent with an Alfvén wave. Distinct from most previous laboratory studies of flux ropes, the working gas in PHASMA is argon. Thus, the ion cyclotron frequency in PHASMA is quite low and the frequency of the Alfvénic mode plateaus at $\sim 0.5$ of the ion gyro frequency with increasing background magnetic field strength.

中文翻译：

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PHASMA中扭结不稳定性激发的Alfvénic模式

在最近进行的PHAse Space MApping（PHASMA）实验中，等离子体枪已成功创建了磁通绳。助焊剂绳表现出预期的m  =  1扭结不稳定性。观察到的这种扭折不稳定性开始的阈值电流是Kruskal–Shafranov电流极限的一半，与对PHASMA的非线性约束边界条件的预测一致。所观察到的磁波动的螺旋度，顺磁性和增长率也与扭折不稳定性预测一致。由于等离子流引起的扭结模式的多普勒频移，观察到的波动频率似乎是真实频率的叠加（$〜\mathrm{2个}$ kHz）和波动模式的贡献（$〜5$千赫）。波模的色散与Alfvén波一致。与以往大多数磁通绳的实验室研究不同，PHASMA中的工作气体为氩气。因此，PHASMA中的离子回旋加速器频率非常低，Alfvénic模态平台的频率为$〜0.5$ 陀螺频率随背景磁场强度的增加而变化。