A group of researchers from CSNS recently finished a beam chopping test of the Fermi neutron chopper prototype. The chopper worked accurately producing several expected monochromatic energy neutron beams, marking its successful development as China’s first Fermi neutron chopper prototype.

The Fermi neutron chopper is used to select monochromatic energy neutron beams at 10~1500 meV of neutron energy and is a decisive factor in the instrument’s energy resolution and count rate, thus making it a key piece of equipment for time-of-flight inelastic neutron scattering instruments. The CSNS neutron chopper group overcame many technological difficulties, such as those related to the reliability of the rotor structure, dynamic balance and mechanical vibration, the reliability of the slit package’s neutron absorption coating, and high-precision synchronous motion control. Meanwhile, how to deal with the 600 Hz ultra-high mechanical speed (200 m/s linear velocity) was also one of the group’s greatest challenges. 

With the successful development of the prototype, CSNS will manufacture a Fermi neutron chopper for the high-energy, direct-geometry, inelastic neutron scattering instrument this year.

Time-of-flight neutron spectrum output from the Fermi chopper prototype