Concept Study of a Compact, High Gradient X-band Travelling Wave RF Photogun with Novel Laser Coupling Scheme

TL;DR

This paper introduces a novel compact X-band travelling wave RF photogun with a unique laser coupling scheme, achieving high gradients and repetition rates suitable for advanced accelerator applications.

Contribution

It presents a new design of a high-gradient, high-repetition-rate RF photogun with an innovative laser coupling method based on a CLIC prototype structure.

Findings

Achieves a peak gradient of 91 MV/m at the cathode.

Operates at a repetition rate of at least 450 Hz.

Provides an electron bunch with 80 pC at 14.15 MeV, low energy spread, and low emittance.

Abstract

This paper presents the design of a travelling wave RF photogun operating at the European X-band frequency of 11.994 GHz. The design is based on a CLIC prototype structure milled from copper halves and uses the unique gap introduced in the geometry to couple in the laser without obstructing the outgoing electron beam. With a modest peak input power of 19 MW and a fill time of 48 ns, the gun has the ability to operate at very high RF pulse repetition rates in comparison to standing wave RF photoguns. For its nominal input power, the cathode has a peak gradient of 91 MV/m and the entire gun has a gradient of 65 MV/m. The gun is illustrated to provide an 80 pC bunch at a 14.15 MeV with a 0.14 $\%$ RMS energy spread and an emittance of 0.6 mm mrad at a repetition rate of at least 450 Hz.