Abstract
We developed a compact SR magnet which is operated at 3. 5T(350A) at persistent current mode. This SR magnet is used for the light source of X ray lithography. If the SR magnet is located at the semiconductor factory, the magnet needs to be highly reliable for a long term persistential operation. The coil should be protected from a large terminal voltage due to its high inductance in case of quenching even if it is a rare accident. We evaluate the coil voltage and developed an active coil protection system for long term persistent operation. This system is composed of the quench detector, external resistive heaters and current power supplies for those heaters. Each components are connected to UPS (uninterruptive power supply) that can supply power for 15 hours with batteries. We can lower the maximum quench voltage to the sufficient safety level that is about 1, 000V by using this active coil protection system. We have obtained total 40, 000hours of operational experiences of this superconducting magnet at persistent current mode without any trouble. At present, this magnet is under successive operation for nearly one year. Through these operations, we have confirmed the high reliability of this superconducting magnet.
