High Performance Operation of a Direct-Current and Superconducting Radio-Frequency Combined Photocathode Gun

TL;DR

This paper presents a hybrid superconducting radio-frequency and direct-current gun capable of producing high-brightness, continuous-wave electron beams with low dark current and stable operation, advancing applications in coherent light sources and ultrafast electron diffraction.

Contribution

It introduces a novel hybrid gun design combining SRF and DC components, enabling stable CW operation with high beam quality and current, suitable for advanced electron beam applications.

Findings

Achieved stable CW operation with dark current below 100 pA.

Produced electron beams with 2.4 MeV energy gain and 0.54 mm-mrad emittance.

Reaching a maximum average beam current of 3 mA at 81.25 MHz.

Abstract

Superconducting radio-frequency (SRF) guns are promising candidates to deliver high brightness continuous-wave (CW) electron beams for new generations of coherent linac light sources, ultrafast electron diffractions, MeV pulsed beam applications, etc. To solve the compatibility problem of semiconductor photocathodes, a hybrid gun combining a direct-current gap and an SRF cavity has been developed. The gun, employing K2CsSb photocathodes driven by a green laser, has been brought into stable CW operation with a dark current below 100 pA, delivering electron beams at an energy gain of 2.4 MeV, an electron bunch charge of 100 pC, and a repetition rate of 1 MHz. A normalized beam emittance of 0.54 mm-mrad has been achieved at the bunch charge of 100 pC and peak current of about 6 A. CW operation at 81.25 MHz repetition rate has also been tested with the maximum average beam current reaching 3 mA.