残余气体对LIA束流发射度的影响
Scattering effects of residual gas and RMS emittance growth in DragonI LIA
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摘要: 把残余气体散射作为一种各向同性微扰力引入轴对称直流带电粒子束的均方根包络方程，从中得到了气体散射作用导致束流发射度增长的表达式。根据理论研究结果，结合“神龙一号”加速器束流传输系统的设计参数，计算了气体散射作用引起的发射度增长。结果表明，在束流传输系统的真空度高于3×10-4Pa时，残余分子的散射作用可以忽略不计。5×10-4Pa的真空指标是可以接受的。讨论了抑制残余气体分子散射作用的措施，在螺线管线圈能力许可的情况下，采用强磁场小半径传输有利于抑制残余气体散射导致的发射度增长。Abstract: In this paper, the multiple scattering effects of residual gas as isotropic disturbing forces, are introduced into the RMS envelope equation of cylindrically symmetric DC electron beams, so that the expression of emittance growth due to the scattering is obtained. Referring to the design parameters of beam transport system of DragonI LIA, the emittance growth is calculated. The result shows that the emittance growth due to gas scattering could be neglected if the pressure of vacuum tube is less than 3×１０－４Pa. And the measures to restrain the scattering effects are discussed．
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