Pulsed Power Supply for Magnet Quench Training

Superconducting magnets typically go through a series of spontaneous “training” quenches as their current is increased towards its design value. To decrease the number of these quenches, a device has been designed to boost the magnet current at the moment a quench has been detected and before magnet protection has been initiated. The aim of the boost is to drive the magnet coil further along towards its maximum current with each training quench, and hence reduce the number of quenches required. The current boost is accomplished by diverting the current in the magnet circuit from a diode in series with the load to a charged capacitor (400 mF charged up to 1 kV) connected across the diode. The output terminal of the capacitor is connected to the cathode of the diode by closing an IGBT switch. The connection initially adds up to 1 kV to the magnet voltage and drives its current up rapidly. The voltage on the capacitor bank discharges to zero as its stored energy transfers into an increase in magnet current. The transfer time is some tens of milliseconds, after which standard magnet protection is initiated.