Cs 2 Te Photocathode for SRF Gun in

Cs 2 Te Photocathode for SRF Gun in Rossendorf Jochen Teichert, Rong Xiang Research Center of Rossendorf, Germany Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE

Outline 1. 2. 3. 4. Introduction Preparation chamber and transfer system Preparation process: co-evaporation The result of first test Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

1. Introduction Cathode transfer rod HOM filter LN 2 reservoir cathode cooler cathode choke filter gun half-cell He-vessel power coupler Normal-conducting cathode inside SC cavity Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

What we need ? Cath Laser necessary Gun Micro. Pulse Laser project Q. E. Qbunch Imean Pmean Epulse Pmean ELBE 13 MHz normal >1% 77 p. C 1 m. A 0. 47 W 36 n. J 0. 8 W 60 n. J high charge 1 MHz >1% 1 n. C 1 m. A 0. 47 W 470 n. J 1. 0 W 1 µJ Bessy mode 1 k. Hz >2. 5% 2. 5 n. C 2. 5 µA 0. 47 m. W 470 n. J 1. 0 W 1 µJ Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE Epulse 06. 11. 2020

Cs 2 Te cathode parameter previously necessary international Q. E. 0. 2 -0. 5 % >1 % >4. 5 % Life time ? 1. 2 k. C 330 h @ 1 m. A (8 weeks) 1. 2 k. C 450 h @ 750 µA Dark current Small Very small average current density 32 m. A/cm 2 @ r = 1 mm 21 m. A/cm 2 damage by Laser 263 nm 32 W/cm 2 @ r = 1 mm 6 W/cm 2 heat load 1 W electric field strength 22 MV/m Mitglied der Leibniz-Gemeinschaft 50 MV/m 125 MV/m Radiation Source ELBE 06. 11. 2020

Old Cs 2 Te cathode in Rossendorf Eccentric position Inhomogeneous Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

1. New Preparation Chamber • New clean room (Class 1000), independent from gun • Ultra high vacuum (P < 10 -9 mbar ) • Measurement of Q. E. – 262 nm laser – Q. E. during deposition – life time – distribution scan • Mitglied der Leibniz-Gemeinschaft Controlled by computer Radiation Source ELBE 06. 11. 2020

evaporators shutter rate monitors laser light ports cathode • Cathode plugs – made of Cu or Mo – optical polishing • Cathode holder – two rate monitors – Halogen light heating – 6 k. V voltage • Evaporators – four boats, easy to change – monitored in a precision of 5 m • Cathode shutter – three positions controlled by PC Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Cathode plug bayonet fixing pressure spring • Made of Cu or Mo • Surface preparation: – optical polishing – cleaning – heating cone for positioning & thermal contact – ion beam bombarding Ø 10 mm Cs 2 Te • Manual Polishing result: Ra= 17. 2 nm (analyzed by Dektak 8 profiler) Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Cathode shutter • three positions controlled by PC 2. To test the deposition rate 1. Sources outgas 3. Start evaporation Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Evaporators and thickness monitors • Evaporators – 87 mm from the cathode – four boats, easy to change – Cesium source SAES Getters • manually manipulated – monitored in a precision of 5 m • two rate / thickness monitor – precise of 0. 01 Å/s, 0. 01Å – 36 mm away from the cathode – calibrated before experiment Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Control system Control program “SRFgun” Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Transfer system cathode transfer root linear & rotation places for 6 cathodes transportation chamber exchange chamber Minimum particle generation during exchange Six cathodes can be stored and transferred Accurate adjustment Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

3. Preparation process Preparation technology standard method co-evaporation sandwich method NCs 2 = R= NTe 1 Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Co-evaporation • • • Advantage: more uniform Open questions: the deposition rate / thickness of Cs film? technology of stoichoimetric rate control? Our solution: Calculate mass factors Te thickness Prepare sample Te+Cs. Te Cs/Te rate - R Film thickness on sensors Prepare cathode Rate on sensors Cs. RTe s 1, s 2 Mitglied der Leibniz-Gemeinschaft Control in situ Radiation Source ELBE 06. 11. 2020

For example Process: 1. the whole wafer is covered by uniform Te film 2. only half of the sample is deposited with Cs film 3. Measure the Cs/Te rate: RBS and PIXE care about only the number of certain nucleus, but not their chemical status. 4. Calculate Cs deposition rate and the mass factors. 5. Calibrate the stoichiometric rate. sample #05 -05 -31 Cs. Te on Cu activated by Cs Te film activated by Cs RBS: Cs/Te=0. 44 PIXE: Cs/Te=0. 55 (calculated by XRUMP, from S. Zhou) (calculated by GUPIX, Dr. Grambole) Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

4. The first test • The preparation methods (standard, sandwich and coevaporation) have been tested. • The photocurrent of several microampere has been detected, corresponding to Q. E. of 0. 5%, which is affected by the unclean chamber and thus the bad vacuum. cathode produced in first test Mitglied der Leibniz-Gemeinschaft Photocurrent pulses Radiation Source ELBE 06. 11. 2020

Current status • • • The chamber has been cleaned and the vacuum reaches 10 -9 mbar. The transfer chambers have been installed; The preparation experiments will start from October 2006. Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Welcome to the website: http: //www. fz-rossendorf. de/projects/CARE/. Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Thank you! Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020

Cs/Te Sample Su No. b. Thick. 1 2 PIX E RB S #05 -0531 Cu 10 nm 20 nm 0. 5 5 0. 4 4 #05 -0616 Cu 10 nm 68 nm 1. 9 #05 -0622 Si 10 nm 70 nm 1. 6 #05 -0623 Si 10 nm 46 nm 0. 8 Mitglied der Leibniz-Gemeinschaft Radiation Source ELBE 06. 11. 2020