储存环强流和弱流离子束冷却研究

Along with further study of various physical experiments in the two rings and their three terminals at the Cooler Storage Rings of Heavy Ion Research Facility in Lanzhou, high-quality intensive ion beam accumulation in the main ring and lower momentum spread of secondary radioactive nuclear beam cooling in the experimental ring was required to improve the efficiency and accuracy of measurement in experiments. Therefore, researches on beam accumulation at high intensity in the main ring and electron cooling rate at the experimental ring becomes an urgent need. It was found in Δp/p∝Nξ experiment as electron cooled ion beam decaying that the power exponent ξ linearly depended on the minimum momentum spread whereas its theoretical explanation is not clear untill now. This project intends to increase beam intensity in the main ring by adjusting electron beam profile within cooling stage and accumulation respectively, i.e. cooling with solid electron beam at low ion beam intensity and accumulation with hollow electron beam at high intensity, and by heating cold beam core with transverse RF exciter to avoid "over cooling". The formation process of cold beam core and its impact on beam cooling and accumulation, and variation of electron cooling rate and intra-beam scattering effect will be studied as well. Particularly, the characteristics of power component ξ would be investigated through experiments. The research results will contribute to improving cooling and accumulation limit with the help of electron cooler. Furthermore, the new planning high intensity Heavy Ion Accelerator Facility will benefit from this research.

随着兰州重离子加速器冷却储存环及各终端物理实验研究的深入，实验用户要求储存环能够提供更高强度的高品质离子束流或更小动量分散的弱流次级核束以提高物理实验效率和测量精度。在主环研究高品质强流束的冷却累积和在实验环研究弱流次级束的电子冷却率成为冷却储存环现今运行中迫切需要探索的关键课题。主环电子冷却实验研究发现，Δp/p∝Nξ关系式中的幂指数ξ线性地依赖于离子束所能冷却到的最小动量分散，而ξ背后的物理含义尚不明确。本项目拟通过分段调变电子束密度分布，在冷却累积起始阶段和高流强累积阶段分别侧重冷却和累积，采用横向RF激励加热冷离子束核避免"过冷却"等途径来提高束流累积强度；研究高密度束核的形成过程及其对冷却累积的限制；研究电子冷却率和束内散射效应在冷却累积中的变化；将理论和结合实验深入研究幂指数ξ的物理含义。该项目研究将有利于极限情况下两环电子冷却性能的提高，为十二五强流重离子研究装置预研提供参考

本项目在兰州重离子加速器冷却储存环（CSR）以提高物理实验效率和测量精度的需求，在国家十二五大科学工程——强流重离子研究装置（HIAF）以预研高密度强流冷离子束制备为背景，研究极限情况下，CSR电子冷却在高密度高流强离子束冷却累积和弱流离子束在冷却中受到的限制，探索冷离子束在储存环内的运动规律，以及用脉冲电子束冷却离子束的可行性。本项目初步实验研究了离子束在CSR冷却累积中的束流运动不稳定性，以及电子冷却率和束内散射率等参数变化；在合作实验中，验证了CSR脉冲电子束冷却的可行性，并研究了冷却后脉冲离子束的相关参数；CSR主环和实验环存储离子束的稳定性提高和能散降低，使高精度谱学物理实验的测量精度明显提高。本项目研究结果将利于探索提升离子储存环性能的有效途径，为HIAF高精度环形谱仪的电子冷却装置和电子-离子复合共振谱仪国产化研制提供实际知识经验积累和人才培养。