用集团运动的观点来研究回流离子问题  

A New Physical Image on Backstreaming Ions Study

作　　者：龙继东[1] 林郁正[1] 石金水[2] 禹海军[2] 

机构地区：[1]清华大学工程物理系,北京100084 [2]中国工程物理研究院,绵阳621900

出　　处：《高能物理与核物理》2005年第12期1185-1189,共5页High Energy Physics and Nuclear Physics

基　　金：国防科技基础研究项目资助

摘　　要：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.这些离子在电子柬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.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.

关 键 词：束靶相互作用 回流离子 离子鞘层 电子束聚焦 

分 类 号：O572.2[理学—粒子物理与原子核物理]