CERN Lab activities related to PHIN 1. DC and RF gun results with cesium telluride photocathode : a) Cathode produced by the standard evaporation process b) Cathode produced by co-evaporation 2. CTF3 photocathode requirements 3. Photocathode studies: CERN proposal 4. The CTF3 photo-injector: CERN part 5. Installation 6. Schedule G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Standard evaporation process : Cs 2 Te typical results Standard evaporation process means : evaporation of an alkaline layer over a tellurium layer on different substratum Typical results with Cs 2 Te DC gun (35 cath.) RF gun (49 cath.) Nom. electric field 8 MV/m 100 MV/m Peak current 20 A Few kA Pulse width (FWHM) 6 ns 10 ps 8 µ A Higher mean current 1 mA Best substratum Au Cu – Au (?) 4 % ≤ QE ≤ 22 % 2 % ≤ QE ≤ 8 % Starting QE Typical lifetime with QE > 1.5 % Few months (extrapolated) Few weeks 10 -10 mbar 1 – 5 x10 -9 mbar Working vacuum pressure few 10 -11 mbar 10 -10 mbar Storage vacuum pressure G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Standard evaporation process : High charge test (mC) Cs 2 Te photo-cathodes tested in the DC gun @ 9 MV/m Up to 300mW UV on the cathode ; 100 ns pulse length, 10 A, 1kHz Rep.Rate 5.4 µ C macro-pulse CTF3 requested 10 Hz charge 40 working hours CTF3 average current CTF3 QE min J max = 21 mA/cm 2 CTF3 F max = 6 W/cm 2 @ 266 nm requested lifetime CTF3 QE min Up to QE min = 3 % Cs 2 Te photo- cathodes fulfill CTF3 specifications G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Recap of photocathode studies Since 1991 we tested many sorts of photocathodes : Metallic photocathodes : Al, Au, Cu, Mg, Mo, Sm, Y 1. QE < 10 -3 even with special treatment (etching, laser conditioning) � QE too low for high charge production : very high powerful laser and/or plasma production at the � photocathode. Not suitable for our application Alkali-antimonide photocathodes : Cs 3 Sb, K 2 CsSb, K 3 Sb 2. Need ultra high vacuum � � Good QE at visible light but lifetime too short (few hours) not suitable for our application Alkali-telluride photocathodes : Cs 2 Te, Rb 2 Te, RbCsTe, Li 2 Te 3. � Need UHV � RbCsTe and Rb 2 Te : possible rejuvenation after air exposure by heating or etching � Cs 2 Te : standard photocathode for our applications : few % during weeks at high charge and high electric field (up to 120 MV/m) Other photocathodes : CsI, CsI+Ge, Cs 3 As, GaAsO, PLZT, TiO 2 4. CsI+Ge had been used from 1994 to 2000 in the Probe Beam RF gun because it is air transportable � � We had no success with the GaAs activation for e-pol. production : preparation chamber not adapted to this application Photocathodes were deposited on different substrates (Al, Au, Cu, Mg, Mo, Stainless Steel) chemically cleaned and/or cleaned by argon ion bombardment : Cu with chemical and etching cleaning with RF conditioning seems to be the best for high electric field. G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Co-evaporation process QE(t) = QE 1 .e (-t/ τ 1) + QE 2 .e (-t/ τ 2) 20 cath. QE(%) 14 Min 8.2 Mean lifetime (4 cath.) in the DC gun @ 8 MV/m 12 p ≤ 10 -10 mbar Average 14.9 10 Max 22.5 QE (%) 8 Mean lifetime (5 cath.) during storage in the T.C. p ≈ 3*10 -11 mbar Cath. 144 6 in the RF gun 4 67 Mean lifetime (9 cath.) in theRF gun 3 % 100 MV/m ; 2*10 -9 ≤ p ≤ 7*10 -9 mbar days 55 h 2 Working hours 0 τ 1 τ 2 QE 1 QE 2 QE = f (t) 0 50 100 150 200 250 300 350 % % (h) (h) Evaporation at room temperature Transport 3.85 18.9 9.17 3311 Tellurium Cesium carrier Thickness 1.3 - 11 3.9 - 49 nm DC gun 2.24 65.9 12.74 779.5 Evap. rate 0.1 – 0.5 0.5 - 2 nm/mn RF gun 9.2 14 3.4 315 G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Photocathode Requirements for the CTF3 - DB � Photocathodes with a QE ≥ 3 % during at least 40 working hours � A photocathode production to guarantee a continuous run of at least 6 months For that we have to do : � A complete maintenance of the preparation chamber and of the transport carrier (for CTF2 and CTF3 thermoionic gun area installation) � Adapt the RF gun transfer chamber (MPC) to the new gun and to the new sites (we assume the same photocathode plug) � Re-use and/or develop an automatic RF conditioning process � Pursue photocathode studies mainly to increase the lifetime, the reproducibility, and to fulfil the CLIC requirements � Design and built new transport carrier and/or MPC for installation in the CTF3 linac area (not scheduled) G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Photocathode studies – CERN proposal Reproducibility of alkali-telluride photocathodes produced by co-evaporation � Study of alkali-antimonide photocathodes produced by co-evaporation � Comparison between telluride and antimonide cathodes for the CTF3 specifications � UV laser beam UV laser beam Te Te thickness Te thickness Shutter Shutter RF RF measurement measurement oven oven Cs Photocathode Photocathode plug plug 36 mm Cs thickness Cs thickness Electron collect. Electron collect. measurement measurement electrode electrode Preparation chamber developments Stoïchiometric ratio measurement � Cs & Te Cs & Te Evaporation rate control � Evaporators Evaporators Evaporator design for co-evaporation � G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
The CTF3 photo-injector 3 GHz RF source Master oscillator λ = 1047 nm 375 MHz f = 375 MHz KLYSTRON RF Network 3 GHz - 30 MW P = 1 W 3 GHz W/ µ Pulse = 2.7 nJ Electron Beam 2.33 nC / µ Pulse Cs 2 Te cath 3 GHz RF gun QE = 3 % Laser Beam Line E = 85 MV/m 0.37 µ J / µ Pulse U = 5.6 MeV 2310 µ Pulses I = 3.5 A Pre-amplifier λ = 1047 nm Total efficiency P QCW = 50 W Pulse shaping IR OUT ⇒ UV cath = 3.6 % W/ µ Pulse =133 nJ Transport carrier Freq. X 4 Time interval Under the responsibility of λ = 262 nm division CLF-RAL ∆ t = 0.667 ns Photocathode Under the responsibility of preparation LAL Orsay chamber Power Amplifier W train = 1.6 J ; P train = 16 kW Under the responsibility of LAL - Orsay λ = 1047 nm CERN 10.3 µ J / µ Pulse Phase coding Collaboration RAL – LOA Pulse width ≤ 10 ps CERN µ s Pulse duration = 100 G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Pulse Train production Time structure generation of the CTF3 Drive Beam Photoinjector RF = 2.99855 GHz Delay of 1 rf period and recombination 333 ps 333 ps 667 ps I 1 ns Second splitting I Even sub-pulse 667 ps Starting sub-pulse 212 bunches : 140.74 ns Odd sub-pulse I 212 bunches : 140.74 ns I = Laser bunch intensity 1.334 ns 106 bunches 2xI 1.334 ns 1.334 ns First splitting 2xI t = 0 4xI Starting PC 53 bunches Two train generation bunches Driver 2.668 ns Pulse shaping : T = starting sub-pulse + 5 odd sub-pulse + 5 even sub-pulse = 1.548 µ s 2120 bunches + starting bunches G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
CTF3 photo-injector: CERN participation � Laser : � Pulse train generation � Pockel’s cell study � Harmonic conversion efficiency study � Laser monitoring � Feedback control, amplitude regulation � Automatic control of the laser beam position � Timing � Photocathodes � Maintenance of preparation chamber, TC and MPC � RF power � Installation and commissioning G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Installation : Photo-Injector in the CTF2 Suppress controlled entry Install controlled entry Install shielding wall Separate the 2 clim. stations CTF 2 Clim. Clim. 5 MeV ; 3.5 A ; 1.5 µ s ; 10 Hz Laser room 30 GHz , 200 MW , 150 MV/m 6 electr. racks 400 ns , 50 Hz , 30 cm TC Dump 1.5 Optical table x MPC 1.5 x 3.5 m 1.5 m RF test stand Photo-injector Wave guide Light Drill holes hole hole 5 m Φ 120 mm CTF 3 G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Installation : Photo-Injector in the CTF3 CTF 2 RF test stand Laser room Light Laser hole hole TC MPC CTF 3 Photo-injector 5 m Photo-injector as the CTF3 source G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
Schedule Realization of the photo-injector option in two steps : Operational photo-injector in the CTF2 in the end of 2006 � � Operational photo-injector in the CTF3 in the middle of 2007 � Installation during the shut-down 2006-2007 � Commissioning spring 2007 G. Suberlucq CERN CARE PHIN JRA2 Meeting 19/11/2003
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