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

2. 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. For ATF, Shorter preparation time for the beam operation. --> Preparation system connected to the RFGUN.

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

4. Quantum Efficiency Q.E.= Number of electrons / Number of photons 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.

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

6. Half cell endplate with Cu plug

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

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

9. Cs is evaporated on the Te film and its thickness is controlled by monitoring the Q.E. with Xe system. Step 3: Evaporation of Cs Formation: Step 3, Cs evaporation Cathode holder with Mask  8mm

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 ATF 1.3x10 -6 Pa at RFGUN Q.E. 0.4% Yellow area: RF on

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 Cs 2 Te 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 vs. Dark Current Power (MW)

16. Summary We had two months beam operation. Cs 2 Te on Cu plugs Q.E. ~0.4%. Damages on the Cu surface. Cs 2 Te 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.