Experimental and theoretical investigations of a 17 GHz RF gun

We report on experimental and theoretical investigations of a 17 GHz RF pho tocathode electron gun. This is the first photocathode electron gun to oper ate at a frequency above 2.856 GHz. The 1.5 cell, n mode, copper cavity was tested with 50 ns pulses from a 17.150 GHz klystron amplifier built by Hai mson Research Corp. A Bragg filter was used at the RF gun to reduce the ref lection of parasitic modes back into the klystron. Coupling hole theory in conjunction with cold test measurements was used to determine the field pro file in the RF gun. The particle in cell code MAGIC as well as coupled enve lope equations were used to simulate the beam dynamics in the RF gun. With power levels of 4 MW, the on axis electric field at the cathode exceeds 300 MV/m, corresponding to an average accelerating gradient of 200 MV/m over t he first half cell of the gun. Breakdown was observed at power levels above 5 MW. Electron bunches were produced by 20 mu J, 1 ps UV laser pulses impi nging on the RF gun copper photocathode and were measured with a Faraday cu p to have up to 0.1 nC of charge. This corresponds to a peak current of abo ut 100 A, and a density at the cathode of 8.8 kA/cm(2). Multiple output ele ctron bunches were obtained for multiple laser pulses incident on the catho de. Phase scans of laser-induced electron emission reveal an overall phase stability of better than +/- 20 degrees, corresponding to +/- 3 ps synchron ization of the laser pulses to the phase of the microwave field. A Browne-B uechner magnetic spectrometer indicated that the RF gun generated 1 MeV ele ctrons with a single shot rms energy spread of less than 2.5%, in good agre ement with theoretical predictions. (C) 1999 Elsevier Science B.V. All righ ts reserved.