Stable Acceleration of a LHe-Free Nb3Sn demo SRF e-linac

Abstract

Abstract The design, construction, and commissioning of a novel liquid helium-free (LHe-free) Nb3Sn superconducting radio frequency (SRF) electron accelerator at the Institute of Modern Physics of the Chinese Academy of Sciences (IMP, CAS) will be presented. A 650 MHz 5-cell elliptical cavity was coated using the tin vapor diffusion method for electron beam acceleration. The cavity was slowly cooled down across 18 K with the high-precision collaborative control of ten individual GM cryocoolers. This process was accompanied by the characteristic magnetic flux expulsion of Nb3Sn films. Horizontal tests of the LHe-free cryomodule show stable operation in both continuous wave (CW) and pulse modes, with maximum peak electric fields (Epk) of 6.02 MV/m and 14.90 MV/m, respectively. The Nb3Sn SRF electron accelerator achieved stable beam acceleration, reaching a maximum energy of 4.6 MeV with an average macropulse beam current exceeding 100 mA. Additionally, stable electron beam acceleration was achieved for the first time at a cavity temperature of 10 K. This pioneering achievement demonstrates a principal validation for the feasibility of applying Nb3Sn thin film SRF cavities in both large-scale scientific facilities and compact industrial accelerators. It also opens up possibilities for further upgrades in operating temperature, cooling methods, and refrigeration equipment for SRF accelerators.