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Status of the Photocathode R&D for ATF RFgun

Status of the Photocathode R&D for ATF RFgun. N.Terunuma (KEK). Why we use Cs 2 Te photocathode?. Pure metal cathode. Q.E. 10 -5 ~ 10 -4 Cs 2 Te Q.E. ~ 10 -1 , a few % Others Need more study. We prepared the Cs 2 Te formation system and the Cathode loadlock system for ATF.

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Status of the Photocathode R&D for ATF RFgun

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  1. Status of the Photocathode R&Dfor ATF RFgun N.Terunuma (KEK)

  2. Why we use Cs2Te photocathode? Pure metal cathode. Q.E. 10-5 ~ 10-4 Cs2Te Q.E. ~ 10-1 , a few % Others Need more study. We prepared the Cs2Te formation system and the Cathode loadlock system for ATF. For ATF, Shorter preparation time for the beam operation. --> Preparation system connected to the RFGUN.

  3. Cathode Load-lock System RFGUN Cavity Cathode loading mover Cathode formation Laser Cleaning & Pickup Xe light Storage RFGUN

  4. Quantum Efficiency Offline measurement Xe lamp with monocrometer~266nm. Measure the current on cathode. Online measurement RFGUN operation, Laser~266nm. Extracted beam intensity detected by faraday cup. Q.E.= Number of electrons / Number of photons

  5. Cathode and Cs-Te sources 15mm Te Cs Cathode Plug (Cu) Evaporation System

  6. Half cell endplate with Cu plug

  7. Formation: Step 1, Cleaning Step 1: Cleaning Argon ion bombardment When New cathode is installed. Clean the used cathode. Sputter depth ~ 50nm . Ion Source Cleaning chamber

  8. Formation: Step 2, Te evaporation Step 2: Evaporation of Te Te is heated by a Tungsten filament. We can control the Te thickness.

  9. Formation: Step 3, Cs evaporation Step 3: Evaporation of Cs Cs is evaporated on the Te film and its thickness is controlled by monitoring the Q.E. with Xe system. Cathode holder with Mask f8mm

  10. R&D • For the ATF operation… • Prepare the new cathode on Monday. • Beam Test: a week or more. • Check Q.E. by calibrated lights (Xe,266nm) every a few days. • For the basic study… • in shutdown weeks. • This year, we had two months beam operation. • Two Cu plugs • Two Mo plugs

  11. QE of Cu#1 Cathode 1.3x10-6 Pa at RFGUN ATF Yellow area: RF on Q.E. 0.4%

  12. Cu cathode after the Beam Test • Two cathode plugs were used for a month operation. • Cu#1 cathode (left) • Used for the cavity aging. • Many RF breakdowns. • Cu#2 cathode (right) • Used stable laser operation.

  13. Mo Cathode Two plugs ware used for a month operation. Their surface were polished as a mirror. Small damage was found after the beam operation.

  14. Q.E. of Cs2Te on Mo plugs • Q.E. before RF power is supplied reaches > 15%. • Q.E. dropped quickly when RF power was supplied. • It shows stable Q.E. after RF power supplied. • Cs2Te on Molybdenum plugs shows higher Q.E. ~3% than that on Copper plugs ~0.4%.

  15. Dark Current Dark vs. Power (MW)

  16. Summary We had two months beam operation. Cs2Te on Cu plugs Q.E. ~0.4%. Damages on the Cu surface. Cs2Te on Mo plugs Q.E. ~3%. Stable. Small damages compared to Cu case were observed. Next Establish the formation method and its reproducibility. Check Q.E. under longer beam operations.

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