An independently tunable cells thermionic RF gun (ITC-RF GUN) for Sub-picosecond short pulse

Recently a wavelength region shorter than mm but longer than 100 μm, so-called THz radiation, is paid attention and development of THz sources is rapidly developed, because the THz light is passing through semiconductors like Si but the water is not transparent. These specific characters are completely different from usual X-rays, so that many applications are considered worldwide. The THz radiation is normally produced using conventional lasers via a non-linear crystal. In this case, the power is pretty low but a frequency resolution is better. The most promising high quality THz radiation may be coherent synchrotron radiation emitted from the extremely short electron bunch or Far-IR FEL. Although photo injectors using RF guns are rapidly developed as high brilliant electron sources, meanwhile thermionic RF guns are still expected to have potential ability to create high-brightness and short-pulse beams [1]. In particular, whole system of the thermionic RF gun is simple, compact and low-cost than that of a photocathode RF gun. In addition, a velocity-bunching like effect may be occurred in the gun, so that the short pulse beam from the thermionic RF gun is a better candidate to produce the coherent THz synchrotron radiation. For creating such beams, thermionic RF gun has been designed and its characteristics have been studied by a 3D simulation code developed based on an FDTD (Finite Difference Time Domain) method [2]. The gun is consists of two independent power feeding cavities, so that we call it "independently tunable cells (ITC)"-RF gun. The first cell is a cathode cell to extract the beam and the second one is an accelerating cell. The ITC gun can be operated at modes with different RF-power ratio and phase between two cavities. A similar way of operating RF gun has been already reported by Lewellen [3]. This paper describes the results of simulations for this thermionic RF gun.