Active Protection of an MgB(2) Test Coil.

This paper presents results of a study, experimental and computational, of a detect-and-activate-the-heater protection technique applied to a magnesium diboride (MgB(2)) test coil operated in semi-persistent mode. The test coil with a winding ID of 25 cm and wound with ~500-m long reacted MgB(2) wire was operated at 4.2 K immersed in a bath of liquid helium. In this active technique, upon the initiation of a "hot spot" of a length ~10 cm, induced by a "quench heater," a "protection heater" (PH) of ~600-cm long planted within the test coil is activated. The normal zone created by the PH is large enough to absorb the test coil's entire initial stored energy and still keeps the peak temperature within the winding below ~260 K.