# Gigahertz repetition rate thermionic electron gun concept

## TL;DR

This paper proposes a new method for generating high-brightness, gigahertz-repetition-rate electron bunches using a thermionic gun, RF deflection, and ballistic compression, achieving sub-300 femtosecond bunches.

## Contribution

It introduces a novel design combining a thermionic gun, RF cavity, and harmonic modes for high repetition rate electron bunch generation with improved bunch length and brightness.

## Key findings

- Achieves 279 fs electron bunches at 1 GHz repetition rate.
- Demonstrates a method to increase duty cycle to 30%.
- Produces electron bunches with low emittance of 0.089 mm mrad.

## Abstract

We present a novel concept for the generation of gigahertz repetition rate high brightness electron bunches. A custom design 100 kV thermionic gun provides a continuous electron beam, with the current determined by the filament size and temperature. A 1 GHz rectangular RF cavity deflects the beam across a knife-edge, creating a pulsed beam. Adding a higher harmonic mode to this cavity results in a flattened magnetic field profile which increases the duty cycle to 30%. Finally, a compression cavity induces a negative longitudinal velocity-time chirp in a bunch, initiating ballistic compression. Adding a higher harmonic mode to this cavity increases the linearity of this chirp and thus decreases the final bunch length. Charged particle simulations show that with a 0.15 mm radius LaB6 filament held at 1760 K, this method can create 279 fs, 3.0 pC electron bunches with a radial rms core emittance of 0.089 mm mrad at a repetition rate of 1 GHz.