CERN的HIE-ISOLDE直线加速器高β四分之一波谐振腔横场不对称性补偿
Compensation of Transverse Field Asymmetry in the High-beta Quarter-wave Resonator of the HIE-ISOLDE Linac at CERN
摘要：
CERN的REX-ISOLDE放射性离子束（RIB）后加速器的超导升级将利用一个紧凑的晶格，包括四分之一波谐振器（QWR）和超导体，加速质量范围为2.5 < A/q < 4.5至超过10 MeV/u的束。短且独立定相的四分之一波长结构允许RIB在可变速度剖面上加速，并且在与螺线管聚焦耦合时提供无与伦比的纵向接受度。将螺线管结合到低温超导体中缩短了直线加速器，同时最大化了接受度，但是在存在不对称QWR场的情况下螺线管聚焦的应用可能对光束质量产生影响。在实验室参考系中，非对称光束的旋转产生有效发射度的增长。我们提出了修改的腔的几何形状，以优化的对称性的高β QWR的横向字段。一个跑道形的光束端口进行了分析和修改的内部导体的几何形状，这将使铌膜有效地溅射到腔表面上。
英文摘要：
The superconducting upgrade of the REX-ISOLDE radioactive ion beam (RIB) post-accelerator at CERN will utilise a compact lattice comprising quarter-wave resonators (QWRs) and solenoids, accelerating beams in the mass range 2.5 < A/q < 4.5 to over 10 MeV/u. The short and independently phased quarter-wave structures allow for the acceleration of RIBs over a variable velocity profile and provide an unrivalled longitudinal acceptance when coupled with solenoid focusing. The incorporation of the solenoids into the cryomodule shortens the linac, whilst maximising the acceptance, but the application of solenoid focusing in the presence of asymmetric QWR fields can have consequences for the beam quality. The rotation of an asymmetric beam produces an effective emittance growth in the laboratory reference system. We present modifications of the cavity geometry to optimise the symmetry of the transverse fields in the high-beta QWR. A racetrack shaped beam port is analysed and a modification made to the inner conductor with a geometry that will enable a niobium film to be effectively sputtered onto the cavity surface.
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