1. 3.9 GHz Harmonic Linearizer Elvin Harms LCLS-II Accelerator Physics Meeting 9 April 2014

2. Introduction 2 ACC39 at FLASH Proposal for LCLS-II LH Parameters Assumptions Summary Harms, LCLS-II Accelerator Physics 9 Apr 2014

3. The Linearizer module - What is it, What does it do? 3 3Harms, LCLS-II Accelerator Physics 9 Apr 2014

4. Bunch Compression with 3.9 GHz Module 4 After acceleration w/oAfter compression w/o With 3rd harmonic From P Piot Short bunch Flat bunch ~250 fs  From M Dohlus et al 4Harms, LCLS-II Accelerator Physics 9 Apr 2014

5. Test Results 5 Entire cryomodule was first tested at DESY in their CryoModule Test Bench (CMTB) prior to installation in FLASH –Successful assembly –Successful transatlantic shipment –Some rework at DESY Longitudinal realignment Instrumentation terminations Harms, LCLS-II Accelerator Physics 9 Apr 20145

6. ACC39 Performance 6 Set up for lasing has gone from expert tune up (shifts) to nearly immediate after turn-on 6Harms, LCLS-II Accelerator Physics 9 Apr 2014

7. ACC39 Performance 7 ACC39 routinely operates at 18.9 to 19.7 MV/m Capable of operation at 22 MV/m –Limitation set by thermal interlocks – concern about compromising HOM’s on Cavities 3 & 5 (trimmed 2-post style) Amplitude stability ≤ 2x10 -5 pulse-to-pulse Phase stability ≤ 0.003° pulse-to-pulse 7Harms, LCLS-II Accelerator Physics 9 Apr 2014

8. Experiences & Lessons Learned (and applied) New infrastructure had to be built –Commissioning in parallel with qualifying components Vertical test stand Horizontal Test Stand Coupler Conditioning Clean rooms … HOM redesign –Not simply a scaled version –Modeling and prototyping important –Robust design is the end result HOM coupler antennae –Prototyping and testing is vital before placing order Engineering Notes & Operational Readiness Clearance Transatlantic Transport of a complete cryomodule Welding certification –Especially Helium vessels ‘New’ technologies explored and applied 8Harms, LCLS-II Accelerator Physics 9 Apr 2014

9. Looking Ahead – CW Operation Heat Load/Cryogenic piping –Limit total cryomodule heat load to <250 watts –Dynamic Heat Load needs to be revisited Estimated heat load ~15 watts/cavity @ 15 MV/m Input coupler power capability/cooling –Current design should be good to ~2kW cw, but needs to be re-analyzed Studies are possible using coupler stand at A0 with a cw amplifier –Is a variable coupler necessary rather than current ‘fixed’ design 9Harms, LCLS-II Accelerator Physics 9 Apr 2014

10. Looking Ahead – CW Operation (2) HOM coupler and feedthrough capability –Current (single-post) ‘Formteil’ design multi-pacting lower bound ~25 MV/m –Feedthrough – adequate cooling? –Simulation needed to look at modes (THz?) present in the ends Absorbing material needed in beam pipe? Preliminary simulations begun Microphonics/Fast tuning –Current tuner is slow (blade) tuner only –Cavities are already fairly stiff – resistant to microphonics/LFD –Consider addition of fast/piezo’s or passive microphonics compensation 10Harms, LCLS-II Accelerator Physics 9 Apr 2014

11. Looking Ahead – CW Operation (3) Cavity Global thermal limit is estimated to be of order 25 MV/m Alignment –Offset = HOM power considerations –Tilt = transverse emittance implications Other issues to consider –Beam diagnostics, especially internal to module –Quads, dipoles –Cryogenic and vacuum interconnectability to adjacent components –Standalone vs. Integrated module 11Harms, LCLS-II Accelerator Physics 9 Apr 2014

12. 12 E. HarmsAPT Seminar 14 January 2014 LCLS-II Layout P. Emma, L. Wang, C. Papadopoulos M. Ross Harms, LCLS-II Accelerator Physics 9 Apr 2014

13. 13 E. HarmsAPT Seminar 14 January 2014 Proposed Parameter Set Harms, LCLS-II Accelerator Physics 9 Apr 2014

