An ultra-thin-walled solenoid for the CELSIUS/WASA experiments

Abstract

Abstract An ultra-thin-walled superconducting warm bore solenoid has been developed for the WASA detector set-up at the CELSIUS accelerator of the The Svedberg Laboratory (TSL), Sweden. It gives a central magnetic field up to 1.3 T , and can be operated in persistent mode. The total thickness of the superconducting coil is 9 mm with an inner diameter of 554 mm and an energy-to-cold-mass ratio of 6 kJ / kg . The total wall thickness is a record low 0.18 in units of the radiation length ( X 0 ) including the material of the cryostat. The solenoid has been successfully operated in combination with the WASA detector set-up since 1998. The solenoid has a coil split in two parts with a central gap of 40 mm for a tube guiding small frozen hydrogen target pellets into the accelerator beam. The solenoid is fixed by glass-fibre supports. It has a vacuum vessel with 1 mm thick corrugated walls of aluminium and it has high-purity aluminium strips in axial direction to improve heat conduction. The solenoid is enclosed by an iron yoke which shields the detector readout electronics from the magnetic field. A diagnostics, control and safety system has been developed for the solenoid itself and for the associated cryogenics.