An induction linac and pulse power system at KEK

A R&D program on a free electron laser(FEL) in the microwave regime is currently in progress at KEK, intending to investigate the feasibility of an FEL as a promising GW order high power microwave source for the two beam accelerator (TBA) scheme in a future high energy linear collider. The first prototype of the KEK FEL was an induction linac driven X-band (9.4 GHz) FEL energized by a 800 keV, 1 kA electron beam. The rf power amplification exceeded 30 MW, however, theoretical work indicated that the 800 keV operation was in the Raman regime and the FEL gain was limited by a strong space charge effect. To cure problems arising from the space charge effect, a new generation of the KEK FEL has been completed, in which the driving electron beam energy was upgraded to 1.6 MeV and about 700 A beam current was successfully transported through a wiggler magnet. In parallel to the FEL investigation, several types of high current induction linacs and a pulse power system were also developed. The pulse power system consists of two gate-turn-off thyristor (GTO) switch modules, two magnetic pulse compressors and a dc high voltage source. A 1.6 kV dc high voltage is resonantly discharged by the GTO switches and its pulse duration is compressed to 200 kV, 100 ns pulse power by a combination of two step-up transformers and three saturable inductors. The induction linacs are of two types. One is loaded by a ferrite magnetic cores (TDK PE14) and the other is loaded by amorphous cores (Metglass 2605S). The details of the induction linacs and pulse power system design and a performance will be reported. >