Wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron

Irie, Yoshiro; Dooling, J.*; Horan, D.*; Kustom, R.*; Middendorf, M.*; Pile, G.*; Bayley, D.*; Cross, G.*; Gardner, I.*; Glover, M.*; Jenkins, D.*; Morris, A.*; Seville, A.*; Stoneham, S.*; Thomason, J.*; Western, T.*; Fukumoto, Sadayoshi*; Muto, Kenichi*; Oki, Toshiyuki*; Takagi, Akira*; Takano, Susumu*

Wideband low-output-impedance RF system for the second harmonic cavity in the ISIS synchrotron has been developed by the collaboration between ANL (US), KEK (Japan) and RAL (UK). Low output impedance is realized by the feedback from plate to grid of the final triode amplifier, resulting in less than 30 ohms over a wide frequency range of 2.7 - 6.2 MHz. The vacuum tubes in the driver and final stages are both operated in class A. High power test was performed with a ferrite-loaded second harmonic cavity, where the bias current was swept at 50 Hz repetition rate. The maximum voltage of 12 kV peak per accelerating gap was obtained stably at earlier period of an acceleration cycle. A beam test with this system is planned at the ISIS synchrotron soon.