Study on the H⁻ stripping injection for the Rapid Cycling Synchrotron of the China Spallation Neutron Source

Purpose The China Spallation Neutron Source (CSNS) accelerator consists of an 80 MeV H⁻ Linac and a 1.6 GeV rapid cycling synchrotron (RCS). For the injection system, the H⁻ stripping scheme is adopted to inject the Linac beam to the RCS with high precision and high efficiency. The stripping process through foil plays an important role in the injection, and the related beam losses control need to be studied in detail.
Methods In the beam commissioning, the parameters of the stripping foil have been studied, including: structure, material, thickness, stripping efficiency, temperature, and lifetime. The measurement results are compared with the design values and some parameters of the stripping foil are optimized. With a combination of the codes Py-ORBIT and FLUKA, the beam losses caused by the foil scattering and residual H⁻ beam are simulated in detail and then compared with the actual measurement results.
Results A double-layer HBC foil is instead of a single-layer DLC foil. With an actual thickness of 103 µg/cm², the actual stripping efficiency is about 99.8%. The peak temperature of the main stripping foil is about 1400 K in the simulation. The foil lifetime under the design power is about 1.5 months. The beam losses caused by the foil scattering and residual H⁻ beam are the main sources of the residual doses in the injection region.
Conclusion The parameters of the stripping foil have been optimized and some improvements are proposed. The simulation results of the beam losses caused by the foil scattering and residual H⁻ beam are nearly consistent with the measurement results which can provide some references for the CSNS-II.