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

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

3. 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

4. 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

5. SPARC gun design

6. Gun and solenoid installed

7. Gun and emittance meter installed

8. 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

9. 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.

10. LNF RF measurements
0 mode
p mode

11. LNF Measurements (cont)
Atmospheric pressure nitrogen n =
Df = KHz
Anticipated operating temperature 36 °C

12. 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.

13. Octoyoke (design)

14. 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.

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

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

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

18. 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.