Parametric studies of 2K cryogenic system for superconducting e-linac at VECC, Kolkata

VECC is developing a 2 mA, 30/50 MeV continuous-wave superconducting electron linear accelerator (e-Linac) for the rare isotope beam facility upgrade. Presently a 10 MeV injector comprising a capture cryomodule (CCM) and an injector cryomodule (ICM) is being developed in collaboration with TRIUMF laboratory in Canada. The CCM and ICM will respectively house two single-cell and one 9-cell niobium superconducting radio-frequency (SRF) cavities operated at 1.3 GHz and 2 K. The 2K temperature is produced by expanding liquid helium from atmospheric pressure to about 30 mbar pressures through a Joule-Thomson (JT) valve. The sub atmospheric pressure is maintained by two roots pumps and a dry backing pump. A 4K-2 K test setup is being developed for testing the cryogenic parameters. A general model is formulated to construct parametric analysis comprising of different components making up the system. The numerical formulation is used for quantitative assessment of the flow requirements under different conditions of operation as well as abnormal scenarios like vacuum failure, rise of thermal shield temperature and so on. The results of the investigation provide a fundamental understanding of the system behaviour and flow requirements during operation. The paper also discusses the intricate relationships among different components of the system along with their desired performance characteristics.