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Kii, T.

Paper Title Page
WEPPH023 Beam Properties from S-band Energy Compensated Thermionic RF Gun and Linac for KU-FEL 386
 
  • K. Masuda, H. Ohgaki, S. Sasaki, T. Shiiyama, H. Zen, T. Kii
    Kyoto IAE, Kyoto
 
  Energy degradation arising from back-bombardment effect was quite serious problem for using a thermionic RF gun as injector of FEL device. Thus we have developed energy compensation technique, which keeps cavity voltage as constant by controlling input RF power to the RF gun. We have successfully extracted electron beam with constant energy from the thermionic RF gun with the energy compensation technique*. However, PFN tuning of the Klystron modulator and time-varying beamloading would affect macro-pulse properties; energy spread, emittance, phase mismatch between RF gun and accelerator, etc. Thus we have estimated effects to the beam properties by using the 1D thermal conduction model** and PARMERA, and also evaluated these properties experimentally. The estimated and measured results were not so serious for KU-FEL system. We will discuss the comparison between the experimental results and the calculation results in this conference.

* N. Okawachi, et al., Proc. of the FEL 2006, pp.664-667 (2006)** T. Kii, et al., Nucl. Instr. and Meth. A 483 310-314 (2002)

 
WEPPH024 Numerical Evaluation of Oscillator FEL with Multi-Bunch Photo-Cathode RF-gun in Kyoto University 390
 
  • Y. Kamiya, M. Washio
    RISE, Tokyo
  • T. Kii, K. Masuda, S. Sasaki, T. Shiiyama, H. Zen, H. Ohgaki
    Kyoto IAE, Kyoto
  • M. Kuriki, N. Terunuma, J. Urakawa
    KEK, Ibaraki
  • R. Kuroda
    AIST, Tsukuba, Ibaraki
 
  An infrared FEL (4-13 micro-m) facility to develop new energy materials is constructed in Institute of Advanced Energy, Kyoto University. The electron beam of 40 MeV has been successfully accelerated by a linac system which consists of a 4.5-cell thermionic RF gun*. However, due to severe back-bombardment effect, there still needs several efforts to extend the macro-pulse duration to obtain a stable FEL. Upgrade from the present thermionic RF gun to a photocathode RF gun has been planned in KU-FEL**, because a photocathode RF gun is free from the back-bombardment and can generate a high brightness electron beam. A multi-bunch photo-cathode RF gun system has been developed*** and will be installed into the KU-FEL linac. Thus a design work on the new linac system from the gun to the FEL has been performed by using PARMELA and GENESIS. The evaluated peak current is about 4 times and the expected FEL gain is about 10 times as high as those with the present system. The required laser system will be discussed in this conference, as well.

* H. Ohgaki, et al., NIM A, vol.528, pp.366-370 (2004).** H. Ohgaki, et al., Proc. of the FEL 2004, pp.454-457 (2004).*** K. Hirano, et al., NIM A, vol. 560, pp.233-239 (2006).

 
WEPPH025 Progress in the FEL Lasing in Kyoto University 394
 
  • T. Kii, K. Masuda, H. Ohgaki, T. Shiiyama, H. Zen, S. Sasaki
    Kyoto IAE, Kyoto
 
  We have constructed an infrared (4~13μm) FEL facility for advanced energy researches in Kyoto University. The numerical studies on the expected FEL gain, which was based on the experimental measurements both of the undulator and of the electron beam parameters, were carried out*. However, g-parameter of the mirror cavity was located close to the unstable region. In order to obtain a stable FEL, we calculated the FEL gain taking into account the duct shape, the tilt angle, and the offset of the mirror, then for the first lasing the mirror parameter was optimized. At the present stage, we have installed the undulator and the mirror cavity. A spectrum of the spontaneous emission was measured, which was consistent with the result of spectrum calculation obtained with measured magnetic field of the undulator. In this conference, we will present the result of the mirror optimization, and measurement of the spontaneous emission. The status of the experiment on FEL lasing will also be addressed.

* M. Nakano, et al., Proceedings of the 2006 FEL conference, (2006)

 
WEPPH026 Design Study of the Triode-Type Thermionic RF Gun 398
 
  • K. Kanno, E. Tanabe
    AET Japan, Inc., Kawasaki-City
  • T. Kii, K. Masuda, H. Ohgaki, S. Sasaki, H. Zen, T. Shiiyama
    Kyoto IAE, Kyoto
 
  We use a 4.5-cell RF gun with a thermionic cathode as the injector for our KU-FEL facility, having taken its advantageous features compared with photocathode guns, such as high averaged current, low cost and easy operation, while we suffer from the limited macro-pulse duration and peak current by the back-bombardment effect. To mitigate these adverse effects, we proposed the triode-type thermionic RF gun with an additional small cavity providing the accelerating phase nearby the cathode independent of the main cavity phase*. Results from PIC simulations show that the back-bombardment power can be reduced drastically by more than 80%, and in addition the peak current of the output electron beam will be improved greatly by supplying a moderate RF power of tens kW to the RF triode structure. The RF system of up to 100 kW capabilities has been prepared and tested. Also the prototype design of the triode-type thermionic RF gun was completed. The cavity parameters, namely the quality factor, shunt impedance, and the coupling coefficient with the RF feed coaxial cable were designed taking into account both the available maximum field on the cathode and the phase and amplitude stability against the expected variations of the beam loading and cavity temperature. We will also present PIC simulation prediction on the output beam characteristics promising the first FEL lasing.

* K. Masuda, et al., Proceedings of the 2006 FEL conference, (2006)

 
WEPPH027 Beam Diagnostics for the First Lasing of the KU-FEL 402
 
  • T. Kii, K. Masuda, H. Ohgaki, S. Sasaki, T. Shiiyama, H. Zen
    Kyoto IAE, Kyoto
 
  Mid-IR FEL (4-13μm) device for energy science has been constructed in Institute of Advanced Energy, Kyoto University and the electron beam of 40MeV has been successfully accelerated*. The transverse phase space distribution and the corresponding emittance of the electron beam were measured by using a tomographic method**. As the result, normalized emittance was around 3 pi mm mrad. An FEL gain calculation*** shows that the peak current of 10A is the minimum value for the FEL amplification, and that of 40A is required to achieve the FEL saturation. Therefore the bunch compression experiment has been carried out to shorten the micro-bunch length by 2 ps in KU-FEL. The 180 deg. arc section was used for the bunch compression. We will report the result of the emittance measurement and of the bunch compression experiment in the conference.

* H. Ohgaki, et al., NIM A, vol.528, pp.366-370 (2004).** H. Zen, et al., Proc. of the FEL 2006, pp.592-595(2006)*** M. Nakano, et al., Proc. of the FEL 2006, pp.660-664 (2006).