Design method of bandwidth limiting neutron chopper system in CSNS

[Background] Bandwidth-limited neutron chopper (BWL choppers) is one of the indispensable key equipments in the time-of-flight neutron scatter of China spallation neutron source (CSNS), which decide the neutron energy spectrum obtained by detectors. The main principle is to chop the neutron beam to limit the neutron wavelength bandwidth at the neutron detector, so as to reduce the background and improve the signal-to-noise ratio. [Purpose] This study aims to design BWL chopper system reasonably and reduce faults. [Methods] The basis principle of BWL chopper was reviewed, Design method, basis configuration principle of BWL chopper and system layout were put forward. The formulas for calculating the physical parameters of BWL chopper were given. [Results] The configuration numbers of bandwidth chopper should meet the requirement of neutron scatter. The background removing chopper should be inserted in the front end of the beam line so that the neutrons in the required band of the spectrometer could pass through without loss, while the bandwidth selecting chopper should be placed at the back end as far as possible. In addition, the flux can be increased by double disk chopper that satisfies same phase, same speed, same slit angle but counter-rotating. [Conclusion] The work can guide the physical design of twenty neutron instruments of CSNS. (authors)