Laboratoire de Chimie-Physique CNRS – Université Paris-Sud UMR ORSAY Cs 2 Te photocathodes at ELYSE

Choice of accelerator & cathode Pump probe experiments (synchro. laser & electrons) Small accelerator room (existing building) Photoinjector High charge > 1 nC High Q.E. (Laser energy max ~ 20 µJ) Long lifetime Cs 2 Te

Specifications for accelerator  Pulse duration  5 ps  Charge  1 nC  Energy from 4 to 9 MeV  Repetition rate  50 Hz  Energy dispersion  2,5 %  Diameter on target  2 à 20 mm choice of L.A.L. (SERA)

Photo-injector Laser – 263 nm electrons R.F. gun Booster photocathode solenoid F = 3 GHz Design same as CERN/CTF For RF gun & cathode preparation Chamber (minor changes) F = 3 GHz

R.F. Gun & Booster F = 3 GHz 10 cm R.F. gun Booster 3 MeV 9 MeV

Femtosecond Laser ~ 3 m transport

Accelerator layout Production of electrons acceleration transport RF gun, solenoid, booster laser Preparation chamber (in situ fabrication) Experimental areas triplet triplet

Accelerator Room

Diagnostics 1 m Faraday cup charge Screen transverse beam size W.C.M. charge – position Horizontal slit energy dispersion Cerenkov radiator pulse width

History n January 2000 building construction –creation of L.C.P. n April 2001 accelerator & laser moving form LAL to LCP n Januray 2002 photocathode preparation chamber installation (CP) n April 2002 first beam – 9 MeV (copper cathode) n June 2002 conditionning cavities : 5 Hz - 10Hz - 25 Hz CP leak, buiding chiller problem… n April st cathode CsTe : 6 nC n May st ps – 1,5 nC – 9 MeV n October st local users … beam production for users, minor changes for accelerator n October nd CsTe photocathode ! n … beam production for users

Photocathode Cs 2 Te -  = 20 mm Cs = 16 nm Te = 20 nm Canon HF Section acc. photocathode inside RF gun Preparation chamber Substrat Copper (polished)

Cathode manipulator Cathode fabrication area Cathode Inside RF gun

Te Cs micro-balance 10 cm Cathode fabrication - -Copper substrat cleaned and outgased (400°C – 1h) - Temperature ~ 110°C - Monitoring of thickness during evaporation Te = 20 nm (10 min) Cs = 15 nm (45 min) QE = 0,5% In operation

Preparation Chamber PC Te et Cs crucibles heater micro-balance

Cs 2 Te lifetime Laser diameter = 15 mm Air exposition

Cs 2 Te deterioration 17 juin 2005

Vaccum conditions n P(PC) ~ 3 x mbar (leak –porosity) n P(PC) ~ 5 x mbar during preparation n P(gun) ~ 5 x mbar (static) n P(gun) ~ 5 x mbar (with RF)

Possible improvements n Add in situ current measurement during evaporation for optimisation n Try Mo substrate n Better outgasing n Add closing valve for separating crucible translator (not much space ) …

Accelerator performance   Pulse duration ~ 6 ps   Charge : 0.1 to 6 nC   Energy from 4 to 9 MeV   Repetition rate : Hz   Energy dispersion 1 %   Diameter on target : 2 à 20 mm

Photo-current – Dark current / 50  = 5,8 nC Iobsc Iph laser Eaxe F = 10 Hz HF = 3 µs Laser = 2,7 µs Direct leg : VD 9 MeV Ea = 70 MV/m Qph = 5,8 nC Qdark = 3,9 nC Qdark/Qph = 67% VD VD1 VD2

Klystron – HF distribution 15MW 6 MW MW

Implantation 2ème sous-sol Aires expérimentales K M A 2ème sous-sol, bâtiment 349

Recouvrement - cerenkov Simulation E.G.S. eau verre 1 cm vide diode air eau e- Lumière Cerenkov Recouvrement des faisceaux air

Yag-Ce – 40 mm (200 µm) VD2 – 9 MeV Fwhm = 2 mm saphir – 25 mm (500 µm) VD2 - 9 MeV 30° view angle Fwhm = 3 mm 25 mm 40 mm Beam size measurement (in air) Exit window (12 µm Al) camera vacuum screen

Pulse duration FWHM = 5,8 ps 9 MeV, Q = 1.6 nC time Wave length 380 nm 620 nm Cerenkov light