One microsecond Pulse-width Annular Beam Relativistic Klystron Operating at 500 MW

This paper describes the experimental development of a long pulse high current, annular beam relativistic klystron amplifier. The desired performance parameters are 1 GW output power and 1 {mu}s pulse length with an operating frequency of 1.3 GHz. the electron beam voltage and current are nominally 600 kV and 5 kA. Peak powers approaching 500 MW have been achieved in pulses of 1 {mu}s nominal baseline-to-baseline duration. The half power pulse width is 0.5 {mu}s. These pulses contain an energy of about 160 J. The rf output terminates abruptly just before the highest parts of the beam voltage and current pulses are reached. The cause of the premature termination of the rf pulse has not been definitely determined. Experimental observations indicate that the rf pulse termination could be the result of the output cavity gap voltage being too high, causing electron reflection at the gap and rf breakdown across the gap. To reduce the output gap voltage, a new output cavity has been designed with a much lower shunt impedance and a loaded Q of 4. Current experimental results and theoretical design considerations for this class of tube are discussed.