法拉第杯测量电子束中离子的回流与等离子体羽流的碰撞
Faraday Cup Measurements of Ions Backstreaming into a Electron Beam Impinging on a Plasma Plume*
摘要：
基于感应加速器的下一代射线照相机预计将产生多个高强度的小直径X射线点。研究电子束与在X射线转换器和束线隔板处产生的等离子体的相互作用的实验正在劳伦斯利弗莫尔国家实验室（LLNL）使用6 MeV、2 kA实验测试加速器（ETA）电子束进行。人们关心的物理问题可以分为两类。随后的射束脉冲与早期脉冲撞击X射线转换器或隔膜产生的膨胀等离子体羽流的相互作用，以及涉及通过射束脉冲的头部从等离子体中提取轻离子的更微妙的效果。这些轻离子可能是由于束管或转换器表面上的污染物，或者对于后续脉冲，是由于转换器材料中的污染物。束流的空间电荷抑制可以将轻离子加速到几mm/ns的速度。当离子移动通过入射脉冲的主体时，射束将被箍缩，导致在转换器之前的移动焦点和随时间变化的X射线斑点。在X射线转换器的束产生的等离子体的研究以前已经报道。在本文中，我们描述了法拉第杯测量进行检测和定量的回流离子流的ETA束脉冲撞击在预制等离子体。* 这项工作是在美国能源部的赞助下，由加利福尼亚大学劳伦斯利弗莫尔国家实验室根据合同号W-7405-Eng-48进行的。
英文摘要：
The next generation of radiographic machines based on induction accelerators is expected to generate multiple, small diameter x-ray spots of high intensity. Experiments to study the interaction of the electron beam with plasmas generated at the x-ray converter and at beamline septa are being performed at the Lawrence Livermore National Laboratory (LLNL) using the 6-MeV, 2-kA Experimental Test Accelerator (ETA) electron beam. The physics issues of concern can be separated into two categories. The interaction of subsequent beam pulses with the expanding plasma plume generated by earlier pulses striking the x-ray converter or a septum, and the more subtle effect involving the extraction of light ions from a plasma by the head of the beam pulse. These light ions may be due to contaminants on the surface of the beam pipe or converter, or, for subsequent pulses, in the material of the converter. The space charge depression of the beam could accelerate the light ions to velocities of several mm/ns. As the ions moved through the body of the incoming pulse, the beam would be pinched resulting in a moving focus prior to the converter and a time varying x-ray spot. Studies of the beam-generated plasma at the x-ray converter have been previously reported. In this paper we describe Faraday cup measurements performed to detect and quantify the flow of backstreaming ions as the ETA beam pulse impinges on preformed plasma. * This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.
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