Design of the Wien-filter type spin rotator for the low-emittance muon beam

Yasuda, Hiromasa*; Iinuma, Hiromi*; Nakazawa, Yuga*; Saito, Naohito; Kawamura, Naritoshi*; Otani, Masashi*; Mibe, Tsutomu*; Kondo, Yasuhiro   ; Sue, Yuki*

Muon linac is developed for the muon g-2/EDM experiment at J-PARC. In this experiment, ultra slow muon is accelerated to a momentum of 300 MeV/c with the four linac structures. This scheme offers new opportunity for precise measurements; it enables us to reverse muon polarization at early stage of acceleration. The reversal of polarization is a common method of precision polarization measurements as it can be used to identify or reduce systematic uncertainties dependent on time. It is necessary to accelerate muons and flip its spin without substantial emittance growth for the experimental requirement. As one of the candidates for our spin rotator, we are developing the Wien-filter type. The emittance growth is +64% in x-x' plane and +56% in y-y' plane, but it is revealed it would be reduced by tuning electric field to + 47% in x-x' plane and + 2% in y-y' plane. In this paper, the design of the Wien-filter type spin rotator for the low emittance muon beam will be presented.