Nano-machining, surface analysis and emittance measurements of a copper photocathode at SPARC_LAB

TL;DR

This paper presents a comprehensive study on nano-machining and surface analysis of copper photocathodes at SPARC_LAB, demonstrating how surface treatments influence electron beam quality and exploring yttrium thin film coatings.

Contribution

It introduces a diamond milling process for copper photocathodes that reduces surface roughness and contamination, improving photoemission properties and beam brightness.

Findings

Nano-machining reduces surface roughness and contamination.

Surface quality improvements lead to lower emittance.

Preliminary results on yttrium coatings show potential benefits.

Abstract

R\&D activity on Cu photocathodes is under development at the SPARC\_LAB test facility to fully characterize each stage of the photocathode "life" and to have a complete overview of the photoemission properties in high brightness photo-injectors. The nano(n)-machining process presented here consists in diamond milling, and blowing with dry nitrogen. This procedure reduces the roughness of the cathode surface and prevents surface contamination introduced by other techniques, such as polishing with diamond paste or the machining with oil. Both high roughness and surface contamination cause an increase of intrinsic emittance and consequently a reduction of the overall electron beam brightness. To quantify these effects, we have characterized the photocathode surface in terms of roughness measurement, and morphology and chemical composition analysis by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Atomic Force Microscopy (AFM) techniques. The effects of n-machining on the electron beam quality have been also investigated through emittance measurements before and after the surface processing technique. Finally, we present preliminary emittance studies of yttrium thin film on Cu photocathodes.