A long-standing collaboration with CERN's CLIC injector group to characterise the performance of their Caesium Telluride photocathodes has progressed. A critical first step has been the design and installation of vacuum equipment which interfaces with the CLIC photocathode preparation facility at CERN and permits the transfer of photocathodes created by them into a vacuum suitcase for transportation to Daresbury Laboratory (DL). Work to install and test this equipment at CERN was completed successfully just a few weeks ago.
Photocathode samples (similar to ice hockey pucks) are now being manufactured from high-purity copper and polished to very low levels of surface roughness. These act as the photocathode substrate onto which the CERN team will deposit the Caesium Telluride photoemitting layer. The cathode 'pucks' should arrive with the CERN team around the end of July.
CERN plan to make four Caesium Telluride photocathodes and load them into the vacuum suitcase which will then be disconnected from the preparation system and transported overland while maintaining ultra-high vacuum. The photocathodes should arrive at DL about 24 hours later, hopefully still under vacuum, and will then be loaded into our experimental systems so that we can carry out a number of characterisation and performance measurements which CERN are not able to make themselves in-house.
We plan to measure the transverse energy spread of the photoemitted electron beam (the cathode's 'intrinsic emittance') using our TESS[1] instrument under illumination at a range of different wavelengths. We will also characterise the surface elemental composition using XPS[2], the surface roughness using AFM[3], and the QE[4]. The intrinsic emittance and the QE are critically important performance characteristics for a photocathode electron source, along with its operational lifetime.
The photograph shows the DL team working with the CERN team after successful testing of our equipment in the CLIC photocathode preparation laboratory. From left to right: Harsha Panuganti, Ryan Cash, Lee Jones, Tim Noakes (DL Team Leader), Eric Chevallay and Valentin Fedosseev (CERN Team Leader). You can see the horizontal sample transfer manipulator in front of Eric and Lee, and the vertical vacuum suitcase manipulator behind Valentin's right shoulder.
[1] Transverse Energy Spread Spectrometer – http://accelconf.web.cern.ch/AccelConf/FEL2013/papers/tupso33.pdf
[2] X-Ray Photoelectron Spectroscopy – https://en.wikipedia.org/wiki/X-ray_photoelectron_spectroscopy
[3] Atomic Force Microscopy – https://en.wikipedia.org/wiki/Atomic_Force_Microscopy
[4] Quantum Efficiency – https://en.wikipedia.org/wiki/Quantum_efficiency
