Burst-mode electron gun pulser for FEL with the ISIR linac

Infrared free-electron lasers (FEL's) are being developed at The Institute of Scientific and Industrial Research (ISIR). For a FEL oscillator, a burst-mode electron gun pulser with short pulse widths and high repetition rates is effective to obtain multi bunch beams of high peak currents. In order to produce narrow pulses at a 36.9 ns interval, RF of two different frequencies, 27 MHz (fundamental) and 81 MHz (the third harmonic), has been combined with a 3 dB hybrid coupler. The pulses have been directly supplied to the cathode of a high-current electron gun (Model-12, ARCO). The electron beam from the gun at an energy of 100 keV has a peak current of 440 mA in a micropulse with a width of 4.5 ns (FWHM), whose frequency is 27 MHz for a macropulse duration of 4 micro second. After acceleration at an energy of 23 MeV, the charge of an election bunch and energy spread have been measured to be 1 nC and 0.9%, respectively, which shows good performance of the present pulser for FEL oscillator experiments. The grid pulser will be improved to make the repetition rate of the micropulse changeable. >