Author: Miyajima, T.
Paper Title Page
MOIACC002 Development of SRF Gun Applying New Cathode Idea Using a Transparent Superconducting Layer 1
  • T. Konomi, Y. Honda, E. Kako, Y. Kobayashi, S. Michizono, T. Miyajima, K. Umemori, S. Yamaguchi, M. Yamamoto
    KEK, Ibaraki, Japan
  • R. Matsuda
    Mitsubishi Heavy Industries Ltd. (MHI), Takasago, Japan
  • T. Yanagisawa
    MHI-MS, Kobe, Japan
  KEK has been developing a superconducting RF gun for CW ERL since 2013. The SRF gun is a combination of a 1.3 GHz, 1.5-cell superconducting RF cavity and a backside excitation type photocathode. The photocathode consists of transparent substrate MgAl2O4, transparent superconductor LiTi2O4 and bi-alkali photocathode K2CsSb. The reason for using transparent superconductor is to reflect RF by using the feature of penetration depth of superconductor, which is defined from London equation. It protects optical components from RF damage. The critical DC magnetic field of the cathode, quantum efficiency and initial emittance were measured. These show the cathode can be used for the SRF gun. The gun cavity was designed to satisfy the photocathode operation. Eight vertical tests of the gun cavity have been performed. The surface peak electric field reaches to 75 MV/m with the dummy cathode rod which was made of bulk niobium.  
slides icon Slides MOIACC002 [2.185 MB]  
DOI • reference for this paper ※  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
Resonant Coherent Diffraction Radiation System at KEK-cERL  
  • Y. Honda, A. Aryshev, T. Miyajima, T. Obina, R. Ryukou, M. Shimada, R. Takai, N. Yamamoto
    KEK, Ibaraki, Japan
  Coherent radiation from a short bunched electron beam has been expected to be a high power source in THz regime. Especially the feature of the modern energy recovery linac is suitable for a high averaged power source. We propose to test an advanced scheme of resonantly exciting coherent diffraction radiation in an optical cavity. By stimulating the radiation in a multi-bunch beam, highly enhanced radiation power can be extracted. This system can excite all the cavity longitudinal modes at the same time, it can be a broadband source. We are preparing an experimental setup to test the resonant radiation in the cERL at KEK.  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
Identification of Ion Bombardment Area on the Photocathode After 900 μA CW Beam Operation at cERL  
  • M. Yamamoto, Y. Honda, X.J. Jin, T. Miyajima, T. Obina
    KEK, Ibaraki, Japan
  • Y. Kameta
    e-JAPAN IT Co. Ltd, Hitachi, Japan
  • T. Kawasaki
    Toshiba, Yokohama, Japan
  • N. Nishimori
    QST, Tokai, Japan
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  Compact-ERL (cERL) which is under development as an ERL demonstration machine at KEK succeeded in stable supply of CW beam exceeding 900 uA from a GaAs photocathode mounted on a DC-gun in March 2016. In the case of high current beam operation, the ions generated by collision of the beam and the residual molecules on the beam axis is increase and its flow back to the electron gun. As a result, the quantum efficiency (QE) of the photocathode decreases due to ion bombardment is the main factor of determining the cathode lifetime. After the CW operation of the accumulated extracted charge of ~10 Coulomb, steady decrease in QE due to ion bombardment has not yet been clearly confirmed. In order to analyze the area damaged by ion bombard, 2D QE distribution (QE map) measurement system was newly installed in the cathode preparation system. From QE map analysis before and after the CW operation, we confirmed two types of QE decrease. The area about 2 mm diameter near the center of the photocathode that the QE recovery is insufficient by the reactivation process is presumed the damage by ion bombardment.  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
Commission Results of the Compact ERL High Voltage DC Gun  
  • N. Nishimori
    Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
  • R. Hajima, R. Nagai
    QST, Tokai, Japan
  • Y. Honda, X.J. Jin, T. Miyajima, T. Obina, T. Uchiyama, M. Yamamoto
    KEK, Ibaraki, Japan
  • M. Kuriki
    HU/AdSM, Higashi-Hiroshima, Japan
  Funding: This work is partially supported by JSPS Grant-in-Aids for Scientific Research in Japan (15H03594, 16K05385).
Beam commissioning of the compact ERL (cERL) has been performed for the next generation ERL light sources such as a laser Compton gamma-ray source and a high power FEL for EUV lithography. The operational high voltage of the cERL DC gun has been limited to 390 kV due to failure of the ten segmented insulators. In November 2015, we installed an additional two segmented insulators on the top of the existing ten segmented insulators. In December 2015, we successfully performed high voltage conditioning up to 500 kV. We also found high voltage threshold for stable operation in a dc electron gun [1]. The cERL operational voltage has been 450 kV in maximum since then. We will present details of the high voltage upgrade and operational status at 450 kV of the cERL gun.
[1] Masahiro Yamamoto and Nobuyuki Nishimori, APL 109, 014103 (2016).
slides icon Slides WEICCC001 [6.787 MB]  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
Higher Bunch Charge Operation in Compact ERL at KEK  
  • T. Miyajima
    KEK, Ibaraki, Japan
  Abstract not submitted at print time.  
slides icon Slides THIACC001 [5.164 MB]  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
Beam Halo Study at the KEK Compact ERL  
  • O. Tanaka, T. Miyajima, N. Nakamura, M. Shimada
    KEK, Ibaraki, Japan
  • T. Hotei
    Sokendai, Ibaraki, Japan
  • K. Osaki
    Toshiba, Tokyo, Japan
  Funding: Work supported by the Grant-in-Aid for Creative Scientific Research of JSPS (KAKENHI 15K04747).
The beam halo control is of a great importance to attain high intensity beams. Thus, its detailed treatment is indispensable for the stable and safe operation. A systematic beam halo study was established at the KEK Compact ERL (cERL) since machine commissioning in spring 2015 in order to understand the beam halo formation and to have the stable and safe operation. The results of halo simulations have given a reasonable explanation of the low bunch charge (0.2-0.3 pC) beam profiles evaluated during the measurement. Thus, vertical beam halos observed at cERL are supposed to be due to the longitudinal bunch tails transferred into the transverse plane. Tails are mainly produced by the cathode response on the laser excitation. Further, when a beam passing the rf cavity off-center it experiences rf field kicks. The beam tilt could be a complex effect of the steering coils and cavities misalignments. During spring 2017 commissioning the bunch charge was increased up to 40 pC. In present study we are challenging to describe how the space charge effect acts on the beam halo profiles, and how the halo formation mechanisms change in this connection.
slides icon Slides THICCC001 [3.154 MB]  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)