Physical design and performance research of two counter-rotating T0 choppers for the multi-physics neutron diffractometer at China Spallation Neutron Source

Abstract

The T0 chopper has the ability to remove the fast neutrons and high-energy gamma rays emitted at time zero of each pulse cycle. The multi-physics instrument of the China Spallation Neutron Source requires high epithermal neutron flux to obtain large momentum transfer, and the traditional single T0 chopper is a disadvantage for the transmission of epithermal neutrons in the long focusing guide. To solve this problem, the two counter-rotating T0 chopper design is proposed that can greatly improve the transmission efficiency of epithermal neutrons. The results of the beam experiment show that compared with the single T0 chopper operating at 50 Hz, the two counter-rotating T0 choppers at the same speed significantly improves the transmission efficiency of epithermal neutrons (especially the shorter wavelength neutrons). For example, when the two blades partially overlap, the transmission efficiencies of 0.05 Å, 0.1 Å, and 0.2 Å wavelength neutrons are increased by 9.4, 4.7, and 4.6 times, respectively, which fully proves that the two counter-rotating T0 chopper design is reasonable, and the experimental results are in line with expectations. The design and application of two counter-rotating T0 choppers at the China Spallation Neutron Source is the first example of this in the world and can be applied to neutron spectrometers with high epithermal neutron flux requirements, and can also be extended to fields such as the energy selection of high-energy particles.