微波驱动体效应负氢源的关键技术研究

The development of high-intensity negative hydrogen ion source with non-cesium is of great importance in the fields of accelerator technology, nuclear energy, medical science and materials science. The 2.45 GHz microwave driven volume H- ion source, which produces negative hydrogen ions based on the microwave discharge, have many advantages such as simple structure, long lifetime, low cost, and so on. Preliminary studies on the microwave driven H- ion source have been done in some labs. However, the beam current of this source type is only several mA, which is unable to meet the requirements of the high intensity accelerators. This research will carry out on microwave driven volume effect negative hydrogen ion source with non-cesium for the purpose of beam current improvement. The studies will focus on the constraint of high energy electrons produced in microwave plasma, the microwave blocking within low energy region, the collar structure and the electron absorption around the extraction area, which can help to improve the efficiency of H- producing. Meanwhile, simulation and experimental studies about the beam extraction system will be carried out to decrease the electron proportion and to abtain a high quality H- beam. Through this research, the key technologies of H- generation and handling will be clear, and the 2.45 GHz microwave driven volume ion source will become a competitive choice for the high current H- accelerators in the world.As expected, more than 20 mA of pure H- ion beam will be produced from the cesium free microwave driven H- ion source with the normalized rms emittance less than 0.2 pi.mm.mrad.

开展无铯强流负氢离子源研究对加速器、核能源、医学及材料科学具有重要意义。微波驱动体效应负氢离子源基于微波放电来产生负氢离子，具有结构简单、寿命长、造价低廉等优点。目前，国际上已经开始了微波驱动体效应负氢源的相关研究，但引出流强仅有几mA，无法满足强流加速器的发展要求。本项目将以提高流强为目的，开展强流无铯微波驱动负氢离子源的研制。将重点研究微波等离子体所产的高能电子的约束、低能区的微波阻挡、肩（Collar）结构及引出区电子的偏转，以提高负氢离子的产生效率；并开展负氢离子源引出系统的模拟与实验研究，减小引出束流中的电子成分，确保引出负氢离子的束流品质。通过该项目的实施研制能满足加速器发展要求的微波驱动负氢离子源，总结负氢离子产生效率得以提高的关键技术。期望在50 keV能量下，引出大于20 mA的纯净H-离子束，且束流的归一化均方根发射度小于0.2 pi.mm.mrad。

本项目对体效应负氢离子的形成机理进行了深入研究，开展了磁帘场对高能电子和低能电子分离作用的理论分析，实验验证了离子源内气体分布对负氢离子的形成所产生的影响。在源体结构的优化方面，本项目分别从微波窗水冷结构的优化，肩结构的采用和优化研究，源体进气位置的对比研究，内衬材料的影响，电子偏转磁场的优化以及引出系统的改进等方面对微波驱动体效应负氢离子源进行了全面而细致研究。针对源体运行参数的优化，在本项目执行期间开展了进气量对负氢等离子体放电的影响研究。为了验证本项目离子源的优异性能，还开展了任意占空比的实验研究，引出束流可以从1%到100%（CW）连续变化。在上述研究的基础上，本课题组进行了新结构负氢离子源的再设计工作，并在新源加工完成后成功地进行了脉冲放电实验。目前，该项目负氢离子源可以在35kV下引出29mA的直流负氢流和45mA占空比为10%（100Hz/1ms）的脉冲负氢流，离子源的束流功率效率分别提高到29mA/kW（CW）和21.4mA/kW。离子源具有在直流/脉冲工作模式之间随意切换的能力。经过本课题组三年的努力，全面地完成了本项目的预期研究目标。