Drive Beam Generation in CTF3 S. Bettoni (CERN) for the CTF3 commissioning team

1. Talk outline • Drive beam manipulation: • Combiner ring (factor 4) • Delay loop (factor 2) • Delay loop AND combiner ring (factor 8) • Beam delivery to CLEX • Conclusions Drive Beam Generation in CTF3 S. Bettoni (CERN) for the CTF3 commissioning team

2. structures 12 GHz PETS on-off deceleration stability two-beam acceleration structures 30 GHz CTF3 for CLIC • CTF3 is a small scale version of the CLIC drive beam complex: • Provide the RF power to test the CLIC accelerating structures and components • Full beam-loading accelerator operation • Electron beam pulse compression and frequency multiplication • Safe and stable beam deceleration and power extraction • High power two beam acceleration scheme recombination x 4 recombination x 2 bunch length control bunch compression fully loaded acceleration phase-coding Structures Structure materials Drive Beam generation PETS on-off DB decelerator CLIC sub-unit

3. RF pulse without beam RF pulse with beam Analog signal Achievements in the past • The status of the machine up to CLIC08: • Provide the RF power to test the CLIC accelerating structures and components (since 2005) • Full beam-loading accelerator operation (since 2004) • Electron beam pulse compression and frequency multiplication (since 2006) Beam routinely sent during the week-ends to the PETS structures Measured RF to beam efficiency: 95.3 % Expected from the theory: 96% MKS05 MKS03 MKS06 * MKS07 To the rings To the 30 GHz test stand *After the cure of the vertical instability in the RF deflector, D. Alesini (LNF) et al.

4. CTF3 operation scenarios

5. Delay loop: the recombination 2007

6. Delay loop: improvement of the recombination The first phase switch introduces different loading ONGOING Put a couple of 180º phase switches in the transient part of the train

7. Delay loop: current stability

8. Delay loop: control of the optics By-passing DL Through DL • Delay loop optics: • Control of the optics enough to have successful recombination (betas and dispersion) • Small adjustments (order of %) necessary to have full transmission (worse for the model): • Identified regions of model/machine discrepancies by means of kick measurements • The optics is quite transparent for the beam

9. Combiner ring: the recombination 2008

10. Combiner ring: current stability

11. Combiner ring: control of the optics • To validate the MAD-X model of the combiner ring: • High precision kick measurements compared to the model predictions: • Symmetric kick analysis to identify single quadrupole error • Multi-turn analysis to magnify the effect of the discrepancy • Other independent measurements are used to check the correction: • Dispersion • Tunes TURN 1 TURN 2 TURN 3 P. Skowronski

12. Now Achievements in the past • The status of the machine up to CLIC08: • Provide the RF power to test the CLIC accelerating structures and components (since 2005) • Full beam-loading accelerator operation (since 2004) • Electron beam pulse compression and frequency multiplication (2006-present) • The status of the machine up to CLIC08: • Provide the RF power to test the CLIC accelerating structures and components (since 2005) • Full beam-loading accelerator operation (since 2004) • Electron beam pulse compression and frequency multiplication (2009)

13. Delay loop & combiner ring: THE recombination ONLY DL DL & CR ONLY CR

14. New lines installed in 2008/2009 • New lines installed: • TL2 → transfer line from CR to the CLEX area • CLEX area: • TBL → study the drive beam stability during the deceleration • TBTS → test the two-beam acceleration scheme • CALIFES → probe beam linac RRCAT • Module-3 • Tunable R56 (from -0.35 to +0.35) • Achromatic arc • Final matching doublet • Module-2 • Straight section for tail clipper • Vertical achromat • Matching section • Module-1 • Horizontal achromat

15. Going to CLEX 3x 4x Twiss parameters for the different extracted turns quite similar

16. Transfer line 2: control of the optics • Steps of the commissioning: • New MTV monitor installed in the line during the 2008/2009 winter shut down • Commissioning made more difficult by the BPM not working properly yet (work in progress) • Uncombined beam transported almost to the end of the line, combined with more losses • Kick measurements evidenced two regions where the model and the machine don’t agree (check on the two identified quadrupoles this week) Uncombined beam CR CR combined beam TL2

17. The control of the orbit • In CTF3 the control of the orbit is more critical than in other machines: • The efficiency of the recombination depends on the ring length • The subpulses which go through the DL must be put on top of the ones which go straight • The orbit of the recombined subpulses in the CR is the superposition of more orbits • The closure of the orbit in the CR is crucial also for the transport of the recombined beam • Input: • Maximum tolerance • Maximum strength of the correctors • Response matrix measured or from the model (CR) ONGOING • Input: • Maximum tolerance on: • The orbit difference • The overall orbit excursion • Maximum strength of the correctors measured

18. CTF3 reliability • Fully loaded operation mode + RF compression don’t make CTF3 reliable “for free”: • Orbit references (Indian collaboration) • RF loading and beam current references (tool to do it automatically to be tested) • Phase loop (A. Dubrovskiy, CERN)

19. Conclusions • SEVERAL OF THE CTF3 GOALS HAVE BEEN ALREADY DEMOSTRATED IN THE PAST YEARS: • Fully loading operation mode (consistent with theory predictions) • First demonstration in delay loop • 2009 MILESTONES: • Successful factor 4 recombination achieved • Successful factor 2 recombination in delay loop obtained • Factor 2x4 recombination putting in operation delay loop AND combiner ring • Beam through PETS in the CLEX area • FUTURE SHORT TERM PROGRAMS: • Improve the reliability and the stability of the machine • Further optics studies in the delay loop and in the new lines • Test of the two beam acceleration scheme in CLEX (acceleration and stability studies)

20. SPARE SLIDES

21. Measurements in TL2 CC.QDH0220 = -23 % CC.QFL0530 = +20 %

22. Streak camera image satellite main 1 8 666 ps Delay loop: fast phase switch & satellites Fast phase switch from SHB system

23. Phase coding How to “code” the sub-pulses Sub-Harmonic Bunching n0 / 2 Combination scheme 180 phase switch Acceleration n0 Deflection n0 / 2 even buckets • Delay Loop odd buckets • RF deflector Gap creation and x2 multiplication Ldelay = nl0 = c Tsub-pulse

24. injection line 1st turn 2nd septum 1st deflector 2nd deflector local inner orbits lo RF deflector field 4rd 3rd lo/4 Combiner ring multiplication

25. Gacc unloaded Transient DP/P (%) -5 0 5 Lstruct Steady state loaded Time resolved beam energy spectrum measurement in CTF3 s 100 200 300 400 Time (ns) Ebeam E0  E0 /2 steady state tfill t Fully loaded operation mode

26. THE recombination: current stability FIRST MEASUREMENT (NOT BEST CONDITIONS)

27. THE END