Study of Plasma Neutralizer Cell for Negative Ion Beam

In the design of negative-ion based neutral beam injection （NBI）系统，neutralization efficiency from ion to neutral beam can improved by utilizing plasma neutralizerIn the case of gas neutralizerconversion efficiency is 59% maximum. In the case of plasma neutralizer，efficiency of 70%可以成就，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 ionizationratio,这是为了生产plasma at low pressure with using a container of good confinement. Forthat purpose,made a cylindrical discharge with vessel of the size of 310mm in diam and 1400mm in length withcusp magnetic field. Discharge characteristics and plasma confinement properties were studied usinghydrogen,argon和xenon as working gas with arc discharges by filaments.这是发现在gas的情况pressure higher than 0.2 Pa, the plasma density was higher than n>10but 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.它是however difficult to keepstable plasma discharge at the gas pressure less than 0.1 Pa，hence the plasma efficiency of the confinement properties of the vessel determines minimum gaspressure and the highest ionization. In this study，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.这也曾发现plasma density andionization ratio could be higher with improving the confinement. We obtained prospect of the plasmaneutralizer which would have an enough density and the ionization ratio of more than 10%。

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%.