Cryogenic processes of SuperKEKB superconducting magnet cryostat with continuous flow of saturated liquid helium

Abstract

SuperKEKB is a particle accelerator to collide electron and positron beams and employs 55 superconducting (SC) magnets which are accommodated in two cryostats and cooled by subcooled liquid helium (LHe) of ∼ 20 g/s from refrigerators. One cryostat was set up in laboratory for exciting tests and cooled by continuous flow of saturated LHe (<3.0 g/s) from dewars of 1000 L. The differences of two cooling schemes of subcooled and saturated LHe were investigated and described in this paper. The required liquids to cool down the cryostat cold mass (>1700 kg) to 4.5 K were evaluated with a quantified utilization of vapor sensible heat, which fills the large gap between the maximum and minimum liquid requirement presented in most cryogenic literature. The saturated LHe flow was computed to ensure LHe accumulation in the cryostat and immerse SC magnets. The cryogenic processes were monitored by the measured cryogenic temperatures, pressures, flow rates and resistances of SC magnets, which demonstrate cryogenic stabilities with two-phase helium flow and illustrate the agreements with the thermal studies and analyses. This study provides a successful experience to cool SC magnet cryostats of large cold mass with continuous flow of saturated LHe from dewars instead of cryogenic refrigerators.