Underwood Thomas C, Loebner Keith T K, Miller Victor A, Cappelli Mark A
High Temperature Gasdynamics Laboratory, Stanford University, Stanford, California, 94305, USA.
SeekOps, Inc., Austin, Texas 78745, USA.
Sci Rep. 2019 Feb 22;9(1):2588. doi: 10.1038/s41598-019-39827-6.
Instabilities play a prominent role in determining the inherent structure and properties of magnetized plasma jets spanning both laboratory and astrophysical settings. The manner in which prominent unstable modes dynamically evolve remains key to understanding plasma behavior and control. In astrophysical phenomena, self-similar jets are observed to propagate over vast distances while avoiding breakup caused by unstable mode growth. However, the production of stable dense plasma jets in the laboratory has been limited by the onset of unstable modes that restrict jet lifetime, collimation, and scalability. In this work, we visualize the formation of stable laboratory-generated, dense, super-magnetosonic plasma jets in real time, and we identify an underlying mechanism that contributes to this behavior. The current-driven plasma jets generated in our experiments form a flowing Z-pinch, which is generally unstable to the m = 1 kink instability. Our results indicate that a stable dense plasma jet can be maintained for timescales over which a steady pinch current can be sustained, even at levels which would otherwise lead to rapid unstable mode growth and resultant pinch disassembly.
不稳定性在决定跨越实验室和天体物理环境的磁化等离子体喷流的固有结构和特性方面起着重要作用。显著不稳定模式的动态演化方式仍然是理解等离子体行为和控制的关键。在天体物理现象中，观察到自相似喷流能在很长距离上传播，同时避免因不稳定模式增长而导致的破裂。然而，在实验室中稳定致密等离子体喷流的产生一直受到不稳定模式的限制，这些模式限制了喷流的寿命、准直度和可扩展性。在这项工作中，我们实时可视化了实验室产生的稳定、致密、超磁声等离子体喷流的形成，并确定了促成这种行为的潜在机制。我们实验中产生的电流驱动等离子体喷流形成了一个流动的Z箍缩，它通常对m = 1扭结不稳定性不稳定。我们的结果表明，即使在否则会导致快速不稳定模式增长并导致箍缩解体的水平下，稳定致密的等离子体喷流也能在稳定箍缩电流能够维持的时间尺度上得以维持。
