Study on Thermionic RF Electron Gun after Retuning Process

Abstract

Relativistic femtosecond electron bunches can be produced from the electron accelerator system at the PBP-CMU Electron Linac Laboratory of the Plasma and Beam Physics (PBP) Research Facility, Chiang Mai University (CMU). A thermionic radio-frequency (RF) gun is used as an electron source for this accelerator. The RF gun has a 1.6-cell standing-wave structure with side-coupling cavity. The 2856 MHz RF wave is transmitted from the klystron to the gun through a waveguide system. So far, two RF guns have been used at our laboratory. The first gun was designed and constructed mostly in Thailand. The second one was constructed at the National Synchrotron Radiation Research Center (NSRRC), Taiwan, R.O.C. It was then transported from the NSRRC to our laboratory and was tested after the cavity retuning process. The low-level and high-level RF measurements were conducted. This gun has a resonant frequency of 2855.68 MHz at 26.2°C with a quality factor of 12264. The high-power RF measurements showed that an optimal operating temperature of the gun was 34°C. The electromagnetic (EM) field distribution inside the gun was simulated by using the 3D-model created with program CST Microwave Studio 2012@. Study of electron beam dynamics in the gun using program PARMELA was done to estimate the beam properties at the gun exit. Moreover, measurements of the beam properties were performed. The results showed that at optimal conditions the RF gun could produce the beam of ∼2 μs (FWHM) pulse width with a charge of 850.1 ± 34.7 nC. The major fraction of the beam has an energy in the range of 1.5-2.5 MeV.