The fruits from several years of design, procurement, assembly, and system commissioning culminated on Wednesday 18th May with the first successful growth of a caesium telluride (Cs-Te) photocathode using ASTeCs new Alkali metal Photocathode Preparation Facility (APPF), pictured below.
The team of Dr Lee Jones, Hugh Churn, Chris Benjamin, and Dr Tim Noakes deposited a combination of caesium and tellurium onto a copper ‘puck’ to create a photoemissive Cs-Te layer which can act as a high efficiency electron source for a particle accelerator such as CLARA or a future UK X-FEL. The composition scan below shows the Auger Electron Spectrum for the finished layer, clearly evidencing the presence of caesium with binding energy around 560 eV, and tellurium at around 490 eV.
We measured the photoemission efficiency or quantum efficiency (QE) of the layer to be around 0.27%, which may not seem very high in itself, but is around 100 times more than the efficiency of the plain copper photocathode currently used in the CLARA accelerator.
While the initial results are modest in terms of the absolute performance achievable from caesium telluride photocathodes, they are substantial given the compressed timescale over which the work was carried out, following delays due to issues with the equipment and covid. Lee Jones said:
"This is a fantastic result for ASTeC’s photocathode R&D team, and particularly for Hugh Churn and Chris Benjamin who have pushed so hard to achieve this milestone in advance of the IPAC conference. I know that following our recent experience working with CERN to characterise their Cs-Te photocathodes, we can build on this first step in synthesizing these photocathodes on our own dedicated system to hone our manufacturing technique and ultimately produce high-quality, high-efficiency Cs-Te photocathodes for particle accelerator applications."
The team will present the results of our work on the CERN Cs-Te photocathodes, and our own achievements in manufacturing Cs-Te photocathodes at Daresbury at the IPAC ’22 conference in Bangkok next month.
Contact: Dr Lee Jones, Accelerator Physics Group, ASTeC, STFC Daresbury Laboratory
