by P. Musumeci and F.Tazzioli SPARC RF gun status by P. Musumeci and F.Tazzioli Review committee 16/11/2005 Frascati

status Gun + solenoid +emittance-meter installed Vacuum pumps connected. Temperature control system connected Baking in preparation RF connection ready (see R. Boni’s report)

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 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

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 with relevant recent modifications

SPARC gun design

Gun and solenoid installed

Gun and emittance meter installed

Gun characteristics Mode separation (0-p) for balanced field 3.06 MHz Coupling b (also VSWR) 1.22 Q0 12500 Reflected power 1% Anticipated running temperature 36 °C Full cell field probe calibration -65.4 dB

Gun Accessories Gun chiller Support 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.

LNF RF measurements 0 mode p mode

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

Emittance compensation solenoid New design with four separately powered coils allows adjustment of lens center axial position. New coil design - improved cooling. Maximum current now 300 A (previously 220 A) Independently adjustable supports for gun and solenoid.

Octoyoke (design)

Work on Octoyoke at LNF Fixing rods of Yoke plates strenghtened Holes for alignment tool Magnetic axis definition Temperature and electrical characterization 3 D magnetic field map done at LNF has evidenced quadrupolar components.

Magnetic lens center control (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

Photoinjector near future Vacuum test and baking RF power conditioning ( two weeks) Laser beam on cathode Laser cleaning to optimize QE.

Outlook on gun improvements News from Erice October 05 PAHBEB workshop, from SLAC-GTF and BNL experience. Full cell tuning plungers favor RF arcing, therefore useless. New full cell tuning mechanism by deformation. 3 MHz separation of 0 and π mode insufficient. Transient excitation of 0 -mode causes large anomalous correlated energy spread. Better 15 MHz separation. Cleaning of Cu cathode with ion beams or plasma is effective and less perturbing than laser cleaning. Polished bulk Mg cathode proven with 10 MW RF power (100 MV/m). Research on Mg films at LNF. New design of solenoid to minimize quadrupolar field component. Note: The gun for LCLS is being redesigned with double symmetrical RF power feeding ports, tuning of full cell by deformation and large mode separation.