14. Cryomodule –8 cavities per Cryomodule with 2 Cryomodules –Total heat load ~200 W / cryomodule –No magnet, corrector, or BPM’s in 3.9GHz CM’s –Magnets/Quad/BPM will be downstream in warm section –Cavities spaced for Q0 > 2e9 –Beam pipe tapering from 1.3 GHz CM to 3.9 GHz CM –Length of interconnection (distance between CM’s) is free no requirements in term of wavelength. –Larger diameter 2-phase pipe/nozzle akin to 1.3 GHz will provide additional cooling than existing design –Cryo interface will be CM2/3 upstream and 'standard' feedbox immediately downstream –Design of cryomodule will strive to bring all signal cables out on the aisle side –Cryomodule will be cooled with the proposed 2nd cryoplant capable of ~1kW at 2K along with the other upstream (non-main Linac) CM’s –Cavity-to cavity distance is short (as in FLASH) –HOM (beam pipe) absorber likely placed between two 3.9 GHz CM’s 14 E. HarmsAPT Seminar 14 January 2014 3.9 GHz Section Assumptions - 1 Harms, LCLS-II Accelerator Physics 9 Apr 2014

15. Cavities –Capable of 14.5 MV/m cw –Power dissipation ~17 W / cavity, maximum HOM power ~13 W / CM or 1.6 W / cavity (>50% will dissipated at 70K or RT) –Blade tuner design with 3 piezos incorporated. –HOM coupler signals may be used for beam offset measurements –Consider modest Q0 improvement development program (N2 doping), but low priority and is not project critical 1- and 9-cell cavities are available for processing & testing 15 E. HarmsAPT Seminar 14 January 2014 3.9 GHz Section Assumptions - 2 Harms, LCLS-II Accelerator Physics 9 Apr 2014

16. Couplers –Cavity orientation for placement downstream and every second rotated by 180° –Dig tunnel wall if necessary to make room for coupler clearance “not out of the question” –Waveguide from back side of CM will be pre-assembled and extend to top of CM for connection –Two options for klystron to CM feed: Waveguide or coax WG option is preferable coax is lossier, possible center conductor heating –Coupler will require modifications for CW regime –Fixed coupling (Q~1.e7) looks OK. 16 E. HarmsAPT Seminar 14 January 2014 3.9 GHz Section Assumptions - 3 Harms, LCLS-II Accelerator Physics 9 Apr 2014

17. 17 E. HarmsAPT Seminar 14 January 2014 Coupler Orientation Options Start here Goal 1.30 GHz Fermilab Cryomodule Layout: FLASH Cryomodule Layout: XFEL Cryomodule Layout: Arun Saini, N. Solyak Harms, LCLS-II Accelerator Physics 9 Apr 2014

18. 18 E. HarmsAPT Seminar 14 January 2014 Coupler Orientation Summary Start here Goal 1.30 GHz Beam optics through harmonic section is studied. Fermilab configuration XFEL Configuration ILC type cryomodule Coupler RF kick results in significant emittance growth. Local compensation of coupler kick is possible and emittance dilution can be minimized using different orientations of alternative cavity. XFEL configuration provides best solution in terms of emittance compensation. Arun Saini, N. Solyak Harms, LCLS-II Accelerator Physics 9 Apr 2014

19. Testing –Test cavities in VTS and HTS (subset) maybe ANL/Ostroumov team will do horizontal testing –Cryomodules will be cooled down and tested prior to transport to SLAC –3 kW cw 3.9 GHz in hand – needs to be made operational –3.9 GHz Infrastructure exists (or can be modified) to do most testing cavities couplers cryomodules 19 E. HarmsAPT Seminar 14 January 2014 3.9 GHz Section Assumptions - 4 Harms, LCLS-II Accelerator Physics 9 Apr 2014

20. Actions –Will try to start from XFEL CM design --> (Elvin and Tom) –May want to run cavities in pairs to compensate coupler kicks - not clear that this is necessary (Arun to evaluate) –Andrei is evaluating wakefields but expect them to be small –Need to specify alignment tolerances (Arun to evaluate) –Need to test new 3.9 GHz FPC in CW operation --> (need schedule) –In addition to testing FPC new design, task force needs to be formed to look at and review design Key Dates –1 June 2014: FRS submitted –6 October 2014: Design Review 20 E. HarmsAPT Seminar 14 January 2014 3.9 GHz Section Actions & Dates Harms, LCLS-II Accelerator Physics 9 Apr 2014

21. 3.9 GHz (pulsed) operating at FLASH XFEL building a similar module Technology can be applied for LCLS-II Issues related to cw operation identified - manageable Parameter list compiled – needs to be verified List of assumptions and actions for LCLS-II LH compiled Simulation/modeling work begun –Coupler design and orientation Effort needs further formalization Do as much work as possible now Summary 21Harms, LCLS-II Accelerator Physics 9 Apr 2014

22. Thanks 22Harms, LCLS-II Accelerator Physics 9 Apr 2014