Design study of a low-emittance high-repetition rate thermionic rf gun

Abstract

We propose a novel gridless continuous-wave radiofrequency (rf) thermionic gun capable of generating nC ns electron bunches with a rms normalized slice emittance close to the thermal level of 0.3 mm mrad. In order to gate the electron emission, an externally heated thermionic cathode is installed into a stripline-loop conductor. Two high-voltage pulses propagating towards each other in the stripline-loop overlap in the cathode region and create a quasielectrostatic field gating the electron emission. The repetition rate of pulses is variable and can reach up to one MHz with modern solid-state pulsers. The stripline attached to a rf gun cavity wall has with the wall a common aperture that allows the electrons to be injected into the rf cavity for further acceleration. Thanks to this innovative gridless design, simulations suggest that the bunch emittance is approximately at the thermal level after the bunch injection into the cavity provided that the geometry of the cathode and aperture are properly designed. Specifically, a concave cathode is adopted to imprint an Ƨ-shaped distribution onto the beam transverse phase-space to compensate for an S-shaped beam distribution created by the spherical aberration of the aperture-cavity region. In order to compensate for the energy spread caused by rf fields of the rf gun cavity, a 3rd harmonic cavity is used. A detailed study of the electrodynamics of the stripline and rf gun cavity as well as the beam optics and bunch dynamics are presented.

Electron Injector Based on Thermionic RF-Modulated Electron Gun for Particle Accelerator Applications

“…The RF gun in Fig. 1(a) is placed at the entrance of the RF acceleration cells, and the electron beam will be directly accelerated by the electric field in the cells [3,11,13,14]. It has the advantage that the cathode structure is simple.…”

“…Liang Zhang, Senior Member, IEEE, Georgia Adam, Boris Militsyn, Wenlong He and Adrian W. Cross beam and has attracted a great deal of interest as an electron beam source in RF linacs [11][12][13][14] as the electron micro-pulses can be matched with the acceleration RF buckets as well as achieving control of the emitted electron beam. The charge, length and emittance of the generated electron bunch are important parameters for the thermionic RF modulated gun used in linacs.…”

Rf Modulated Thermionic Electron Gun

“…This makes it possible to obtain at the injector output bunch charge of 77 pC with a normalized emittance of 0.53 μm. Paper [5] describes a combined gun with thermionic CeB 6 cathode. The cathode is installed in a complex form stripline (stripline loop).…”