Author: Hotei, T.
Paper Title Page
TU1P03
Observation of Resonant Coherent Diffraction Radiation from a Multi-bunch Electron Beam Passing Through an Optical Cavity  
 
  • Y. Honda, A. Aryshev, R. Kato, T. Miyajima, T. Obina, M. Shimada, R. Takai, T. Uchiyama, N. Yamamoto
    KEK, Ibaraki, Japan
  • T. Hotei
    Sokendai, Ibaraki, Japan
 
  Funding: This work was supported by JSPS KAKENHI Grant Number 16H05991.
Energy Recovery Linac can realize a linac-type beam at a high current. An ERL test accelerator, cERL, has been constructed in KEK. Utilizing these features of the ERL beam, low emittance, short bunch, and high repetition rate, we have been developing a unique terahertz radiation source of resonant coherent diffraction radiation. An optical resonant cavity consists of two concave mirrors with a beam hole at the center was installed in the return-loop of cERL. When the multi-bunch electron beam passes through the cavity, it radiates coherent diffraction radiation in the cavity. If the round-trip time of the cavity precisely matches the beam repetition, the radiation of the bunches are stacked coherently and stimulates the energy conversion process from the beam to the radiation. Measuring the terahertz radiation power while scanning the cavity length, we observed a sharp resonance peak showing the realization of the stimulated emission. The cavity was carefully designed to tune the carrier-envelope-offset to be zero. It allows to excite wide-band longitudinal modes simultaneously, and realize a mode-locked terahertz pulse.
 
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THPO009 Evaluation of 60pC Beam Performance at cERL Injector for ERL Based EUV-FEL 699
SPWR001   use link to see paper's listing under its alternate paper code  
 
  • T. Hotei
    Sokendai, Ibaraki, Japan
  • R. Kato, T. Miyajima
    KEK, Ibaraki, Japan
 
  In order to compensate for the emittance which is increased by space charge in the low energy region, it is important to transport the beam as designed. Until now, we did not consider couplers in injector superdonducting cavities in optics design. But in this study, to improve optics matching and emittance compensation conditions for space charge dominated beam in cERL at KEK, we introduced a new 3D cavity model. We first investigated the influence of the couplers on electromagnetic field distribution. As a result, it was found that an asymmetric focusing force is generated by the influence of the couplers. It also became clear that the influence of the coupler kick on the optics significantly devastated the emittance compensation condition from the calculating including space charge. Furthermore, it was found that by optimizing the optics in consideration of the coupler kick, it is possible to improve the beam control accuracy and reduce the emittance in beam commissioning.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-LINAC2018-THPO009  
About • paper received ※ 12 September 2018      issue date ※ 18 January 2019  
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