Development of a Field-Emission Type S-band RF-Gun System for High Brightness Electron Source Applications

Electron beams emitted from a cold cathode are thermally stable and mono-energetic with a small phase-space volume*. We have been developing a field-emission type RF-gun system for high brightness electron source applications, including electron scattering/diffraction and tunable coherent X-ray/THz generation. The system consists of a single-gap gun-cavity and an S-band klystron/modulator capable of powering the gun with up to 5.5 MW peak (PRR = 1 Hz, duration = 2.5 μs). The designed gun built with the symmetrised side-couplers has surface field on the cathode ranging 50 – 100 MV/m with 1.3 – 1.7 MW klystron-power and 1.2 field ratio (HFSS). ASTRA simulations also indicate that the gun produces the beam with transverse emittances of less than 1 mm-mrad with 10 – 20 pC bunch charge at 500 keV beam energy. Under the gun operating condition, particle tracking/PIC simulations (CST) show that a single-tip CNT field-emitter** produces short pulsed bunches (~ 1/10 RF-cycle) with small emittance ( 0.01 mm-mrad) and high peak current density ( 10,000 kA/cm²). After the gun is fully installed and commissioned, a CNT-tip cathode will be tested with RF-field emission.