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: (1) 30 MW klystron ( XB-50K) requiring a 450 kV beam voltage with a 0.5 μs flat top and (2) 120 MW klystron ( XB-72K) requiring a 550 kV beam voltage with a 0.5 μs flat top. The modulator generates 2.0 μs pulses with 37 kV voltage and 7,300 A peak current for the operation of the XB-72K. It is a conventional line-type modulator with a 6 section pulse forming network (PFN) which is resonantly charged and discharged by a thyratron switch at up to 200 pps. In order to reduce the size of the modulator, a special low inductance capacitors using a film coated thin Al-electrodes of 300 angstrom 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 in this paper