The CERN cryogenic test facility for the ATLAS barrel toroid magnets

The superconducting magnet system of the ATLAS detector will consist of a c entral solenoid, two end-cap toroidal magnets (ECT) and the barrel toroid m agnet (ET) made of eight coils symmetrically placed around the central axis of the detector. The magnets will be tested individually in a 5000 m2 expe rimental area prior to their final installation at an underground cavern of the LHC Collider. For the BT magnets, a dedicated cryogenic test facility has been designed which is currently under the construction and commissioni ng phase. A liquid nitrogen pre cooling unit and a 1200 W@4.5K refrigerator will allow flexible operating conditions via a rather complex distribution and transfer line system. Flow of two-phase helium for cooling the coils i s provided by centrifugal pumps immersed in a saturated liquid helium bath. The integration of the pumps in an existing cryostat required the adoption of novel mechanical solutions. Tests conducted permitted the validation of the technical design of the cryostat and its instrumentation. The characte ristics of one pump were measured and pressure rise of 300 mbar at nominal flow of 80 g/s confirmed the specifications.