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SPARC RF gun status

This article provides an overview of the SPARC photoinjector RF gun's current status, improvements, and measurements conducted at LNF and UCLA. It discusses the gun's redesign, UCLA measurements, gun accessories, and octoyoke improvements. The near future plans include vacuum testing, finalizing magnetic measurements, and installation in the SPARC hall.

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SPARC RF gun status

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  1. SPARC RF gun status by P. Musumeci Review committee 14/06/2005 Frascati

  2. Outline • SPARC photoinjector • RF gun • UCLA measurements • Status at LNF • Magnetic solenoid • UCLA measurements • Status at LNF • (Near) future plans

  3. Acknowledgements • Thanks to F. Tazzioli, A. Battisti, and in general everybody at LNF… • Collaboration with UCLA team

  4. Photoinjector specifications The goal is to achieve ultra-high beam brightness to drive efficiently the SASE-FEL • Ferrario working point • Laser pulse shaping • Beam emittance detailed study

  5. 1.6 cell RF Gun • S-band SLAC/UCLA/BNL design • Many of its kind in high brightness beam laboratories around the world • Baseline design for LCLS

  6. SPARC photoinjector (design)

  7. SPARC photoinjectorat LNF

  8. SPARC RF gun improvements • Gun Redesign • SLAC ORION gun (same design) run without tuners at > 15 MW • Very little breakdown • Resulted in “diffusion bonding” of cathode to gun cell wall • Prevented by application of TiN to cathode perimeter • Improved alignment/support • 3-D model constructed with HFSS

  9. UCLA measurements • Tune Field Balance • Bead pull and bead drop techniques • Cathode, tuners, temperature • Gun Mode Characteristics • Higher Q - tuners out of circuit • Mode separation reproducible after cathode replacement • Full Cell Coupling Loop • Agreement between waveguide forward and full cell monitor power levels • Differential expansion changes calibration - RF test should be performed at running temperature to recalibrate full cell probe

  10. UCLA measurements (cont.)

  11. Gun Accessories • Gun chiller • Gun temperature independent from other accelerating cavities • Remotely controllable. • Measured water flow up to 5 l/min sufficient to guarantee stable operation at 10 Hz full power. • Support • Fully adjustable in 6 degrees of freedom: x,y,z pitch, yaw, and roll. • Solenoid independently adjustable • Ample longitudinal movement with slits for gun servicing / cathode replacement. • Bolts and nuts all in order at the end of May.

  12. RF Gun at Frascati • Gun + octoyoke arrived in February this year • Support built & assembled • Tuners installed • Laser windows installed • Water circuit tested

  13. p mode 0 mode LNF RF measurements • Nitrogen flow • Hook up a network analyzer • Possibility of measuring RF gun parameters vs. temperature • Preliminary measurements of the coupling confirm UCLA results

  14. LNF Measurements (cont) • Atmospheric pressure nitrogen n = 1.0003 • Df = + 850 KHz • Anticipated operating temperature 36 °C

  15. Octoyoke • Magnetic solenoid for emittance compensation • Solenoid Redesign • Adjustable four coil design with field stiffening inserts • New coil design - improved cooling • Maximum current now 300 A (previously 220 A) • 3-D model constructed with RADIA • Asymmetric excitation of coils researched to study lens center variation

  16. Octoyoke (design)

  17. (a) (b) (c) Magnetic lens center control To be optimized in SPARC initial phase emittance measurements

  18. UCLA measurements Good agreement with three dimensional simulations 4 coils excitation 2 coils excitation I = 150 Amp. Residual field on the cathode < 7 gauss

  19. Octoyoke at LNF • Strengthen the rods • Holes for alignment tool • Magnetic axis definition • Temperature and electrical characterization • Three dimensional magnetic map underway

  20. Photoinjector near future • Vacuum test • Repeat RF measurements with proper waveguide launcher • Finalize magnetic measurements of solenoid • Installation in SPARC hall

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