Demonstration of Cathode Emittance Dominated High Bunch Charge Beams in a DC gun-based Photoinjector

TL;DR

This paper demonstrates that high bunch charge beams produced in a DC gun-based photoinjector can achieve low emittance dominated by cathode thermal effects, matching simulations and suitable for advanced accelerator applications.

Contribution

It shows that DC gun photoinjectors can produce high-quality, high charge beams with emittance characteristics previously thought exclusive to RF guns.

Findings

Cathode emittance dominates final beam emittance.

Excellent agreement between simulations and measurements.

Laser distribution limits beam quality.

Abstract

We present the results of transverse emittance and longitudinal current profile measurements of high bunch charge (greater than or equal to 100 pC) beams produced in the DC gun-based Cornell Energy Recovery Linac Photoinjector. In particular, we show that the cathode thermal and core beam emittances dominate the final 95% and core emittance measured at 9-9.5 MeV. Additionally, we demonstrate excellent agreement between optimized 3D space charge simulations and measurement, and show that the quality of the transverse laser distribution limits the optimal simulated and measured emittances. These results, previously thought achievable only with RF guns, demonstrate that DC gun based photoinjectors are capable of delivering beams with sufficient single bunch charge and beam quality suitable for many current and next generation accelerator projects such as Energy Recovery Linacs (ERLs) and Free Electron Lasers (FELs).