Billinghurst B E, Bergstrom J C, Baribeau C, Batten T, Dallin L, May T E, Vogt J M, Wurtz W A, Warnock R, Bizzozero D A, Kramer S
Canadian Light Source Inc., University of Saskatchewan, Saskatoon, Saskatchewan S7N 2V3, Canada.
SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, USA and Department of Mathematics and Statistics, University of New Mexico, Albuquerque, New Mexico 87131, USA.
Phys Rev Lett. 2015 May 22;114(20):204801. doi: 10.1103/PhysRevLett.114.204801. Epub 2015 May 20.
We report on high resolution measurements of resonances in the spectrum of coherent synchrotron radiation (CSR) at the Canadian Light Source (CLS). The resonances permeate the spectrum at wave number intervals of 0.074 cm(-1), and are highly stable under changes in the machine setup (energy, bucket filling pattern, CSR in bursting or continuous mode). Analogous resonances were predicted long ago in an idealized theory as eigenmodes of a smooth toroidal vacuum chamber driven by a bunched beam moving on a circular orbit. A corollary of peaks in the spectrum is the presence of pulses in the wakefield of the bunch at well-defined spatial intervals. Through experiments and further calculations we elucidate the resonance and wakefield mechanisms in the CLS vacuum chamber, which has a fluted form much different from a smooth torus. The wakefield is observed directly in the 30-110 GHz range by rf diodes, and indirectly by an interferometer in the THz range. The wake pulse sequence found by diodes is less regular than in the toroidal model, and depends on the point of observation, but is accounted for in a simulation of fields in the fluted chamber. Attention is paid to polarization of the observed fields, and possible coherence of fields produced in adjacent bending magnets. Low frequency wakefield production appears to be mainly local in a single bend, but multibend effects cannot be excluded entirely, and could play a role in high frequency resonances. New simulation techniques have been developed, which should be invaluable in further work.
我们报告了在加拿大光源（CLS）对相干同步辐射（CSR）光谱中共振的高分辨率测量结果。这些共振以0.074 cm⁻¹的波数间隔贯穿整个光谱，并且在机器设置（能量、束团填充模式、突发或连续模式下的CSR）变化时高度稳定。类似的共振早在一个理想化理论中就被预测为在圆形轨道上运动的束团驱动的光滑环形真空室的本征模。光谱中峰值的一个推论是在束团尾场中以明确的空间间隔存在脉冲。通过实验和进一步计算，我们阐明了CLS真空室中的共振和尾场机制，该真空室具有与光滑环面大不相同的槽形。通过射频二极管在30 - 110 GHz范围内直接观测尾场，并通过太赫兹范围内的干涉仪间接观测。二极管发现的尾脉冲序列比环形模型中的要不规则，并且取决于观测点，但在槽形室中的场模拟中得到了解释。关注观测场的极化以及相邻弯曲磁铁中产生的场的可能相干性。低频尾场产生似乎主要局限于单个弯曲处，但多弯曲效应不能完全排除，并且可能在高频共振中起作用。已经开发了新的模拟技术，这在进一步的工作中应该是非常有价值的。
