In-situ measurements of the intrinsic emittance of photocathodes for high brightness electron beams

TL;DR

This paper presents in-situ measurements and analysis of the intrinsic emittance of photocathodes, focusing on alkali antimonides like K2CsSb, to improve high brightness electron beam sources.

Contribution

It introduces a new experimental setup for in-situ characterization of photocathodes and provides insights into their fabrication and emission properties.

Findings

Development of a spectrometer for in-situ emittance measurement

Analysis of alkali antimonide cathodes' properties and fabrication process

Insights into factors affecting photocathode quantum efficiency and emittance

Abstract

The beam parameters of complete prototype of the bERLinPro injector that consisted of a lead cathode in an 1.6 cell superconducting cavity were measured. The measurements are discussed in chapter 2 and indicate that the beam emittance is governed by a multitude of contributions from the cathode and the injector. Cathodes for practical use must have a high enough QE to deliver the required current at moderate illumination intensities and be able to sustain the operation for several days. Alkali antimonides are good candidates for this purpose, as discussed in chapter 3.2. The preparation of such cathodes with QEs of a few percent in the visible range has been performed routinely but the details of the growth and the influence of process parameters on the cathodes properties are not well understood yet. A theoretical treatment of photoemission is presented, and expressions for quantum effciency and initial emittance of photocathodes are reviewed in section 3.1. In order to study Potassium Caesium Antimonide (K2CsSb) cathodes and their fabrication a preparation and characterization system has been developed at HZB. In section 3.2 this experimental setup is explained, details of the alkali antimonide cathodes are discussed, and the preparation of a caesium antimonide cathode is presented. Finally, chapter 4 focuses on the physics and engineering design of spectrometer that will resolve the initial transverse momentum of the photoelectrons released from cathode samples, the momentatron. It is installed in the analysis chamber of the cathode preparation system and allows in-situ characterization of the samples.