RFQ冷却器SHIRaC开发

摘要：

开发了一种名为SHIRaC的新型电子束冷却器，用于处理和冷却典型的大发射度（高达80 π.mm.mrad）和高电流（高达1 { \micro }A）的SPIRAL 2电子束。SHIRaC是法国GANIL实验室SPIRAL 2设施的一部分。其目的是尽可能地提高射束质量：小于3 π.mm.mrad的横向几何发射度和接近1 eV的纵向能量扩展，并且透射超过60%的离子。数值模拟和实验研究表明，只有在发射度方面才能达到所需的光束质量。能量分布与预期值相差甚远。它对空间电荷和缓冲气体扩散敏感，更重要的是对射频场的导数效应敏感。后者出现在阴极出口处，并随着以下RF参数而增加：施加到阴极电极的RF电压的频率和幅度。允许提高冷却光束质量的研究，主要是能量扩散减少，提出和讨论沿本文。它们包括在出口处实施一个小型的自动化系统。利用这些研究的进展，对于高达1 { \micro }A的束流，有可能提高冷却束质量，并达到1 eV的纵向能量扩展和小于1.8 π.mm.mrad的横向几何发射度。从引出部分的出口朝向HRS的冷却束的运输已经用静电四极三重态完成。模拟和第一次实验测试表明，超过95%的冷却光束可以达到HRS。最后，研究了防止核物质从SHIRaC束线逃逸的核化保护方法

英文摘要：

The development of a new RFQ Cooler, named SHIRaC, was carried out to handle and cool typical SPIRAL 2 beams of large emittances (up to 80 π.mm.mrad) and high currents (up to 1 {\micro}A). SHIRaC is a part of SPIRAL 2 facility at GANIL laboratory in France. Its purposes are to enhance as much as possible the beam quality: transverse geometric emittance of less than 3 π.mm.mrad and a longitudinal energy spread close to 1 eV, and to transmit more than 60 % of ions. Numerical simulations and experimental studies have shown that the required beam quality can be reached only in the term of the emittance. The energy spread is very far from expected values. It is sensitive to the space charge and buffer gas diffusion and more importantly to the RF field derivative effect. The latter arises at the RFQ exit and increases with the following RF parameters: the frequency and the amplitude of the RF voltage applied to the RFQ electrodes. Studies allowing to enhance the cooled beam quality, mainly the energy spread reduction, are presented and discussed along this paper. They consist in implementing a miniature RFQ at the RFQ exit. Using the development of these studies, it becomes possible to enhance the cooled beam quality and to reach 1 eV of longitudinal energy spread and less than 1.8 π.mm.mrad of transverse geometric emittance for beam currents going up to 1 {\micro}A. The transport of the cooled beam from the exit of the extraction section towards a HRS has been done with an electrostatic quadrupole triplet. Simulations and first experimental tests showed that more than 95 % of cooled beams can reach the HRS. Finally, developments related to the nuclearization protection methods aimed to avoid the escape of any nuclear matter from the SHIRaC beamline are studied

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