Long-Pulse Modulator for the Superconducting RF Test Facility at KEK

Summary form only given. This paper presents two type of long-pulse 1.3 GHz klystron modulator recently developed for the Superconducting RF Test Facility(STF) at High Energy Accelerator Research Organization(KEK). The STF is a project at KEK to build and operate a test linac with high-gradient superconducting cavities, as a prototype of the main linac systems for International Linear Collider(ILC). This plan includes phase I and phase II. In the phase I, two modulators are used to drive a klystron respectively. One is a direct-switched type design with a 1:6 step-up transformer and a bouncer circuit to compensate the output pulse droop within +/-0.5% during the rf drive period, and operates a single-beam klystron up to 5 MW peak power, 1.5 ms rf pulse width and up to 5 pps repetition rate. This modulator was converted from a short-pulse klystron modulator system inherited from Power Reactor and Nuclear Fuel Corp. The other is also a direct-switched type design with a 1:15 step-up transformer and a bouncer circuit, and operates a multi-beam klystron up to 10 MW peak power, 1.5 ms rf pulse width and up to 5 pps repetition rate. The main features of this modulator are the uses of four 50 kW switching power supplies in parallel to charge the storage capacitors to 10 kV, self-healing type of capacitor to realize a compact storage capacitor bank, and a high reliable series IGBT switch. The design, specifications and performance tests are described.