High Power Operation of a 17 GHz Photocathode RF Gun

We report the first operation of a 17 GHz RF photocathode electron gun. 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 2 cell, π -mode, copper cavity was tested with 5-10 MW, 100 ns, 17.145 GHz pulses from a 24 MW Haimson Research Corp. klystron amplifier. Klystron power is stable to within ±5% up to 15 MW. Conditioning resulted in a maximum surface field of 250 MV/m, corresponding to an on-axis gradient of 150 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 2 ps, 1.9 mJ pulses at 800 nm with ±10 % energy stability. These pulses were frequency tripled to 46 μ J of UV, and then focused on the wall of the cavity. Preliminary beam measurements indicate 0.12 nC bunches were produced with a kinetic energy of about 1 MeV. This corresponds to a peak current of about 100 A, and a density at the cathode of 2 kA/cm. Both single and multiple pulse laser induced beam emission were observed.