• H. Hama, F. Hinode, M. Kawai, T. Tanaka
  LNS, Sendai

Funding: Supported partly by a Grant-in Aid for Scientific Research from Japan Society for the Promotion of Science, #17360035

As a result of simulation study so far, a specific feature has been found in the longitudinal dynamics in thermionic RF guns. At the beginning of beam extraction, the head of the electrons from a cathode is followed immediately by the electrons just behind, which is extracted by the higher electric field than that at the head of the beam train. Thus later electrons would get velocity faster than the head of the electrons, so that the electrons are expected to concentrates onto the head of the beam under certain conditions such as the gun geometry and the strength of the RF field. In order to investigate this velocity-bunching like effect, a prototype thermionic RF gun was designed and its characteristics have been studied by a 3-D simulation code based on a FDTD (finite difference time demain) method. The gun is consists of two independentlly power feeding S-band RF cavities, and can be operated at modes with different power ratio and phase between two RFs. This paper report the thermionic RF gun is expected to produce several hundreds femtosecond pulse containing approximately 0.1 nC, which may be a powerful tool to generate THz coherent radiation or FELs driver.

• T. Tanaka
  RIKEN Spring-8, Hyogo
• Y. Asano
  JAEA, Ibaraki-ken
• H. Baba, T. Bizen, Z. Chao, H. Ego, S. Eguchi, S. Goto, T. Inagaki, S. Inoue, D. Iwaki, K. Kase, Y. Kawashima, H. Kimura, S. Kojima, T. Kudo, N. Kumagai, X. Marechal, S. Matsui, T. Ohata, K. Onoe, Y. Otake, T. Seike, K. Shirasawa, N. Shusuke, T. Takagi, T. Takashima, K. Tamasaku, R. Tanaka, K. Togawa, R. Tsuru, S. Wu, M. Yabashi, S. Yoshihiro
  JASRI/SPring-8, Hyogo
• T. Fukui
  Kyoto IAE, Kyoto
• T. Hara, T. Ishikawa, H. Kitamura, T. Shintake
  RIKEN Spring-8 Harima, Hyogo
• H. Matsumoto
  KEK, Ibaraki
• S. Takahashi
  LNS, Sendai

Funding: Representing the SCSS project team

SCSS, an acronym of "SPring-8 Compact SASE Source", is an X-ray FEL project under planning to be build at the SPring-8 site. R&Ds for accelerator components such as the pulsed-DC electron gun, C-band main linac, and in-vacuum short period undulator have been performed and almost completed. Before construction of the X-ray FEL facility, a prototype accelerator with the electron energy of 250 MeV is being built to demonstrate the concept of SCSS. In this presentation, status of the R&Ds for each accelerator component will be presented together with an overview of the 250-Mev prototype accelerator.

• K. Hayakawa, Y. Hayakawa, K. Nakao, K. Nogami, T. Sakai, I. Sato, T. Tanaka
  LEBRA, Funabashi

Funding: "Academic Frontier" Project for Private Universities: matching fund subsidy from MEXT (Ministry of Educatin, Culture, Sports, Science and Technology), 2000-2004

In general, maximum gain and maximum power of a free-electron laser (FEL) oscillator are not simultaneously satisfied at an identical length of the optical resonator. Use of a short bunch electron beam, therefore, can cause a large fluctuation of gain and saturated power of the FEL due to only a small change in the resonator length. If the length of the resonator can be adjusted at the middle in the macropulse duration of the electron beam, both maximizing conditions will be satisfied simultaneously, which will result in a large FEL output power compared with a normal operation. Since it is difficult to change the length of the resonator during the macro pulse, modulation of the bunch interval has been attempted for the LEBRA FEL system by modulating the phase of the accelerating rf of the electron linac, which has an equivalent effect to change of the resonator length. The modulation of the rf phase has resulted in intensification of the output energy per macro pulse by approximately twice compared with that in normal operation, which is consistent with numerical simulation.

• T. Tanaka
  RIKEN Spring-8, Hyogo
• T. Bizen, D. Iwaki, X. Marechal, T. Seike, R. Tsuru
  JASRI/SPring-8, Hyogo
• T. Hara, H. Kitamura
  RIKEN Spring-8 Harima, Hyogo

In-vacuum undulators are now widely used in lots of SR facilities to provide highly-brilliant hard x-rays not only in large-scale facilities such as SPring-8, ESRF and APS, but also in medium-scale facilities with an electron energy up to 3 GeV. In addition, the SCSS (SPring-8 Compact SASE Source) project is going to adopt the in-vacuum undulator not only for reducing the electron energy to achieve angstrom X-ray FEL but also for commissioning and alignment of components in the undulator line that takes advantage of variable vacuum gap (physical aperture for the electron beam). In this talk, overview of technologies required for development of the in-vacuum undulator will be presented together with practical examples. In addition, ongoing R&Ds at SPring-8 (cryogenic undulator, in-situ field measurement system) will be described in brief.