Beam dynamics and commissioning of CW RFQ for a compact deuteron–beryllium neutron source

The Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) is building a compact neutron source using a superconducting linac. The injector RFQ will operate in continuous wave (CW) mode, accelerating a 10-mA deuteron beam from 20 keV/u to 1.5 MeV/u. To minimize the possibility of beam loss in the downstream superconducting linac and maintain high acceleration efficiency, we take the 99.9% longitudinal beam emittance as the key optimization parameter for the beam dynamics design of the RFQ, and include an internal buncher to reduce the longitudinal beam emittance. This paper describes the design procedures, beam dynamics simulations and preliminary beam commissioning results for this RFQ. Simulation results show that 99.9% longitudinal beam emittance at the RFQ exit is optimized to 3.5 pi mm mrad, which is 0.13 times the longitudinal acceptance of the downstream superconducting linac. Beam commissioning results demonstrate that the RFQ can accelerate 7.8 mA H2+ to 3.11 MeV. The transmission efficiency from a Faraday cup before the RFQ to the beam dump after the RFQ is 97.6%. The measured transmission efficiency agrees well with simulation results at different values for the inter-vane voltage.