Development of a Superconducting Solenoid Magnet System for the B-Factory Detector (BELLE)

Abstract

A large superconducting solenoid magnet has been designed and fabricated for the BELLE particle detector, which will be installed in the KEKB colliding beam ring. It provides a central magnetic field of 1.5 T at 4000 A in a cylindrical volume of 3.4 m in diameter and 4.1 m in length. The stored energy is calculated to be 42 MJ. The coil is wound with aluminum stabilized superconductor, after which aluminum strips are laminated on the coil for quench protection. The coil cold mass is approximately 7 tons with an estimated thermal load of 22 W at 4.2 K. A refrigerator of 240 W at 4.2 K is attached. The coil is indirectly cooled by forced flow of 2 phase helium through a cooling tube on the coil support cylinder. This method is preferred in order to avoid explosive boiling which may happen if a pool cooling method was used. A line in the solenoid Is designed to allow the stored helium in the top buffer tank to circulate gravitationally in case of a suspension of cryogen, producing slow discharge without induced quench. This report presents the design and fabrication of the BELLE superconducting solenoid magnet.