Capture of intense heavy ion beams with RFQ electrodes

为了在RFQ电极的空间电荷效应极限范围内捕获激光等离子体中的强重离子，进行了实验和仿真研究。研究结果使我们能够设计出一种能够处理强碳4+束的RFQ电极和一种激光等离子体离子提取装置。我们目前正在对萃取装置进行优化，并仍在提高高电荷重离子产生的最大电流。最新的结果显示，碳梁为65毫安。去年8月在德国吕贝克举行的“2004年线性加速器会议”上报告了我们的成果。我们的报告作为大电流重离子生产新技术在大会的总结报告中被重点讨论。在实验中，我们考察了RFQ场强度与捕获离子电流之间的关系。考虑空间电荷效应和RFQ场约束力的模拟结果很好地解释了这一结果。实验和模拟结果表明，叶片间电压为120 kV时，碳4+束的捕获效率最高。叶片间电压为63 kV时，只能加速碳6+的完全剥离。我们建立了一种可以诱导高纯度高电荷重离子的技术。我们还利用RFQ通道中扩展速度的变化，成功地将光束的脉冲长度从1微秒延长到10微秒。较长的脉冲长度将适用于大型同步加速器。

To capture intense heavy ions in laser plasmas up to a limit of space charge effect in RFQ electrode, experimental and simulation studies have been done. The results enabled us to design a new RFQ electrode which can handle intense carbon 4+ beam and an ion extraction devise from a laser plasma. We are currently in optimization process of the extraction devise and are still improving a maximum current of the highly charged heavy ion production. The latest result shows 65 mA of carbon beam. Our achievements was reported at "linear accelerator conference 2004" in Lubeck, Geramany last August. Our report was focused as new technique of high current heavy ion production at the summary talk in the conference.In the experiments, we examined the relationship between the strength of RFQ field and the captured ion current. This results were well explained by the simulations which took the space charge effect and the confinement force of the RFQ field into account. Both the experiment and the simulation showed that the carbon 4+ beam was captured by an inter-vane voltage of 120 kV most efficiently. Also it was found that the inter-vane voltage of 63 kV could only accelerated fully stripped carbon 6+ beam. We established the technique which could induce intense highly charged heavy ions at high purity.We also succeeded to extend pulse length of the beam from 1 micro s to 10 micro s using a variation of expanding velocities in the RFQ channel. The longer pulse length will fit to a large size synchrotron accelerators.