Capture of intense heavy ion beams with RFQ electrodes

为了在激光等离子体中捕获强流重离子，使其达到空间电荷效应的极限，对激光等离子体中的重离子进行了实验和模拟研究。这一结果使我们能够设计出一种新的能处理强流碳离子束的阴极电极和一种从激光等离子体中提取离子的装置。我们目前正在优化提取装置，并仍在提高高电荷重离子产生的最大电流。最新结果显示碳束电流为65 mA。我们的研究成果在去年8月德国吕贝克举行的“2004年直线加速器会议”上发表。我们在会议的总结报告中重点介绍了强流重离子产生的新技术，在实验中，我们研究了强流场强度与俘获离子流之间的关系。考虑了空间电荷效应和电场约束力的模拟结果很好地解释了这一现象。实验和模拟结果均表明，当叶片间电压为120 kV时，碳4+离子束的捕获效率最高。同时发现63kV的叶片间电压只能加速完全剥离的碳6+束流。我们建立了一种高纯度强流高电荷态重离子束的诱导技术，并通过改变束流通道的扩展速度，成功地将束流脉冲宽度从1 μ s扩展到10 μ s。较长的脉冲宽度将适合于大型同步加速器。

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.