Test Results of Superconducting Combined Function Prototype Magnets for the J-PARC Neutrino Beam Line

Superconducting combined function magnets are adopted for the 50 GeV, 750 kW proton beam line for the J-PARC neutrino experiment, and two full-scale prototype magnets have been developed successfully at KEK. In the cold tests, both prototypes were excited up to 7700 A without spontaneous quenches. The measured field quality of the both prototypes agreed well with the design field, indicating that the fabrication process has no major problem. The heater quench tests of the first prototype, however, showed that the magnet was not self-protected. Consequently, the design was revised and quench protection heaters were adopted. In quench heater tests of the second prototype magnet using small sheet heaters, the fundamental characteristics of the quench protection heaters were studied.