Experimental operation of a 17 GHz photocathode RF gun

Initial operation of a 17 GHz RF photocathode electron gun has been achieved at MIT. This is the first photocathode electron gun to operate at a frequency above 2.856 GHz. Such electron guns have the potential for achieving record high values of electron beam quality. The 1.5 cell, pi-mode, copper cavity was tested with 5-10 MW, 100 ns, 17.145 GHz pulses from a klystron amplifier built by Haimson Research Corp. Conditioning resulted in a maximum surface field of 250 MV/m. Dark current of 0.5 mA was observed at 175 MV/m, consistent with Fowler-Nordheim field emission theory if a field enhancement factor of about 100 is assumed. Electron bunches were generated by a regenerative laser amplifier that produces 20-40 mu J UV pulses. Faraday cup measurements indicated 0.12 nC bunches were produced with a kinetic energy of about I MeV. This corresponds to a peak current of about 120 A, and a density at the cathode of 8.8 kA/cm(2). Phase scans of laser induced emission reveal an overall phase stability of better than +/-20 degrees corresponding to +/-3 ps synchronization of the laser pulses to the microwave field.