Abstract
The $X$-band choke-mode structure is currently being studied as an alternative design for the accelerating structure of the compact linear collider (CLIC) main linac. The geometry of the choke-mode structure is designed to ensure the strong suppression of the beam-induced long-range transverse wakefield and therefore maintain the stability and quality of the beam in the CLIC main linac. Experiments conducted at the Argonne Wakefield Accelerator Facility are presented in this study to verify the design of the wakefield suppressor. The beam-induced radio frequency (rf) signals in a three-cell choke-mode structure were measured, and measured results show good agreement with the simulation results. The measured results also show strong damping in high-order dipolar modes with a quality factor $Q$ of 10 to 20. The difference between the frequencies of the first and second dipole modes is about 3 GHz, which validates the special design of the cancelling dipole modes at the time of the succeeding bunch (0.5 ns).
Highlights
As the dimensions of accelerating structures become smaller or beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis
The X-band choke-mode structure is currently being studied as an alternative design for the accelerating structure of the compact linear collider (CLIC) main linac
The X-band choke-mode structure is currently being studied as an alternative design for the accelerating structure of the compact linear collider (CLIC) main linac [11,12]
Summary
As the dimensions of accelerating structures become smaller or beam intensities higher, the transverse wakefields driven by the beam become quite large with even a slight misalignment of the beam from the geometric axis. Electron and positron beams are accelerated to the energy of 1.5 TeV in two identical 21-km-long linacs which are mainly composed of high gradient normal conducting X-band structures. Such a long, high frequency band accelerating structure results in strong long-range transverse wakefield induced by the beams, which may cause multibunch instability. Aside from the choke-mode structure, there are other kinds of heavily damped structures, such as the waveguide damped structure and iris slotted damped structure [20] These structure designs have drawn much interest in the study of high-gradient normal conducting accelerating structures. Only one beam line was available at the time of this experiment.)
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