Patent ID: 8736199

Claim:
An electron gun comprising: an RF cavity defining an internal volume for supporting an electromagnetic field having an RF electric field component within said volume when microwave power is supplied to said cavity; a source that supplies microwave power to said cavity during a sequence of intervals referred to as microwave pulse intervals; a cathode for emitting electrons, said cathode being mounted in said cavity such that electrons emitted from a front surface of said cathode enter said volume and are subjected to said RF electric field component wherein at least some electrons are backstreaming electrons that heat said cathode; and a pulsed illumination laser that illuminates said front surface of said cathode during one or more intervals preceding respective microwave pulse intervals wherein light from said illumination laser produces a thermal pulse at said front surface of the cathode prior to the respective microwave pulse interval, and heat produced by said thermal pulse is conducted away from said front surface of the cathode during the respective microwave pulse interval thereby lowering the temperature at said front surface of said cathode, thereby at least compensating said heat generated by the backstreaming electrons.