A new system to trigger fast rise thyristors

Four bump magnets were installed in the KEK (Japan National Laboratory for High Energy Physics) booster ring in order to shift the closed orbit toward the stripping foil during the H^- ion beam-injection period. The bump magnet power supplies are of the pulse forming network (PFN) type. Energy stored in the PFN is delivered to the magnet load via a series array of 32 thyristors. These thyristors must be turned on simultaneously. If there are any differences in the turn-on time, excessive high voltage is added to the thyristor which has the latest turn-on time. To solve this problem, a new trigger system was developed. Turn-on timing pulses are generated in a low-voltage circuit. Each timing pulse is adjusted independently with an accuracy of 0.1 μs and converted to an optical pulse. These optical pulses are transmitted to the high-voltage circuits through optical fibers. The phototransistors deliver the pulse current from the capacitor to the gate of the thyristors, which are fired with an accuracy of 0.1 μs. The simultaneous turning-on of all thyristors in series is made possible with this method, in spite of the fast rise time of the current and the scattering of the characteristic delayed turn-on times