SPARC RF gun status by P Musumeci Review

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

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

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

Photoinjector specifications RF Gun Peak electric field at cathode [MV/m] 120 Peak RF power [MW] at 120 MV/m 14 RF frequency [MHz] 2856 Cathode material Cu, Mg Solenoid Magnetic field maximum [T] 0. 31 Effective length [cm] 20 Maximum coil current [A] 300 • Ferrario working point • Laser pulse shaping • Beam emittance detailed study The goal is to achieve ultrahigh beam brightness to drive efficiently the SASE-FEL

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

SPARC photoinjector (design)

SPARC photoinjector at LNF

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 Ti. N to cathode perimeter – Improved alignment/support – 3 -D model constructed with HFSS

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

UCLA measurements (cont. ) Mode separation (0 -p) for balanced field 3. 06 MHz Coupling b (also VSWR) 1. 22 Q 0 12500 Reflected power 1% Anticipated running temperature 40 °C Full cell coupling calibration -65. 4 d. B

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.

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

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 p mode 0 mode

LNF Measurements (cont) • • • Atmospheric pressure nitrogen n = 1. 0003 Df = + 850 KHz Anticipated operating temperature 36 °C

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

Octoyoke (design)

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

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

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

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