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COPPER PHOTOCATHODES DEVELOPMENTS AT ASTEC

This document provides an overview of the advancements in copper photocathode technology developed at the Accelerator Science and Technology Centre (ASTEC), UK. It discusses the essential properties of photocathodes, such as high quantum efficiency (QE), fast response time, and low emittance. Emphasis is placed on metal photocathodes' durability and performance under extreme conditions. The work includes photocathode preparation procedures, the impact of surface cleaning techniques, and the effects of operating gas species on QE degradation. The findings aim to enhance photocathode reliability for high-brightness beam applications.

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COPPER PHOTOCATHODES DEVELOPMENTS AT ASTEC

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  1. COPPER PHOTOCATHODESDEVELOPMENTS AT ASTEC R. Valizadeh Accelerator Science and Technology Centre Science & Technology Facility Council, UK

  2. Outline Overview of work done at other accelerator centres Photocathode preparation program at Daresbury Lab

  3. Important Properties of Photocathodes High Quantum efficiency Fast response time Uniform emission Low as possible emittance (atomically flat) Have reasonably high operating life time at vacuum level 10-9 to 10-10Torr range. Easy to fabricate, reliable, reproducible QE and emittance after cathode cleaning and re-activation.

  4. Why Metal Photocathodes Metal cathodes have fast response time 10-15 to 10-14 seconds. They are robust and can survive years at high cathode fields to produce high brightness beam However due to the high work function UV photons are needed for reasonable QE.

  5. Metal Photocathodes

  6. QE and thermal emittance

  7. Variation of Emittance and QE with laser wavelength and spot size

  8. Effect of surface roughness on Emittance.

  9. Survivability and lifetime

  10. Dependence of lifetime on residual operating gas species

  11. Effect of laser surface cleaning for restoring QE

  12. H-ion bombardment and Ozone

  13. Annealing and Ar plasma Cleaning

  14. Photocathode preparation and diagnostic system

  15. QE Measurment setup

  16. Vacuum suitcase for transportation of prepared photocathode to RF Gun.

  17. Initial Programme Establish reliable and reproducible sample preparation procedure to minimise the final surface carbon contamination. (done at SLAC) Prepare atomic flat surfaces for single crystal and poly-crystalline copper. Produce engineered rough surface. Determine QE for different method of surface regeneration (Ar, H and Ozone cleaning) Determination of surface roughness after each procedure. Identify the effect each individual residual gas species(H2, CO, CO2, H2O and CH3) on QE degradation. Optimization of wide band gap coating (CsBr) on copper. Study the effectiveness of the Vacuum suitcase.

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