Abstract
We observed multiple-collision free-electron laser (FEL)-Compton backscattering in which a multi-bunch electron beam makes head-on collisions with multi-pulse FELs in an optical cavity, using an infrared FEL system in the storage ring NIJI-IV. It was demonstrated that the measured spectrum of the multiple-collision FEL-Compton backscattering gamma rays was the summation of the spectra of the gamma rays generated at each collision point. Moreover, it was demonstrated that the spatial distribution of the multiple-collision FEL-Compton backscattering gamma rays was the summation of those of the gamma rays generated at each collision point. Our experimental results proved quantitatively that the multiple collisions in the FEL-Compton backscattering process are effective in increasing the yield of the gamma rays. By applying the multiple-collision FEL-Compton backscattering to high-repetition FEL devices such as energy recovery linac FELs, an unprecedented high-yield gamma-ray source with quasi-monochromaticity and wavelength tunability will be realized.
Highlights
Backward Compton scattering, which is inelastic scattering between a photon and a relativistic electron, can generate a high-energy photon [1]
In order to clarify the characteristics of the multiple-collision free-electron laser (FEL)-Compton backscattering gamma rays, the spectra of the gamma rays generated at each collision point were individually measured during the two-bunch operation
By controlling the interval between an electron bunch and an FEL pulse in the optical cavity in asymmetric two-bunch operation, the spectra of the FEL-Compton backscattering gamma rays generated at each collision point were measured
Summary
Backward Compton scattering, which is inelastic scattering between a photon and a relativistic electron, can generate a high-energy photon [1]. Backward Compton scattering is recognized as a factor that causes a spectral shift of the cosmic microwave background [2] In actuality, it has been experimentally demonstrated using coherent synchrotron radiation and transition radiation that backward Compton scattering causes wavelength conversion to a broadband light beam [3,4]. A practical application of backward Compton scattering is to obtain quasi-monochromatic X-ray and gamma-ray beams using an intense laser as the incident light. This laser Compton scattering (LCS) gives the best quasi-monochromatic X-ray and gamma-ray sources which have sufficient intensity and controllable polarization in the energy region over keV [5,6]. Laser performance has been dramatically improved, and studies using electron beams with high-intensity and short-pulse lasers in linear accelerators have been actively promoted [6,11,12,13]
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