Study of Plasma Neutralizer Cell for Negative Ion Beam

负离子束等离子体中和器的研究

• 批准号: 10558069
• 负责人: HORIIKE Hiroshi
• 金额: $ 7.55万
• 依托单位: Osaka University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (B)
• 财政年份: 1998
• 资助国家: 日本
• 起止时间: 1998 至 1999
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10558069/
• 关键词: negative ion source; neutralization efficiency; plasma; nuclear fusion; heating; magnetic multi-pole ion source; bucket ion source; ionization ratio; 負イオンビーム; プラズマ中性化セル; アーク放電

In the design of negative-ion based neutral beam injection (NBI) system, neutralization efficiency from ion to neutral beam can be improved by utilizing plasma neutralizer. In the case of gas neutralizer, the conversion efficiency is 59% maximum. In the case of plasma neutralizer, efficiency of 70% can be achieved, because of reduced double stripping reaction in which a negative ion is converted to a positive ion. This requires the plasma with as high ionization ratio as possible (10%>).To get high ionization ratio, it is important to produce plasma at low pressure with using a container of good confinement. For that purpose, we made a cylindrical discharge with vessel of the size of 310mm in diam and 1400mm in length with cusp magnetic field. Discharge characteristics and plasma confinement properties were studied using hydrogen, argon and xenon as working gas with arc discharges by filaments. It is found that in the case of gas pressure higher than 0.2 Pa, the plasma density was higher than n>10ィイD111ィエD1 cmィイD1-3ィエD1, but the ionization ratio was smaller than 1%. But, in the case of the gas pressure under 0.2 Pa, the ionization ratio increased rapidly as the pressure decreased. It is however difficult to keep the stable plasma discharge at the gas pressure less than 0.1 Pa, hence the plasma efficiency of the confinement properties of the vessel determines minimum gas pressure and the highest ionization. In this study, the pressure of 0.03 Pa was the lowest and the ionization ratio of 1.3% for hydrogen, 3.2% for argon and 8% for xenon were achieved. It was also found that the plasma density and ionization ratio could be higher with improving the confinement. We obtained prospect of the plasma neutralizer which would have an enough density and the ionization ratio of more than 10%.

在负离子中性束注入(NBI)系统的设计中，利用等离子体中和器可以提高从离子到中性束的中和效率。在气体中和器的情况下，转换效率最高为59%。在等离子体中和器的情况下，由于减少了将负离子转化为正离子的双溶出反应，效率可达到70%。这就要求等离子体具有尽可能高的电离率(10%)。要获得高电离率，重要的是使用良好的限制条件在低压下产生等离子体。为此，我们制作了直径310 mm、长1400 mm的圆柱形放电容器，并施加尖峰磁场。以氢、氩、氙气为工作气体，采用灯丝弧光放电，研究了放电特性和等离子体约束特性。结果表明，在气压高于0.2Pa时，等离子体密度高于n&gt；10ィイD111ィエD_1 cmィイD_1-3ィエD_1，但电离率小于1%。但是，当气压低于0.2Pa时，电离率随着气压的降低而迅速增大。然而，在气压低于0.1Pa时很难保持稳定的等离子体放电，因此容器的约束性质决定了最小气压和最高电离的等离子体效率。在本研究中，最低气压为0.03Pa.获得氢气的电离率为1.3%，Ar的电离率为3.2%，氙气的电离率为8%.研究还发现，随着约束条件的改善，等离子体密度和电离率都会提高。展望了密度足够大、电离率在10%以上的等离子体中和器的前景。