High-power test of thermionic RF-gun at the Pohang Accelerator Laboratory

A one-cell RF-gun with a dispensers cathode was fabricated for high-brightness applications at the Pohang Accelerator Laboratory. The gun was designed to withstand heavy beam loading and breakdown for long-pulse operation. After some RF-conditioning, the gun could be powered up to a nominal RF-power of 3.5 MW during 6 [[micro]second]. The gun produced an electron beam with an average current of 300 mA and energy up to 1 MeV, normally, operated with a 6-[[micro]second] macropulse and 12-Hz repetition rate. The beam loading and the energy spectra were measured to confirm the gun's performance. The beam emittance was measured and compared with simulation results. The breakdown problem due to the field-emitted electrons and the backward electrons in the gun is discussed. Index Terms - Breakdown, field emission, gas desorption, thermionic RF-gun.