RFQ冷却器SHIRaC的研制：束流传输和核化
Development of the RFQ Cooler SHIRaC: beam transport and nuclearization
摘要：
开发了名为SHIRaC的新型制冷机。作为SPIRAL 2设施的一部分，SHIRaC旨在处理和冷却具有大发射度（高达80 pi.mm.mrad）和高电流（高达1 uA）的典型SPIRAL 2光束。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的纵向能量扩散）并传输超过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。后者出现在射频出口处，并随着射频参数（射频电压的频率和幅度）而增加。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。使用这种方法，有可能改善冷却的束质量，并且对于高达1 μ A的束电流，达到1 eV的纵向能量扩展和大约1.75 π mm mrad的横向几何发射度。从SHIRaC到HRS的冷却束的运输已经完成了与静电四极三重态。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 the new RFQ Cooler, called SHIRaC, was carried out. As a part of SPIRAL 2 facility, SHIRaC aims to handle and cool typical SPIRAL 2 beams with large emittances (up to 80 pi.mm.mrad) and high currents (up to 1 uA). Its purposes are to enhance as much as possible the beam quality (transverse geometric emittance of less than 3 pi.mm.mrad and 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 term of the emittance. The energy spread is very far from expected values. It is sensitive to the space charge and the buffer gas diffusion and more importantly to the RF field derivative effect. The latter arises at the RFQ exit and increases with the RF parameters (the frequency and the amplitude of the RF voltage). 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 this method, it becomes possible to improve the cooled beam quality and to reach 1 eV of longitudinal energy spread and around 1.75 π.mm.mrad of transverse geometric emittance for beam currents going up to 1 uA. The transport of the cooled beam from SHIRaC 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 aiming to avoid the escape of any nuclear matter from the SHIRaC beamline are studied.
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