PCHB – Photocathode Research For High Brightness Electron Beams

A german-russian collaboration on research and development of next generation photocathodes

Modern accelerator‐driven light sources such as LCLS, FLASH rely on the performance of the photocathode. The combination of high average current and ultralow emittance required by ERL or X‐ray FEL oscillator driven light source has never been achieved in a photocathode CW electron source. A research platform with the necessary theoretical and practical possibilities to promote cathode development is established between the participating partners:

• Helmholtz-Zentrum Berlin (HZB)
• Helmholtz-Zentrum Dresden-Rossendorf (HZDR)
• Johannes Guttenberg-Universität Mainz (JGU)
• Moscow State University (MSU)
• Saint-Petersburg State Polytechnic University (SPSPU)

The project includes efforts regarding:

Cathode preparation

Helmholtz‐Zentrum Dresden Rossendorf is currently working on Cs₂Te cathodes and will examine the activation and performance of GaAs photocathodes, Johannes Gutenberg University Mainz is currently examining the preparation of CsK₂Sb and has extended experience in the field of GaAs photocathodes, Helmholtz‐Zentrum Berlin is setting up a new cathode preparation system for CsK₂Sb. (Fig. 1)

Cathode handling

A transport system is developed that allows carrying sample cathodes between the institutes in vacuum. This improves testing and characterization options in various injector systems and with specialized surface science techniques. The system will be compatible to load-locks of the injector systems and preparation and characterization chambers in all participating institutes. (Fig. 2)

Cathode characterization & operational testing

Response time measurements will be carried out at JGU, including an upgrade of the existing system to 0.5 ps resolution, where data taking and analysis is done cooperatively with SPSPU. Surface characterization is possible at a dedicated chamber of HZB’s preparation system and in setups at the synchrotron light source BESSY II where X-Ray diffraction and photoemission spectroscopy measurements can be performed.
Existing injector systems at HZDR (the ELBE SRF injector) and the prototype SRF injectors for bERLinPro serve as test environments for prepared cathodes.

A compact momentum meter will be developed at HZB to allow resolution of the longitudinal and transversal energy distribution of electron beams. The group at MSU will take part in the development by fundamental physics studies for the thermal emittance measurement and energy spectrometer systems.