ELYSE An Intense Electron Linac for Pulsed Radiolysis Research T. Garvey, M. Bernard, H. Borie, J.C. Bourdon, B. Jacquemard, B. Leblond, P. Lepercq, M. Omeich, M. Roch, J. Rodier, R. Roux Laboratoire de l Accélérateur Linéaire, Orsay. F. Gobert, H. Monard, Laboratoire de Chimie-Physique, Orsay. Conseil Régional d'ile de France Essonne
The ELYSE project CENTRE DE CINETIQUE RAPIDE Photol ys Radiol ys LASER - femtosecond ACCELERATOR - picosecond S.E.R.A.
T. Garvey, EPAC 2002 Accelerator Specifications _ Energy 4 9 MeV _ Bunch charge 1 nc * _ pulse duration 5 ps (FWHM) _ I peak ~ 200 A 2 ka _ Energy spread 2.5% (RMS) _ Normalised emittance 60 mm-mrad (RMS) _ Beam size on target 2 20 mm diameter _ Repetition frequency 10 100 Hz 10 nc would be desirable!
PIQ12 PIQ16 PIQ21 JVS WCM1 TR1-1 PIQ27 D1 ELM laser PIQ33 WCM2 TR1 19 mars 2002 CPC SOL ExLM HV1 H2 V2 TR1-2 H3 FAC1 TR2 VA Q2 Scale. 1/20e valve vacuum pump quadrupole dipole WCM HV H V CFA RGA steering CV JVS CV RGA : Residual Gaz Analysis WCM : Wall Current Monitor ELM : Entrance Laser Miror ExLM : Exit Laser Miror HA : Horizontal Slit VA : Vertical Slit FAC : FAraday Cup SC : Screen KOV : cerenkov radiator CPC : Cathode Preparation Chamber VC : Virtual Cathode VGB : Vacuum Gauge Booster V3 HA V4 WCM3 H4 V5 TR2-2 D2 WCM4 PIQ53 FAC2 TR2-1 PIQ63 WCM5 MEL FH MSL ECR - KOV ELYSE accelerator setup FAC3 TR3
Longitudinal Bunch Compression (H. Monard) _ Accelerate bunch off-crest of RF wave _ generate correlated phase-energy spread _ energy dependant path lengths in dipoles allow tail to catch up with head _ longitudinal compression - l = R 56 δe/e M. Uesaka et. al., Nucl. Inst and Meth. A 406, pp 371-379 (1988) Simulations show : bunch compression can compensate for lengthening due to space charge effects. Tests foreseen using streak photography of Cerenkov radiation from the beam
Simulations pulse duration gaussian 1,00 1,05 2,40 1,15 1,40 1,44 3,33 C S RMS pulse length (ps) 2,82 4,60 6,04 8,50 9 MeV 1 nc 10 nc 4 MeV 1 nc 2 nc 0,75 2,50 5,00 8,00 PARMELA simulations
Choice of Photocathode Want (i) long life-time (~ 50 hours) (ii) high quantum efficiency Q ~ E L. η For E L ~ 10 µj and Q = 10 nc need 1% _ need Cs 2 Te photo-cathode _ high vacuum requirements _ relatively easy fabrication _ Photo-cathode preparation chamber (cf. CTF, TTF) (c.f. Brookhaven project LEAF; large E L and metallic cathode)
T. Garvey, EPAC 2002
800 nm Photolysis Radiolysis R.F. gun Autocorrélator 3 ω 266 nm 2 ps - 70 µj 10-50 Hz ~ 15 m of transport 800 nm 120 fs 10 µj 950 Hz 800 nm 120 fs 2 ps Compression 800 nm 800 nm 120 fs 2 nj 80 MHz Amplifcator Ti:Saphire Tsunami Oscillator 650 mw Ti:Saphire Caméra CCD Spitfire 200 ps 532 nm 527 nm laser 1064 nm 4 W Nd:YVO 4 Merlin laser Q-switch 1054 nm 1 khz 10 mj - 10 W Nd:YLF lamp Kr femtoscope Millenia V Accélérator 3 GHz x 38 Quartz Pilot 80 MHz ELYSE - LASER
T. Garvey, EPAC 2002 Image of laser beam on an optically Equivalent Plane to that of the photocathode plane.
Amplifier PEK 19 mars 2002 SF6 PIQ-SHF PIK PRK POWER SUPPLY MODULATOR KLYSTRON ISOLATOR SPLITTER SF6 pressure PHASE SHIFTER LOAD PIG PRG PIS PRS ATTENUATOR H.F. of ELYSE accelerator PIQ12 GUN PML1G PML2G PMLB PIQ16 BOOSTER fenítre Vide-SF6 pumping tee vacuum pump coupler P = Power E = Entrance I = Incident K = Klystron G = Gun S = Section ML = Measure Loop
View of the ELYSE Accelerator
First photo-electron beam from the ELYSE Accelerator
EPAC 2002 Image of beam on screen at Experimental Area 1 Dark current Dark current + Photo current
45 40 35 Dark Current (ma) 30 25 20 15 10 5 0 1 1,5 2 2,5 3 3,5 4 4,5 RF GUN Power (MW)
EPAC 2002 Dispersed beam width at the analysing slit (slit width = 10 mm) Ibeam (mv) 800 700 600 500 400 300 200 100-30 -25-20 -15-10 -5 0 5 10 15 20 25 30 slit position (mm) Width at half height 55 mm 0.50 0.45 Ibeam (V) 0.40 0.35 0.30 0.25 0.20 0.15 0.10 2.15 2.20 2.25 2.30 2.35 E (MeV) 2.40 2.45 2.50 2.55 E/E @ half height = 12% x ~ [ρ(1- cosθ) + 2 L tan(θ/2)] E/E ~ 62 mm
Cathode surface showing signs of damage
Conclusions ELYSE has produced its first photo-electron beam _ (albeit with a copper cathode). First tests with a Cs 2 Te cathode will be performed soon. Excessive dark current levels need further studies. Considerable work remains to be done for machine optimisation - relative phases between laser and rf - optics settings. Note: Such guns exist today for the physical chemistry community thanks to investment in R&D programs for HEP (linear colliders), e.g. CTF.
Acknowledgements LURE Personnel M. Corlier and J. Vétéran magnet tests and measurements M. Begard and P. Corona magnet power supplies J.C. Frank and M. Geeraert radiation safety P. Robert cooling system LAL technical support G. Arnaud, F. Blot, J.N. Cayla, V. Chaumat, F. Cordillot, J. Lamouroux. Thanks to R. Bossart, J.C. Godot, K. Hubner, G. Suberluqc (CERN)