CTF3 lasers Marta Csatari Divall Eric Chevallay, Valentine Fedosseev, Nathalie Lebas, Roberto Losito, Massimo Petrarca, CERN, EN-STI CTF3 Collaboration meeting 6 th May 2010

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Results on PHIN Feedback stabilization Phase coding Laser for CLIC Future plans

Photo-injectors for CTF3 Drive Beam Accelerator Delay Loop:2 Combiner Ring: x4 CLEX 2 beams test area CALIFES Probe beam photo-injector Drive Beam Injector thermionic gun PHIN Drive beam photo-injector test stand UV laser beam DRIVE beamPROBE beam Electrons PHINCALIFES charge/bunch (nC) gate (ns) bunch spacing(ns)0.666 bunch length (ps)10 Rf reprate (GHz)1.5 number of bunches machine reprate (Hz)55 margine for the laser1.5 charge stability<0.25%<3% QE(%) of Cs2Te cathode30.3 Possible change over in next few years Machine parameters set the requirement for the laser Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Laser requirements 1.5 GHz Synched oscillator Cw pre- amplifier 10W Phase- coding test 3-pass amplifier 2-pass amplifier 3.5kW8.3kW7.8kW 14.8mJ in 1.2μs 2ω2ω 3.6kW 4.67mJ in 1.2μs 4ω4ω 1.25kW 1.5mJ in 1.2μs Feed- back stab. PARAMETERS PHINCALIFES Laser in UV laser wavelegth (nm)262 energy/micropulse on cathode (nJ)> energy/micropulse laserroom (nJ) energy/macrop. laserroom (uJ)9.8E+024.1E+01 mean power (kW) average power at cathode wavelength(W) E-04 micro/macropulse stability<0.25%<3% Laser in IR conversion efficiency energy/macropulse in IR (mJ) energy/micropulse in IR (uJ) mean power in IR (kW) average power on second harmonic (W)0.491.E-03 average power in final amplifier (W)915 Feed- back stab. Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Achieved Not available yet The laser was not designed for CALIFES parameters

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Results on PHIN Feedback stabilization Phase coding Laser for CLIC Future plans

Contributions Marta Csatari Divall Photonics Europe April 14, 2010 Stability of a high power diode-pumped Nd:YLF laser system for photo-injector applications at CERN 1.5 GHz Synched oscillator Cw pre- amplifier 10W Phase- coding test 3-pass amplifier 2-pass amplifier 3.5kW8.3kW7.8kW 14.8mJ in 1.2μs 2ω2ω 3.6kW 4.67mJ in 1.2μs 4ω4ω 1.25kW 1.5mJ in 1.2μs HighQ front end Cooling AMP1 head assembly AMP1 and AMP2 Phase-coding test Harmonics

Amplifiers AMP1AMP2 Pumping power15.5 kW18.8 kW Rod length x diameter 8cm x 0.7cm (7cm pumped) 12cm x 1cm (11cm pumped) Number of passes3 non-collinear2 collinear Small signal gain coeff. (1/cm) Steady-state gain Power output3.2 kW8.3 kW Extractable from pump 53%49% Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 NEW!

1047nm523nm262 nm RMS stab. (train) 0.23%0.8% (0.45%) 1.3% (1.6%) Energy/pulse (μJ) Pulse length (ps) 77~5ps Beamsize (μm X μm) 418 X X 224 Conversion efficiency (T=89% to harmonics) 47% (best 50%) 35% (best 47%) Crystal -KTP 11mmADP 0 C Harmonic stages Preliminary measurement on response to long train 1.2 μs 1 cm KDP 18% efficiency Flat response Beam size/ shape to be optimized Amp2 as in table Amp1 only X4 less intensity Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Phase coding Diagnostics/Results on PHIN Feedback stabilization Laser for CLIC

Laser diagnostics Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Distance from 4 th harmonic crystal (mm) Beam transport ~11m 71% to cathode PHIN Transmission is low for CALIFES line Pointing instabilities are high due to long distances Closer to the gun would be better Automated measurement system needed ~70m 64% to cathode under vacuum CALIFES

