High-efficiency improvement for high energy resolution experimental mode of DIANA spectrometer at Materials and Life Science Facility (MLF) of J-PARC

Takahashi, Nobuaki; Shibata, Kaoru  ; Sato, Taku*; Arai, Masatoshi

DIANA is an indirect-geometry time-of-flight spectrometer which is planed to install at MLF, J-PARC. It has three exchangeable analyzer crystals, such as PG(002), Ge(311) and Si(111) for different energy transfer, momentum transfer, energy resolution experiments. Normal experimental mode, either PG(002) or Ge(311) analyzer is used, shows moderate energy resolutions of 15 micro eV or 40 micro eV, respectively. We are especially aiming very high energy resolution of 2 micro eV by using Si(111) analyzer crystal together with high speed counter-rotating pulse-shaping choppers with each rotation frequency of 300 Hz as an optional setting for the spectrometer. Although such a high energy resolution is attained, it is considerably inefficient having a very narrow incident energy (Ei) band if the pulse shaping chopper has only one slit. Therefore, we have designed multi-slit chopper and have performed Monte-Carlo simulation to study Repetition Rate Multiplication (RRM) capability.