High power testing of a 17 GHz photocathode RF gun

Summary form only given. We report experimental results on a high gradient 17 GHz RF photocathode gun. The photocathode RF gun is a novel electron beam source intended to meet the requirements set by future high-energy linear colliders and next generation free electron lasers. A coupled pair of pillbox TM/sub 010/-like resonators is excited by sidewall coupled microwaves at 17 GHz. A picosecond ultraviolet laser pulse illuminates one wall of the structure at the axis of symmetry. Electrons are released by the photoelectric effect and are accelerated by the electric field of the microwaves in the cavity. The high frequency of operation raises the RF breakdown limit allowing strong electric fields to be used. In turn, the intense fields result in rapid acceleration of the electrons to relativistic speeds and reduced space charge induced emittance growth. The 1 1/2 cell, /spl pi/-mode, copper cavity was tested with 5-10 MW, 100 ns, 17.145 GHz pulses from a 24 MW Haimson Research Corp. klystron amplifier. A maximum surface electric field of 250 MV/m was achieved corresponding to an on-axis gradient of 150 MV/m. Electric fields were inferred by using directional couplers and the energy balance equation. The gradient was verified by a preliminary electron beam energy measurement using metal sheets as screens and a Faraday cup. Conditioning with -10/sup 5/ shots resulted in a low field emission current, less than 6 mA.