The Fermilab Photo-Injector Jean-Paul Carneiro (Fermilab & Université Paris XI)

The Fermilab Photo-Injector Jean-Paul Carneiro (Fermilab & Université Paris XI) www.phwiki.com

The Fermilab Photo-Injector Jean-Paul Carneiro (Fermilab & Université Paris XI)

Haughton, Natalie, Food Editor has reference to this Academic Journal, PHwiki organized this Journal The Fermilab Photo-Injector Jean-Paul Carneiro (Fermilab & Université Paris XI) For the A0 group (N. Barov, M. Champion, D. Edwards, H. Edwards, J. Fuerst, W. Hartung, M. Kuchnir, J. Santucci) Accelerator Physics in addition to Technology Seminars Fermilab, March 23, 2001 R&D on linear colliders e+/e- at Fermilab

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THE TESLA ACCELERATOR 9-cells superconducting cavities Must achieve 40 MV/m to get 0.8 TeV COM. Today ~ 33 MV/m. To develop the technology of TESLA: installation at DESY (Hamburg) of a TESLA TEST FACILITY accelerator. THE TESLA TEST FACILITY ACCELERATOR ~ 100 meters Fermilab contribution to TTF : – design, fabrication in addition to commissioning of the TTF injector (Nov 98). – design in addition to prototyping of RF couplers as long as the cavities. – design in addition to prototyping of long-pulse modulators as long as the klystrons. THE TESLA TEST FACILITY ACCELERATOR

THE TESLA TEST FACILITY PHOTO-INJECTOR Self-Amplified Spontaneous Emission observed at 209 nm in February 2000. Concept of Photo-Injector gun: Photo-cathode

TTF INJECTOR BEAM PARAMETERS Quantity Charge per bunch Bunch spacing Bunches per RF pulse Repetition rate TTF spec. 1-8 nC 1 µs 800 10 Hz Quantity Energy Transverse emittance at 1 nC Transverse emittance at 8 nC TTF spec. 20 MeV 2-3 mm-mrad 15 mm-mrad A0 PHOTO-INJECTOR LAYOUT (First beam the 3rd of March 1999) Oscillator Nd:YLF 81.25 MHz 2 km optic fiber Pockels Cell 1 MHz Multi-pass amplifier Nd-glass Double-pass amplifier Nd-glass 12 nJ/pulse 60 ps 1054 nm 2.5 nJ/pulse 400 ps 800 pulses 2 nJ/pulse 400 ps 100 µJ/pulse 400 ps 0.8 mJ/pulse 400 ps 600 µJ/pulse 400 ps 400 µJ/pulse 4.2 ps 100 µJ/pulse 4.2 ps 532 nm 20 µJ/pulse 4.2 ps 263 nm 10 µJ/pulse 10.8 ps 263 nm LASER (University of Rochester) STACKED UNSTACKED Spatial filter Compressor BBO Crystals Pulse stacker

UNSTACKED LASER PULSE 4.2 ps FWHM / 20 µJ STACKED LASER PULSE 10.8 ps FWHM / 10 µJ The two regimes of the A0 laser system : THE PHOTO-CATHODE PREPARATION CHAMBER (INFN-Milano) Coat Mo cathodes with a layer of Cs2Te, a material of high quantum efficiency (QE). Use manipulator arms to transfer the cathode from the preparation chamber into the RF gun while remaining in UHV. Cathodes must remain in ultra-high vacuum (UHV) as long as its entire useful life, because residual gases degrade the QE. Contamination can be reversed by rejuvenation: heat cathode to ~230 C as long as some minutes. The same cathode has been used in the RF gun as long as ~2 years without degradation of its QE (~0.5-3%) BUCKING SOLENOID PRIMARY SOLENOID SECONDARY SOLENOID THE RF GUN AND SOLENOIDS (Fermilab & UCLA) RF gun in addition to solenoids developed by Fermilab in addition to UCLA. Mode Resonant frequency Peak field Total energy Peak power dissipation Pulse length Repetition rate Average power dissipation Cooling water flow rate TM010, 4.5 MeV 2.2 MW 800 µs 10 Hz 28 kW 35 MV/m 4 L/s Q 24000 1.3 GHz Gun parameters Solenoids parameters Bucking & Primary max. Bz -> 2059 G (385A) Secondary max. Bz -> 806 G (312 A) 1.5-cell copper cavity designed as long as a high duty cycle (0.8%). RF GUN

