1. CLIC DB injector facility, photo-injector option studies LCWS, Granada, September 26 th -30 th,2011Steffen Döbert, BE-RF  CLIC DB injector  Thermionic gun baseline  Photo-injector option  Conclusions S. Bettoni, A. Vivoli, O. Mete, R. Corsini, A. Andersson, M. Csatari, H. Shaker

2. Objectives  Get started with some CLIC equipment for the drive beam  Develop 1 GHz rf system, klystron, rf structure challenging, long lead time, cost driver  Construct high average current particle source  Demonstrate long pulse operation within the stability specification  First part of CLIC 0

3. CLIC DB injector specifications ParameterNominal valueUnit Beam Energy50MeV Pulse Length140.3 / 243.7  s / ns Beam current4.2A Bunch charge8.4nC Number of bunches70128 Total charge per pulse590 CC Bunch spacing1.992ns Emittance at 50 MeV100mm mrad Repetition rate100Hz Energy spread at 50 Mev1% FWHM Bunch length at 50 MeV3mm rms Charge variation shot to shot0.1% Charge flatness on flat top0.1% Allowed satellite charge< 7% Allowed switching time5ns

4. Phase coding 180  phase switch Acceleration 0 Deflection 0 / 2 Sub-harmonic bunching 0 / 2 CTF3 example Phase coding by sub-harmonic bunching

5. Satellites bunch population estimated to ~8 %. Satellites High bandwidth buncher and rf source needed Phase switch: Phase switch within eight 1.5 GHz periods (<6 ns).

6. P REBUNCHER B UNCHER S LIT A CCELERATING CAVITY 53 MeV 6 MeV 26 MeV SHB S OLENOIDS CLIC DB injector schematics T HERMIONIC GUN Documented in the CDR; a scaled version of CTF3

7. Simulation results Longitudinal phase space after sub-harmonic bunching Same total gap-voltage but fewer cells (2 instead of 6) 35-39 KV needed

8. Accelerating cavities parameterUnitValue Phase velocity Number of cells Phase advance per cell Total length Voltage Beam aperture radius c  m MV cm 1 10 2/3 0.9998 4.8 4.7 Simulation results Exit of the solenoids at around 26 MeV, Satellites and tails visible

9. B EFORE THE CHICANE A FTER THE CHICANE Simulation results Longitudinal phase space after the cleaning chicane, 24 % intensity loss at the chicane

10. ParameterUnitSimulationsCLIC Energy Bunch charge Bunch length (rms) Energy spread (rms) Horizontal normalized emittance (rms) Vertical normalized emittance (rms) Satellites population MeV nC mm MeV  m rad % 53.2 8.16 2.83 0.45 (@53 MeV) 32.9 28.7 4.9 8.4 3 (@ 50 MeV) < 0.50 (@ 50 MeV)  100 As small as possible Simulation results  Specifications can be fulfilled  Some ideas to improve the satellites and total losses  Beam loading and wake field effects to be studied  Real rf-design of buncher needed

11. Thermionic gun CTF3: 1.6  s, 9.6  C per pulse 1 % droop specs  7 nF, ~70 J stored energy CLIC: 140  s, 700  C per pulse 0.1 % droop specs  5  F, ~50 kJ stored energy grided cathode might not survive CTF3 gun concept might be not scalable for CLIC Some simple considerations  Most likely new gun design needed, potential candidate would be a klystron type gun with grid and a HV modulator Does anybody has experience with such an approach ?

12. Photo injector option Advantages No satellites or tails, phase coding on the laser side No or less bunching needed, possibly better emittance Flexible time structure Concerns Cathode lifetime Challenging laser, peak and average power Intensity stability Maintenance and operation

13. Phase coding 333ps switch 999ps switch

14. Charge production Showed in CTF2 already the bunch charge needed (> 10 nC) Total charge test performed in the cathode lab (> 1 mC) 460 h with 1.5% QE have been shown in excellent vacuum Combination of those together has not yet been demonstrated Cathode lifetime under this rough conditions is a big concern Charge production with PHIN

15. Stability Laser RMS Current RMS Train length(ns) 1.3% RMS 0.8% RMS 1250 best 2.6%2.4%1300 worst MacropIRGreenUV RMS stability 0.23%0.8%1.3% We need 0.1% RMS stability In PHINIn laser room Nonlinear conversion increases noise and causes amplitude variations along the train Beam stability seems almost entirely determined by laser stability First tests of feedback system is encouraging

16. Beam dynamics simulations Using scaled version of PHIN gun, 1 GHz Concerns: Power, cooling and vacuum

17. Comparison simulation results

18. Working packages and plans WP: CLIC Drive Beam Injector 2012-2016  Detailed technical design of the injector  Thermionic gun, design and construction  RF-structures (buncher + accelerating structure), design and construction  1 GHz and 500 MHz high power system (Klystron, Modulator, waveguide system)  LLRF system  Magnets, solenoids, quadrupoles, dipoles, correctors  Vacuum system including collimators  Diagnostics (high current, long pulse, very good resolution)  Controls  Commissioning and operation

19. Work package Photo injector option 2012-2016  Continue working with PHIN set up, study increased bunch charge and cathode lifetime issues  Laser Intensity feedback  Try to generate CLIC-like laser pulses to study average power and train stability issues  Eventually design and realize 1 GHz rf-gun  Full system test (1 GHz rf system needed)  Some work on alternative (green) cathodes

20. Conclusions  Conceptual designs for both injector options exist, more detailed technical design has to start  Will continue following up the photo injector option  Try to design test facility which allows to test both  Have to start with thermionic gun and 1 GHz system as soon as possible !  Presented conceptual design for thermionic injector is going to be studied together with rf structures needed for bunching

21. Transverse dynamics Transverse optics after the solenoids at 26 MeV