A LONG-PULSE THYRISTOR-SWITCHED MODULATOR FOR THE JHP PROTON LINAC

A long-pulse, high-duty klystron modulator which was fabricated as a prototype for the JHP I-Ge V proton linac has been operated at 15 MW peak power, 400 JJ.s pulse width and 50 Hz repetition rate l • 3 }. This modulator is of a line type which has a pulse forming network switched by two thyratrons in parallel. From a viewpoint of reliable operation and long lifetime it seems that thyratrons are unsuitable for our use of long-pulse and high-average currents (now, 15 A at 400 JJ.S pulse width and, final, 23 A at 600 JJ.s); therefore we must develop the use of SCR or GTO thyristors in place of the thyratrons. Prior to the construction of the full rate thyristor switch, the SCR-stack and GTO-stack modules with a 10 kV hold-off voltage were built and tested in the modulator with a klystron load through a pulse transformer. The design considerations and the test results are reported.