THE CAPTURE CAVITY (DESY & SACLAY/ORSAY) & THE CHICANE (Fermilab) CHICANE CAPTURE CAVITY Capture cavity parameters Chicane parameters 9-cell L-b in addition to superconducting cavity of TTF type. Operated daily at 12 MV/m on axis. 4 dipoles of equal strengths, 2 with trapezoid poles in addition to 2 with parallelogram poles. Operated @ 2A, ~700 Gauss. Bend in the vertical plane Compression ratio ~5 – 6 (theory in addition to measurements) THE LOW BETA SECTION THE WHOLE BEAMLINE SPECTROMETER EXPERIMENT PLASMA WAKEFIELD ACCELERATION DARK CURRENT STUDIES Dark current measurement principle : Using a Faraday Cup at X2 (z~0.6 m). Bucking Ib Primary Ip Secondary Is

Comparison of Dark current : March 99 / November 00 Edge of the photo-cathode Edge of the photo-cathode Where does the dark current come from Probably the surface of the photo-cathode. Photo-cathode & back of the RF gun Dark current spots & photo-current in X6 (z=6.5 m) Round beam Flat beam Effect of the solenoids settings on the dark current

Effect of the vacuum on the dark current QUANTUM EFFICIENCY STUDIES Round beam Flat beam Effect of the solenoids settings on the Quantum Efficiency

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Charge Vs. Laser Energy as long as 2 longitudinal sizes of the laser beam on the photo-cathode. Charge Vs. Laser Energy as long as 3 different transverse sizes of the laser beam on the photo-cathode. Charge Vs. Laser Energy as long as = 0.8 mm on the photo-cathode. (Hartman, NIM A340, p.219-230, 1994)

TRANSVERSE EMITTANCE MEASUREMENTS Laser RF Gun Capture Cavity The photo-injector is a set of 8 parameters: Goal: find as long as a charge Q, the set of parameters that gives the min. transverse emittance. Remark: as long as all the emittance measurements, the chicane was OFF in addition to DEGAUSSED. How do we measure the transverse emittance at A0: using slits Slits width: 50 µm Slits spacing: 1mm Location of the emittance slits ~ 3.8 m ~ 9.5 m ~ 6.5 m

FLAT BEAMS IMAGES (Q=1 nC) Be as long as e compression Laser pulse length Laser transverse size on cathode Launch phase Peak field on RF gun Accelerating field on capture cavity Transverse normalized RMS emittance Energy spread Bunch length Peak current After compression Transverse normalized RMS emittance Bunch length Peak current Q = 1 nC Q = 8 nC Prediction Measurement Prediction Measurement 13.5 ps 10.8 ps 28 ps 10.8 ps 0.7 mm 0.8 mm 1.5 mm 1.6 mm 35 deg 40 deg 45 deg 40 deg 50 MV/m 40 MV/m 50 MV/m 40 MV/m 15 MV/m 12 MV/m 15 MV/m 12 MV/m 2.5 mm-mrad 0.16% 1.27 mm 80 A 3.02 mm-mrad 1 mm 120 A 3.7 ± 0.1 mm-mrad 0.25 ± 0.02 % 1.6 ± 0.1 mm 75 A non-measured non-measured 0.55 ± 0.07 mm 218 A 1.2 % 3.1 mm 386 A 15 mm-mrad 19.4 mm-mrad 1 mm 958 A 0.55 ± 0.05 mm 1741 A 330 A 2.9 ± 0.2 mm 12.6 ± 0.4 mm-mrad 0.38 ± 0.02% Comparison Prediction (Parmela, 1994) in addition to Measurements (1999->2001) CONCLUSIONS CONCLUSIONS (continued) The Photo-Injector designed by Fermilab meets its specifications. Possible future studies of the photo-injector: – Underst in addition to the dark current source. – Underst in addition to the dark current in addition to QE “zig-zag” as a function of time as long as round beam in addition to flat beam settings. – Measure emittance of a non-compressed beam using 20 ps FWHM laser pulse to see if we can decrease the emittance further. – Measure the transverse emittance of a compressed beam to study the predicted emittance increase in the deflection plan (as CERN studies). – Pursue the user experiments.

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