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

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

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

4. 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

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 photoinjector at 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 Gun Mode Characteristics
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.)
Mode separation (0-p) for balanced field
3.06 MHz
Coupling b (also VSWR)
1.22 Q0
12500
Reflected power 1%
Anticipated running temperature
40 °C
Full cell coupling calibration
-65.4 dB

11. 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.
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. 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
0 mode
p mode

14. LNF Measurements (cont)
Atmospheric pressure nitrogen n =
Df = 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. Magnetic lens center control
(b)
(c)
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