Author: Taira, Y.
Paper Title Page
MIR-FEL Oscillator Lasing by Photocathode Operation of LaB6 Thermionic Cathode in KU-FEL  
  • H. Zen, T. Kii, K. Masuda, H. Ohgaki, S. Suphakul
    Kyoto University, Kyoto, Japan
  • R. Kuroda, Y. Taira
    AIST, Tsukuba, Ibaraki, Japan
  Kyoto University Free Electron Laser (KU-FEL) is an oscillator type mid-infrared FEL having the tunable wavelength range from 5 to 22 micro-m [1]. The first lasing and power saturation of the facility using a 4.5-cell RF gun with a LaB6 thermionic cathode has been achieved in 2008 by overcoming the severe back-bombardment effect in the RF gun [2,3]. For upgrading the FEL performance, a multi-bunch picosecond mode-locked laser has been developed for driving a photocathode in the RF gun [4]. In February 2015, we have achieved first lasing of KU-FEL with photocathode operation of the LaB6 cathode in the 4.5-cell RF gun. The micro-pulse energy of the FEL at the wavelength of 11.7 micro-m with the photocathode operation was around 6.5 times as high as that with the thermionic cathode operation without any other modification of the FEL system. The performance of KU-FEL in the photocathode operation mode and comparison with the thermionic cathode operation will be presented in the conference.
[1] H. Zen, et al., Proc. of FEL2013, p.711, 2013
[2] H. Ohgaki, et al., JJAP, 47, p.8091, 2008
[3] H. Ohgaki, et al., Proc. of FEL08, p.4, 2008
[4] H. Zen, et al., Proc. of FEL2014, p.828, 2015
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TUD02 Diffraction Radiation Monitor 561
  • Y. Taira
    AIST, Tsukuba, Japan
  Non-invasive beam diagnostics using a diffraction radiation (DR) has been developed at several electron accelerator facilities. Generation process of DR is similar to that of transition radiation (TR). TR is emitted when a charged particle passes through the boundary between two media with different dielectric constants. On the other hand, DR is emitted when it passes through in the vicinity of a boundary between two media. In the generation process of DR, the charged particle doesn't intersect the medium but its electric field intersects the medium. An aperture, a slit, and an edge are used for DR target. Optical wavelength of DR is usually used for beam diagnostics. One can evaluate energy, a transverse beam size, and a divergence of an electron beam by measuring a spatial distribution of DR. Moreover, coherent diffraction radiation with the wavelength of less than millimeter range is used for a bunch length measurement. In this conference, a theoretical background of DR and experimental results carried out at several facilities will be presented.  
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