X-band klystron modulator for the Accelerator Test Facility

An X-band klystron modulator has been designed and constructed to drive two kinds of prototype X-band pulsed klystrons: a 30-MW klystron (XB-50 K) requiring a 450-kV beam voltage with a 0.5- mu s flat top, and a 120-MW klystron (XB-72 K) requiring a 550-kV beam voltage with a 0.5- mu s flat top. The modulator generates 2.0- mu s pulses with 37-kV voltage and 7300-A peak current for the operation of the XB-72 K. It is a conventional line-type modulator with a six-section pulse forming network (PFN) which is resonantly charged and discharged by a thyratron switch at up to 200 p.p.s. To reduce the size of the modulator, a special low-inductance capacitor using film-coated thin Al-electrodes of 300-AA thickness has been developed for the PFN. Its output pulse voltage is stepped up to 15 times by a pulse transformer. The design, specifications and results of performance tests of the modulator are described.<>