Electromagnetic Design of a Superconducting Twin Axis Cavity
Electromagnetic Design of a Superconducting Twin Axis Cavity
复制标题
超导双轴腔的电磁设计
DOI：
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
HyeKyoung Park
中科院分区：
文献类型：
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作者：
S. Silva;J. Delayen;A. Hutton;F. Marhauser;HyeKyoung Park
双轴腔是一种新型的射频超导腔，它由两个平行的束管组成，可以在同一腔内对空间分离的两束束进行加减速。这种配置对具有低能电子的大电流束流特别有效，这些电子束将用于高能质子或离子的束流冷却。这种新的腔体结构利用TM110偶极子模式为两束产生均匀的加速或减速场。本文对目前正在研制中的1497 MHz双轴单腔体进行了射频优化设计。介绍利用两个束管的椭圆形射频超导加速结构用于能量回收直线加速器(ERL)的想法是由Noguchi和Kako在2003年首次提出的[1]。类似的概念在2007年[2，3]和最近[4]被Wang、Noonan和Lewellen重新提出，用于基于ERL的应用程序。新提出的超导双轴腔可以通过在两个束管中的同一个腔内加速和减速束流来回收能量。加速光束与平行加速/减速光束在物理上是分开的，但与相同的射频偶极子模式相互作用。例如，在ERL中，从源发射的低能量光束可以被注入到腔中，而不需要复杂的合并结构，从而不需要额外的光束线空间来弯曲光束，同时保持较小的光束发射度。图1：双轴空腔。如图1所示，这种新的双轴腔体结构旨在通过在TM110 RF偶极模式下工作来为两束光束创建一个均匀的场。两束管中的电磁场是轴对称的，相位偏移为180度。轴上电场和磁场在横截面上如图2所示。图2：双轴腔体横截面上的电场(左)和磁场(右)分布。对束管轴线位置进行了优化，以使轴上纵向电场分量(ez(Z))最大化，同时尽量使横向电场(Ex(Z)和Hy(Z))最小化。腔体形状的优化侧重于在不降低加速分量的情况下使横向分量最小化。请注意，与使用TM单极模式的传统加速腔不同，腔中心的磁场很强，其中峰值表面磁场在赤道。设计优化如图3(A)所示，双轴腔体的最初设计是一个圆柱形的几何形状，然后演变成一个带有压缩中段的跑道形状的设计。对设计进行了改进，以改善射频性能，主要是为了减少峰值表面磁场。
The twin-axis cavity is a new kind of rf superconducting cavity that consists of two parallel beam pipes, which can accelerate or decelerate two spatially separated beams in the same cavity. This configuration is particularly effective for high-current beams with low-energy electrons that will be used for bunched beam cooling of high-energy protons or ions. The new cavity geometry was designed to create a uniform accelerating or decelerating fields for both beams by utilizing a TM110 dipole mode. This paper presents the design rf optimization of a 1497 MHz twin-axis single-cell cavity, which is currently under fabrication. INTRODUCTION The idea of utilizing elliptical shaped rf superconducting accelerating structures with two beam pipes intended for Energy Recovery Linacs (ERLs) applications was first proposed by Noguchi and Kako in 2003 [1]. A similar concept was revisited by Wang, Noonan, and Lewellen in 2007 [2, 3] and recently [4] for based ERL applications. The new proposed superconducting twin-axis cavity allows energy recovery by accelerating and decelerating beams within the same cavity in two beam pipes. The accelerated beam is physically separated from the parallel accelerated/decelerated beam, but interacts with the same rf dipole mode. In an ERL for instance, the low energy beam delivered from the source can be injected into the cavity without requiring a complicated merger structure and thus additional beam line space to bend the beam, while maintaining a small beam emittance. Figure 1: Twin axis cavity. The new twin-axis cavity geometry, shown in Fig. 1, is designed to create a uniform field for both beams by operating in the TM110 rf dipole mode. The electromagnetic fields in the two beam pipes are axially symmetric with a 180 degree phase offset. The on-axis electric field and magnetic field at the cross sectional planes are shown in Fig 2. Figure 2: Electric (left) on-axis and magnetic (right) field profile at the cross section of the twin axis cavity. The beam pipe axis position has been optimized to maximize the on-axis longitudinal electric field component (Ez(z)) trying to symmetrize the field across the beam aperture as best as possible, while minimizing the transverse fields (Ex(z) and Hy(z)). The optimization of the cavity shape focused on minimizing the transverse component without degrading the accelerating component. Note that the magnetic field is strong at the center of the cavity unlike in conventional accelerating cavities using a TM monopole mode, where the peak surface magnetic field is at the equator. DESIGN OPTIMIZATION The initial design of the twin axis cavity was a cylindrical shaped geometry as shown in Fig. 3(a), which then evolved into a racetrack-shaped design with a compressed mid-section. The design has been modified to improve the rf properties, primarily to reduce the peak surface magnetic field.