Upgraded Fermi chopper of the chopper spectrometer 4SEASONS at J-PARC

Nakamura, Mitsutaka   ; Kajimoto, Ryoichi  ; Inamura, Yasuhiro  ; Aoyama, Kazuhiro; Kambara, Wataru*; Kawakami, Kazuhiro; Kubo, Naoya; Kamazawa, Kazuya*; Ikeuchi, Kazuhiko*; Iida, Kazuki*; Ishikado, Motoyuki*

The chopper spectrometer 4SEASONS at J-PARC MLF had used a Fermi chopper borrowed from the SNS facility until 2014. A new Fermi chopper which reviewed the design of the slit package has recently started operation. As a result, we have succeeded in achieving the intensity gain up of to several tens of times in the low-energy region. In this presentation we will report the details of spec and design of a new Fermi chopper.