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Otono, H.

Paper Title Page
MOP079 Development of Modulating Permanent Magnet Sextupole Lens for Focusing of Pulsed Cold Neutrons 263
 
  • M. Yamada, H. Fujisawa, M. Ichikawa, Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto
  • P. Geltenbort
    ILL, Grenoble
  • K. Hirota, Y. Otake, H. Sato
    RIKEN, Wako, Saitama
  • T. Ino, K. Mishima, T. Morishima, S. Mutou, H.M. Shimizu, K. Taketani
    KEK, Tsukuba
  • Y. Kamiya, S. Kawasaki, S. Komamiya, H. Otono, S. Yamashita
    University of Tokyo, Tokyo
  • T. Oku, K. Sakai, T. Shinohara, J. Suzuki
    JAEA, Ibaraki-ken
  • Y. Seki
    Kyoto University, Kyoto
  • T. Yoshioka
    ICEPP, Tokyo
 
 

We are developing a modulating permanent magnet sextupole lens to focus pulsed cold neutrons. It is based on the extended Halbach configuration to generate stronger magnetic field. In order to adjust the strength, the magnet is divided into two nested co-axial rings, where the inner ring is fixed and the outer ring can be rotated. Synchronizing the modulation with neutron beam pulse suppresses the chromatic aberration. These devices largely improve the utilization efficiency of neutrons, which makes even small linac based neutron sources practical. We have fabricated a half-scale model and studied its strength, torque and temperature rise during the operation. The main causes of the temperature rise are eddy-current loss in the poles made of soft magnetic material in inner ring and hysteresis loss. A laminated structure reduced the eddy-current loss. The temperature rise was suppressed to about half of the former model. We now study their B-H curve to optimize the thickness of the sheet. Annealing of the material is supposed to reduce the hysteresis loss, which will be tested soon. The experimental results of very-cold neutrons focusing with the half-scale model are also described.

 

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