A unique power supply for the PEP-II klystron at SLAC

Each of the eight 1.2 MW RF klystrons for the PEP-II storage rings require a 2.5 MVA DC power supply of 83 Kv at 23 amps. The design for the supply was base on three factors low cost, small size to fit existing substation pads, and good protection against damage to the klystron including klystron gun arcs. The supply uses a 12 pulse 12.5 KV primary thyristor "star point controller" with primary filter inductor to provide rapid voltage control, good voltage regulation, and fast turn off during klystron tube faults. The supply also uses a unique secondary rectifier, filter capacitor configuration to minimize the energy available under a klystron fault. The voltage control is from 0-90 KV with a regulation of <0.1% and voltage ripple of <1% P-P, (<0.2% RMS.) above 60 KV. The supply utilizes a thyristor crowbar, which under a klystron tube arc limits the energy in the klystron arc to <5 joules. If the thyristor crowbar is disabled the energy supplied is <40 joules into the are. The size of the supply was reduced small enough to fit the existing PEP transformer yard pads. The cost of the power supply was <$140 per KVA.