Current status on PHIN pointing Laser position/size Electron beam position/size Size (mm) Movement (mm) Size (mm) Movement (mm) xyδxδxδyδyxyδxδxδyδy best % % % % worst % % % % Taken with virtual cathode camera and OTR screen camera Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Current status on PHIN amplitude Amplitude stability Train length Laser energy (nJ) Current/ bunch (nC) (ns) best % RMS % RMS 1250 worst % 1 2.4% 1300 Macropulse stability IRGreenUV Measured (no sat. exp.) 0.23%0.8% (0.45%) 1.3% (1.6%) In PHIN Current: sigma =0.8 % In laser room Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Exceptional stability without feedback stabilization! Pointing instabilities can be improved by better airflow control Amplitude feedback system is necessary Thanks to PHIN team

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Results on PHIN Feedback stabilization Phase coding Laser for CLIC Future plans

Sources of instabilities AmplitudePointing Electrical noise/power supplier noise Pumping diodes Seed source (osc+preamp) Phase coding Pointing (amplification + harmonic stages) Thermal drifts Mechanical vibration Water cooling system Air conditioning (temperature variation+ airflow) Vibration Airflow in beam transport Lack of relay imaging Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Some also affecting the measurement system!

Sources of instabilities Improving the environment for the laser is necessary: Better temperature stabilization Less airflow, better enclosure (planned for May 2010) Move the laser closer to the gun Change to solid metal mirror UV train energy (mJ) RMS amplitude stability Reflectivity %69% 1: on small crack %87.4% 2: on reflective surface %43.7% 3: on big crack Mirror inside the gun Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Scheme to improve stability Could be reversed for feed forward option In TESLA this system was invented by I. Will and his group 0.7% rms stability was achieved from 3% with 70% transmission Similar system tested at RAL with 4 μs speed →0.25%RMS over 140 μs in the UV Commercial LASS-II by Conoptics at green wavelength 500kHz (Int. Ref. Mode) 100kHz Custom design for quasi-cw available EO modulators ordered for in house tests System specifications by spring 2011 HOW to measure? Development of a measurement system with >10 4 dynamic range is necessary Challenging task with the phase-coded short train More detailed fast noise measurements planned for 2010 Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Noise measured on PILOT system

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Results on PHIN Feedback stabilization Phase coding Laser for CLIC Future plans

Phase-coding Lens system Pockels cell waveplate Polarizer 5% 55% Losses in % T=38% waveplate 2% Full power train from amplifiers Polarizer 2% With type2 crystal we could get T=80% Alternative scheme Driver specification is very demanding (3.6MHz, fast rise time,high average power) Monitor latest status for available drivers on the market Slow switching demonstrated Recombination and delay measured Damage due to the high input power, only 10mW output RF driver is not up to our specification(see picture) Driver response to square input (voltage applied to modulator) Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Oscillator 320mW Fiber coupler EO modulator splitter 333ps delay Variable attenuator Fiber outcoupler 20% 82% 11% Losses in % EO modulator 11% waveplate 2% 20% 82% T=9% NEW scheme Components in purchasing Booster amplifier ordered in Feb/2010 Planned commissioning on PHIN autumn/2010 Booster amplifier 300mW

Laser driven photo-injector option ADVANTAGESTo demonstrate Proven capability to synchronize to external RF source Amplitude stability <0.25% RMS for PHIN <0.1% RMS for CLIC Flexibility for timing structure, single pulse operation Working phase-coding system Size, shape, pulselength, energy can be optimized for machine Reliable long term operation (~1000 hour running time during 2009 is already good) Can produce polarized electronsHigh charge Gives smaller transverse emittance No energy tails (from the laser) No satellites Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Outline Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Photo-injectors for CTF3 Current laser setup Results on PHIN Phase coding Feedback stabilization Lasers for CLIC Future plans

