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Spontaneous Formation of Ion Holes and Ion Beams in Expanding Plasmas

机译：膨胀等离子体中离子孔和离子束的自发形成

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摘要

Presented here are direct, spatially resolved measurements of the spontaneous formation of a steady-state, ion accelerating structure and an ion hole in the plume of an expanding, low- pressure plasma. Ion velocity distribution function (IVDF) measurements, obtained with laser induced fluorescence, are taken parallel and perpendicular to the background magnetic field in an argon helicon plasma. The parallel IVDFs show an ion beam with v ≈ 8,000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. At the periphery of the ion beam, bipolar, magnetic field-aligned electric field structures, ion holes, form and accelerate ions across the ambient magnetic field. Multi-species plasmas provide further evidence that the ion acceleration mechanism is not a true double layer (DL). These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas. A new paradigm for the spontaneous formation of ion accelerating structures in expanding plasmas is presented.
机译：本文介绍的是直接，空间分辨的测量值，用于自发形成稳态的离子加速结构和膨胀的低压等离子体羽流中的离子孔。用激光诱导的荧光获得的离子速度分布函数（IVDF）测量值是平行于且垂直于氩氦等离子体中的背景磁场进行的。平行的IVDF显示出具有v＆ap;的离子束。 8,000 m / s顺流而下，并限制在排放中心。在LIF信号消失之前，沿扩展轴可测量离子束数十厘米，这很可能是离子束亚稳猝灭的结果。平行离子束速度减慢，与对测得的平行电场的预期一致。垂直的IVDF显示离子种群具有径向向外的流动，该流动随离等离子体轴的距离而增加。在离子束的外围，双极磁场定向的电场结构，离子孔形成并加速了整个环境磁场中的离子。多物种等离子体进一步提供了离子加速机制不是真正的双层（DL）的证据。这些测量结果表明，至少需要二维模型，甚至可能是完全三维模型，才能准确描述膨胀等离子体中离子束的自发加速。提出了在膨胀等离子体中自发形成离子加速结构的新范例。

著录项

  • 作者

    Aguirre, Evan M.;

  • 作者单位

    West Virginia University.;

  • 授予单位 West Virginia University.;
  • 学科 Physics.;Plasma physics.
  • 学位 Ph.D.
  • 年度 2018
  • 页码 134 p.
  • 总页数 134
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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