低能强流质子束空间电荷补偿度研究(英文)

Key words: 
• space charge effect /
• neutralization level /
• three-grid energy analyzer

Abstract: 

对于低能强流离子束来说，空间电荷效应的存在将导致束流发散、发射度增加等一系列问题，从而降低束流品质。幸运的是，当束流由离子源引出通过低能传输线时会与其中的剩余气体发生电离反应，产生二次电子与二次离子；二次电子在束流自身产生的电场作用下，在束流中积累并中和部分空间电荷，达到抑制空间电荷效应的效果。为了测量空间电荷中和程度，中国科学院近代物理研究所研制了一台三栅网式能量分析仪用以测量电离过程中产生的二次离子能量来间接计算空间电荷中和度。实验结果表明，对于40 keV, 18.5 mA的质子束，真空度为1.510*3 Pa 时得到最佳补偿度；真空度一定的情况下，空间电荷补偿度随束流流强增加而变大。

For high-intensity low-energy ion beams, space charge effect is a main cause of beam divergence  and emittance growth. Fortunately, residual gas molecules in the drift space tend to be ionized and neutralize the beam space charge spontaneously. The level of Space Charge Neutralization (SCN)
is measured through the detection of created secondary ion energy distribution in the beam region. A so-called non-interceptive Three-grid Energy Analyzer (TEA) has been designed and manufactured at Institute of Modern Physics, Chinese Academy of Sciences (IMP). This paper will present the details
of the TEA detector and the application to diagnose proton beam SCN level in the Low Energy Beam Transport (LEBT) line. As a preliminary result, for an 18.5 mA proton beam a best compensating point appears at the vacuum pressure of 1.510*3 Pa. And the neutralization level is advanced with the
growth of beam current in a constant vacuum pressure.