用集团运动的观点来研究回流离子问题

建立在单粒子运动学基础上的回流离子理论预测: 强流电子束轰击在 辐射转换靶上可能产生正离子. 这些离子在电子束空间电荷场作用下 回流, 会造成电子束过聚焦, 改变焦斑大小, 从而影响X光机的照相分辨率. 然而大量的实验没有发现相关的现象. 本文分析认为, 电子束 打靶时, 在靶表面可能会形成离子鞘层过渡区. 该区域可以抵消束流空间 电荷场对回流离子的驱动作用, 因此, 回流离子可能以等离子体集团扩散的 方式运动. 这种物理图像得到的结论是离子对聚焦的影响可忽略, 和已有的 实验结果相吻合.

A New Physical Image on Backstreaming Ions Study

Backstreaming ions issue is a major concern for new generation radiography facilities based on LIA (linear induction accelerator). Its theory based on dynamics of single particle driving by beam charge field predicts that the ions could bring adverse effect on beam focus, resulting in degrade of radiography resolution. The predicted phenomena have not been observed until now. A new physical image on ions movement is presented here. Through analysis, it is found that an ions sheath transition zone could form between the target surface and the plasma. The sheath zone could counteract the beam space charge field applied on the positive ions. So using mass movement of diffusion to study ions behavior may be more proper. A verification experiments on the new image is also given in the end.