等离子体密度对尾场加速中最优束流负载的影响  

The influence of plasma density on the optimal beam-loading in plasma wakefield acceleration

作　　者：黄开国 安维明 HUANG Kaiguo;AN Weiming(Department of Astronomy,Beijing Normal University,Beijing,China;Institute for Frontiers in Astronomy and Astrophysics,Beijing Normal University,Beijing,China)

机构地区：[1]北京师范大学天文系,北京 [2]北京师范大学天文与天体物理前沿科学研究所,北京

出　　处：《北京师范大学学报（自然科学版）》2024年第2期183-189,共7页Journal of Beijing Normal University(Natural Science)

基　　金：国家自然科学基金资助项目(12075030);北京师范大学引进人才科研启动经费资助项目(310432104,312200502503)。

摘　　要：探讨了当束团参数固定时,通过改变束团电荷量来改变束流的负载状态以达到最优束流负载条件,以及改变等离子体密度对束流负载特性的影响;通过实验发现,等离子体的入口和出口处均存在逐渐增加或降低的等离子体密度坡,并探究了该密度坡对束团相对能散的影响.利用QuickPIC对粒子的行为及其在等离子体中的演化状态进行了模拟;利用理论分析法对束团状态和相对能散的变化进行了综合分析和论证.结果表明:1)在传播方向上局部微调等离子体密度可降低尾随束团的相对能散;2)密度坡的存在会降低相对能散;3)改变等离子体密度,可实现欠负载、过负载,以及最优束流负载之间的切换,最终能散相较最优束流负载状态下的能散更低.In the beam driven plasma wakefield acceleration,the optimal beam-loading can be achieved by changing the total charge of the witness beam while keeping all other beam parameters the same.Under the optimal beam loading condition,the witness beam will have the minimal relative energy spread growth during the acceleration process inside the plasma.When the witness beam does not have the proper charge for the optimal beam loading,it will be either less loaded or over loaded inside the plasma wake.In this paper,we proposes that the beam-loading condition can be modified by changing the plasma density with fixed beam parameters.Furthermore,the final relative energy spread of the witness beam can be mitigated by using a longitudinally non-uniform plasma.These are shown in the simulation results that uses the QuickPIC code.In addition,we also show that the density ramps in the plasma wakefield accelerator experiments will not lead growth on trailing beam’s energy spread but will instead reduce it.

关 键 词：等离子体尾场加速 最优束流负载 密度坡 能散 粒子网格模拟 

分 类 号：TF806[冶金工程—有色金属冶金]