High-gradient two-beam accelerator structure
High-gradient two-beam accelerator structure
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高梯度双光束加速器结构
DOI：
10.1103/physrevstab.13.071303
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发表时间：
2010
影响因子：
--
通讯作者：
J. Hirshfield
中科院分区：
文献类型：
--
作者：
S. Kazakov;S. Kuzikov;Yong Jiang;J. Hirshfield
提出了一种新的加速结构，其目标是为下一代多TeV直线对撞机提供150 mV/m的梯度[1-3]。这种结构是基于周期系统的准光学腔，它们彼此不耦合。这些腔中的每一个都被空间聚束驱动光束以几个等距离间隔的本征模激励，使得射频场仅在加速束团驻留在腔中的短时间间隔内达到峰值，从而使腔表面仅在一小部分时间内暴露在最强场中。这一功能有望提高击穿和脉冲加热阈值。与通常的单频加速结构相比，该结构的最大表面场与加速梯度的比值α较小(1<；α<；2)，接近因子2。由于新加速结构的所有腔体都是非耦合的，所以结构非常可靠，即可能在单独的腔体中击穿不会损坏整个加速器。通过所谓的频率失谐概念，有望提供驱动束功率和加速束功率的高效率和变换比。根据这一思想，大电流驱动束以分布的方式(沿加速器远距离)输出能量。这是由于结构腔的本征频率在驱动束团频率之外失谐而实现的。对一种由多模平行驱动矩形腔和加速束流组成的新型双光束加速结构的计算表明，在接近CLIC(CERN)的束流参数下，可以获得高梯度(~150 mV/m)、低表面场(~190 mV/m)和高效率(~30%)的束流参数。这种结构体现了大多数其他吸引人的特性：腔体是一种全金属结构，驱动通道和加速通道之间不需要传输或耦合结构，腔场围绕驱动光束和加速光束的轴对称。
A new accelerating structure, which is aimed to provide gradient >150 MV/m for next generation of multi-TeV linear colliders, is suggested [1-3]. The structure is based on periodic system of quasi-optical cavities, which are not coupled with each other. Each of these cavities is excited in several equidistantly-spaced eigen modes by the spatially bunched drive beam in such a way that the RF fields reach peak values only during the short time intervals when an accelerating bunch is resident in a cavity, thus exposing the cavity surfaces to strongest fields for only a small fraction of time. This feature is expected to raise the breakdown and pulse heating thresholds. The proposed structure has smaller ratio α of maximal surface field to accelerating gradient (1<α<2) in comparison with usual single-frequency structure, where this ratio is close to factor 2. Due to all cavities of new accelerating structure are uncoupled, the structure is very reliable, i.e. possible breakdown in a separate cavity does not spoil the whole accelerator. High efficiency and transformer ratio of drive beam power to accelerating beam power are expected to be provided by means of a so-called idea of frequency detuning. In accordance with this idea high-current drive beam leaves its power in a distributed way (at long distance along accelerator). This is achievable due to detuning of eigen frequencies of a structure cavity out of drive bunch frequency. Calculations of a new two-beam accelerating structure consisted of multi-mode rectangular cavities with the parallel driving and accelerated beams, show that high gradient (~150 MV/m), low surface field (~190 MV/m), and high efficiency (~30%) are achievable under beam parameters close to those projected for CLIC (CERN). This structure embodies most of additional attractive properties: the cavity is an all metallic structure, no transfer or coupling structures are needed between the drive and acceleration channels, the cavity fields are symmetric around the axes of the drive beam and the accelerated beam.