Author: Ohgaki, H.
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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
slides icon Slides MOA01 [1.347 MB]  
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MOP025 Electron Beam Properties from a Compact Seeded Terahertz FEL Amplifier at Kyoto University 85
  • K. Damminsek, S. Rimjaem, S. Suphakul, C. Thongbai
    Chiang Mai University, Chiang Mai, Thailand
  • H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  A compact seeded Terahertz FEL amplifier is started construction at Institute of Advanced Energy, Kyoto University, Japan. The system consists of a 1.6 cell BNL type S-Band photocathode RF-gun, a magnetic bunch compressor in form of a chicane, triplet quadrupole magnets and a short planar undulator. Electron beams from the photocathode RF-gun were measured and compared with the PARMELA simulation results. Numerical and experimental studies on the contribution of the space charge effect were carried out. By using the RF power of 9 MW, the RF phase of 40 degree, the laser pulse energy of 20 μJ, and the solenoid magnet current of 135 A, the electron beam with a bunch charge of 50 pC, a beam energy of around 5 MeV and an RMS emittance of 6-8 mm-mrad was achieved.  
poster icon Poster MOP025 [1.837 MB]  
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MOP050 Development of Coherent Terahertz Wave Sources using LEBRA and KU-FEL S-band Linacs 143
  • N. Sei, H. Ogawa
    AIST, Tsukuba, Ibaraki, Japan
  • K. Hayakawa, Y. Hayakawa, M. Inagaki, K. Nakao, K. Nogami, T. Sakai, T. Tanaka
    LEBRA, Funabashi, Japan
  • H. Ohgaki, H. Zen
    Kyoto University, Kyoto, Japan
  Funding: This work is supported by the "ZE Research Program, IAE ZE27B-6".
In an infrared free-electron laser (FEL) facility using an S-band linac, a short-bunched electron beam is required to obtain a high FEL gain. Generally, the bunch length of the electron beam is compressed to 1 ps or less before interaction with the photons accumulated in the FEL resonator. This suggests that the electron beam dedicated to the FEL oscillation is suitable for generation of high-peak-power coherent radiation in terahertz (THz) wave region. Using the compressed electron beams, the coherent THz-wave sources have been developed at Laboratory for Electron Beam Research and Application (LEBRA) in Nihon University and Kyoto University Free Electron Laser (KU-FEL). The observed powers have been higher than 100 micro-joule per macropulse*. In this presentation, the properties of the high-power coherent THz waves generated at the bending magnets will be reported.
* N. Sei et al., J. Opt. Soc. Am. B 31 (2014) 2150.
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Image Charge Effect on Emittance Reduction Phenomenon in Electron Gun  
  • T. Nogi
    Kyoto Univeristy, Kyoto, Japan
  • T. Katsurayama, T. Kii, K. Masuda, K. Morita, T. Murata, K. Nagasaki, H. Ohgaki, S. Suphakul, K. Torgasin, H. Yamashita, H. Zen
    Kyoto University, Kyoto, Japan
  Development of next generation light sources requires reduction of beam emittance. The emittance can be influenced in the vicinity of a cathode, where electron energy is low and the beam dynamics is dominated by space charge and image charge effect. Recently it was discovered that for ideal DC acceleration emittance rises near cathode and subsequently decreases due to self-linearization force caused by space charge effect [*]. This phenomenon occurs for accelerating field, which is lower than usually applied at conventional electron guns. It is an issue that this concept is feasible for electron gun configuration of real injectors. In this research we numerically investigate the transverse emittance and its dependence on parameters such as current density, accelerating field and the distance from the cathode. As a result, the position of minimal emittance was found to be correlated to perveance. This position can be varied by proper settings of parameters. In this conference, we will present these phenomena seen numerically in the SCSS thermionic gun geometry.
* A. Mizuno, et al., Nucl. Instr. Meth. Phys. Res. A 774 (2015) 51-59.
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WEP010 Development of Phonon Dynamics Measurement System by MIR-FEL and Pico-second Laser 615
  • T. Murata, T. Katsurayama, T. Kii, T. Konstantin, K. Masuda, T. Nogi, H. Ohgaki, S. Suphakul, K. Torgasin, H. Zen
    Kyoto University, Kyoto, Japan
  • K. Hachiya
    Kyoto University Graduate School of Energy Science, Kyoto, Japan
  • K. Yoshida
    Kumamoto University, Department of Applied Chemistry and Biochemistry, Kumamoto, Japan
  Coherent control of a lattice vibration in bulk solid (mode-selective phonon excitation: MSPE) is one of the attractive methods in the solid state physics because it becomes a powerful tool for the study of ultrafast lattice dynamics (e.g. electron-phonon interaction and phonon-phonon interaction). Not only for that, MSPE can control electronic, magnetic, and structural phases of materials. In 2013, we have directly demonstrated MSPE of a bulk material with MIR-FEL (KU-FEL) by anti-Stokes Raman scattering spectroscopy. For the next step, we are starting a phonon dynamics measurement to investigate the difference of physical property between thermally excited phonon (phonon of equilibrium state) and optically excited phonon (phonon of non-equilibrium state) by time-resolved method in combination with a pico-second VIS laser. By using pico-second laser, we also expect to perform the anti-Stokes hyper-Raman scattering spectroscopy to extend MSPE method to the phonon mode which has Raman inactive . As the first step, we have commissioned the time-resolved phonon measurement system and started measurement on 6H-SiC. In this conference, we will present the outline of measurement system, and experimental results.  
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