在电子冷却存在情况下储存环中束流不稳定及其抑制的研究

From the experience of commissioning and operation in the past seven years, The most serious factor of the influence on the ion beam maximum accumulated ion beam intensity and the minimum momentum spread in the Cooler Storage Ring of Heavy Ion Research Facility in Lanzhou was the beam instability, and it brought on the shortening of beam lifetime and beam loss. It became the bottleneck of improvement on the beam quality and upgrade of the performance. The more intense, the more high precision and the more stable ion beam were asked by the physics experiments users on the storage ring. The beam instability presents different effects in the different facilities. The mechanism of beam instability was not revealed in ion beam dynamics, the reason of instability was not declared from the aspects of accelerator physics, and more effective method to suppress the instability was not discovered. The systematic investigation on the mechanism and principle of the beam instability in detail were planned with help of the simulation and compared with the experiments. On the base of the results of simulation, some effective and helpful methods were proposed to suppress the ion beam instability. A new idea was introduced in this proposal. A novel method was proposed in this project. The electrostatic field produced by the space charge of electron beam in the cooler by means of modulation on the voltage of control electrode in the electron gun will act as a traveling wave in the cooling section. This new way will be attempted to suppress the ion beam instability in the presence of electron cooling device. Two functions were combined in the one electron beam. The more stable, the more intense and more precise heavy ion beam was expected in HIRFL-CSR. The constructive proposal for upgrade was suggested based on these results. These results will be helpful for the upgrade and improvement of CSR in the near future and provide basis for further development.

在过去近七年的HIRFL-CSR调试运行中，发现影响主环最大累积离子束流强和实验环最小动量分散的主要因素为束流的不稳定性。不稳定导致束流寿命短、损失快，不稳定成为CSR束流品质和性能提高的瓶颈。CSR中束流不稳定产生的机理尚不明确，束流不稳定的原因及有效的抑制方法亟待进一步深入研究，从而为物理实验用户提供更高流强和精度的离子束，提供更稳定的离子束。本项目将基于前期实验研究结果，通过模拟计算，有针对性地揭示CSR上束流不稳定发生的机理及规律，通过研究深入了解这些不稳定现象的束流物理内部机制，提出可行的、有效的抑制束流不稳定的方案。其次本项目拟采用调制电子冷却中电子束的方法，利用电子束产生的空间电荷场对离子束产生作用，探索抑制离子束的不稳定性的新方法，实现一束两用的目的。本项目的研究旨在提高HIRFL-CSR的性能，为用户提供高精度、高分辨的重离子束，并为下一步机器性能的全面提升奠定理论基础。

本项目旨在采用调制电子束产生的电子束团来抑制运行在储存环中的重离子束在不同阶段的不稳定性，期望能够通过这种措施，提高累积流强，降低动量分散，减少离子束的损失，延长离子束的寿命，为物理实验提供高品质长寿命高精度的离子束。.本项目从电子束的调制方案设计、不稳定的分析，通过模拟和实验两种手段，期望抑制注入阶段的不稳定性来提高累积离子束流强；抑制储存阶段的不稳定性来减低离子束的动量分散、提高离子束的品质；抑制衰减阶段的不稳定来延长离子束的寿命。.经过对以往近十二年来储存环上大量实验数据的认真仔细分析，发现储存环中离子束的不稳定性来自加速器的硬件参数的不稳定。来自束流本身的不稳定因素很小，原因在于储存环中离子束的流强较弱，储存环中的粒子数不足够多，离子束的发射度不足够小，离子束的纵向长度不足够短，也就是储存环中离子束的密度不足够高。.在实验室设计制作并完成了电子束调制平台，设计研发了电子束调制系统，建立了测量系统，在电子冷却系统电子枪的控制极上得到了高压脉冲，由此可以在电子枪上得到相同的电子束团脉冲，实现了电子束由直流到脉冲的调制。.观测了束流不稳定的现象，研究了不稳定发生的过程，从时间尺度上分析了束流不稳定持续的时间和强度，研究了束流不稳定发生的规律，剖析了产生不稳定的原因，对储存环中重离子束的不稳定现象有了全面、清楚的认识和理解，给出了合理可行的抑制方案，从技术角度实现了项目申请书中提出的抑制方案，在储存环中采取了抑制束流不稳定的措施，改善了束流在储存环中的运动状态，完成了预期的研究目标。.开创了电子冷却研究的新方向，增大了电子冷却的应用范围，拓展了电子冷却研究的深度和广度，形成了以脉冲电子束电子冷却为主的具有独立特色的研究方向，培养壮大了电子冷却研究队伍，加深了对不同离子束流强情况下电子冷却的理解。.本项目的研究结果表明，影响强流高密度重离子束在储存环中寿命的关键因素是束内散射。