微型电子回旋共振离子源的全局模型

微型电子回旋共振(electron cyclotron resonance, ECR)离子源在紧凑型离子注入机、小型中子管、微型离子推进器等领域有着十分广泛的应用.为了深入认识微型ECR离子源的工作机理,本文以北京大学自主研制的一款微型氘离子源作为研究对象,以氢气和氘气放电形成的等离子体为例,发展了一种基于粒子平衡方程的全局模型.研究结果表明,该离子源束流成分与离子源的运行气压和微波功率有着很强的依赖关系.对于氢气放电等离子体,微波功率低于100 W时,离子源可以分别在低气压和高气压情况下获得离子比超过50%的H~+₂离子束和H~+₃离子束;当微波功率高于100 W时,可以在很宽的运行气压范围内,获得质子比超过50%的束流.因此,提高微波功率是提高微型离子源质子比的关键.对于氘气放电等离子体, 3种离子比例对运行气压和微波功率的依赖关系与氢气放电等离子体的规律基本一致.但是在相同的运行条件下, D~+比例比H~+比例高10%—25%.也就是说,在微型氘离子源的测试和优化过程中,可以利用氢气代替氘气进行实验,并将质子比测量结果作为相同条件下氘离...     

Practical 2.45-GHz microwave-driven Cs-free Hˉ ion source developed at Peking University

A practical 2.45-GHz microwave-driven Cs-free Hˉ source was improved based on the experimental Hˉ source at Peking University(PKU). Several structural improvements were implemented to meet the practical requirements of Xi'an Proton Application Facility(XiPaf). Firstly, the plasma chamber size was optimized to enhance the plasma intensity and stability. Secondly, the filter magnetic field and electron deflecting magnetic field were enhanced to reduce co-extracted electrons. Thirdly, a new two-electrode extraction system with farther electrode gap and enhanced water cooling ability to diminish spark and sputter during beam extraction was applied. At last, the direct Hˉ current measuring method was adopted by the arrangement of a new pair of bending magnets before Faraday cup(FC) to remove residual electrons. With these improvements, electron cyclotron resonance(ECR) magnetic field optimization experiments and operation parameter variation experiments were carried out on the Hˉ ion source and a maximum 8.5-mA pure Hˉ beam was extracted at 50 kV with the time structure of 100 Hz/0.3 ms. The root-mean-square(RMS) emittance of the beam is 0.25 Π·mm·mrad. This improved Hˉ source and extraction system were maintenance-free for more than 200 hours in operation.