  The design, construction, and commissioning of a conduction-cooled Nb3Sn
demonstration superconducting radio frequency (SRF) electron accelerator at the
Institute of Modern Physics of the Chinese Academy of Sciences (IMP, CAS) will
be presented. In the context of engineering application planning for Nb3Sn
thin-film SRF cavities within the CiADS project, a 650MHz 5-cell elliptical
cavity was coated using the vapor diffusion method for electron beam
acceleration. Through high-precision collaborative control of 10 GM cryocooler,
slow cooldown of the cavity crossing 18K is achieved accompanied by obviously
characteristic magnetic flux expulsion. The horizontal test results of the
liquid helium-free (LHe-free) cryomodule show that the cavity can operate
steadily at Epk=6.02MV/m in continuous wave (CW) mode, and at Epk=14.90MV/m in
40% duty cycle pulse mode. The beam acceleration experiment indicates that the
maximum average current of the electron beam in the macropulse after
acceleration exceeds 200mA, with a maximum energy gain of 4.6MeV. The results
provide a principle validation for the engineering application of Nb3Sn
thin-film SRF cavities, highlighting the promising industrial application
prospects of a small-scale compact Nb3Sn SRF accelerator driven by commercial
cryocoolers.