Lasers for CLIC Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Lack of laser time for research development on the laser Long train operation for CLIC (140 μs) High average power operation (100Hz) Stability and stabilization (Phase coding on the way independently from operation until installation on PHIN ~October 2010) Main challenges identified Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Modifications to the setup Using ‘leakage’ wherever we can No interruption to operation High repetition rate test are risky and still cannot be performed Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Laser design was for long trains of the CLIC drive beam CALIFES requires only up to 226 pulses (160ns) 1μJ in the UV is necessary for short train, which have not been delivered yet CALIFES will be used as a diagnostic test bench until 2015 at least ~60kEuro for replacing old parts The footprint is 60cm X 150 cm + the oscillator Deliverable by Spring 2011 In collaboration with IAP for amplification Rest of the system needs new oscillator For <1% change at the output the switch on time has to be <350ns accurate <1% variation over the train at nominal energy Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Independent laser system for CALIFES This is how long the CALIFES train is Allow the amplifier to store the energy before pulses arrive Higher energy can be reached Stability needs to be investigated PILOT laser tested on CTF2

500MHz front end and the existing amplifiers could be used for tests for CLIC With reprate tripling configuration PHIN could still be used as it is High repetition rate operation/fracture/thermal lensing to be studied Non steady-state operation and pre-pumping to be tested It would also be a useful source for cathode studies Commercial oscillator+ pre-amplifier+ harmonic stages is available (up to 30W in the IR ~15W in green without amplification) ~200kEuro 4 months from order 3 months for tender After proof of new configuration for CALIFES laser Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 New source for PHIN laser and CLIC

Current amplifiers in a pre-pumped mode with a pre-shaped pulse Pre-shaped input pulse After 1st amplifier After 2 nd amplifier By Mikhail Martyanov from IAP ~20kEuro 3-4 months development for driver electronics 5 weeks testing In collaboration with IAP Stability can be an issue 1 year for tender for diodes/drivers and chiller With original design 600kEuro STFC doing feasibility for SLAB geometry Steady state operation with an additional amplifier We are working well above saturation fluence We are close to fracture limit Slab amplifier might be better solution Further feasibility is required in 2010/2011 Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3 Feasibility for CLIC laser

Future plans 2010 Detailed noise measurements (laser and PHIN) Improved laser environment by autumn Implementation and test of phase-coding 2011 Implementation and test of feedback stabilization system Noise measurements on the machine Long train harmonics stages Design studies for CLIC laser Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Thanks for all, who contributed ! CTF3 Collaboration meeting 6 th May 2010

Harmonic stages 50% conversion efficiency KDP-I, 82  4 th harm. efficiency 10 mm mm mm0.21 ADP-I,90  20mm % conversion efficiency Mikhail Martyanov, Grigory Luchinin, Vladimir Lozhkarev IAP G. CHEYMOL- M. GILBERT CEA bypass for PHIN Pulse Picker Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Response time of the amplifier will depend on the gain and the relaxation time and output fluence Fast input variations will not be damped Noise response Effect of 100 kHz seed modulation on the output (PILOT laser 2004 ) Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Oscillator and preamp from HighQ < 0.2 % rms above the 100 kHz noise region <1% rms below the 100kHz noise region Pumping diodes Current overshoot <1% Ripples <1% Temperature The best technology for the time was bought We are more sensitive to pump variation Stabilized diode technology should be investigated 0.33% RMS stability is measured in the IR How is the output power affected by the input parameters? Steady-state MOPA Interlinked with all the others Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Photo-injectors around the world Marta Csatari Divall CTF3 Collaboration meeting 6 th May 2010Photo-injector laser for CTF3

Long train test bench Using the rejected beam after 1 st Pockels-cell This would allow us to do independent tests during CALIFES operation Long train studies on the harmonic stages should be done with existing amplifiers Feedback stabilization and stability measurements could be carried out at different wavelengths ~30kEuro for hardware 2-3 months for stability measurements (starting summer 2010) Specification of feedback stabilization system (by end of 2010) 4-6 weeks harmonics studies and fracture limit test (September 2010) 2-3 months crystal temperature stabilizer development 2 months feedback stabilization with new electronics (by spring 2011) Starting summer 2010