LHC Luminosity Upgrade using Crab Cavities

1. LHC Luminosity Upgrade using Crab Cavities Rama Calaga, Yi-Peng Sun, Rogelio Tomas, Frank Zimmermann AB/ABP Group, CERN and BNL/US-LARP Presented at Shanghai deflecting cavity workshop, 23~25th April 2008 Acknowledge: R. Assmann, J. Tuckmantel, S. Fartoukh, D. Schulte, R. de Maria, C. Bracco, T. Weiler, H. Padamsee, K. Oide, I. Ben-Zvi, and LHC-CC collaborators Supported by the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT-2003-506395)

2. Collaborators • AES M. Cole • Brookhaven National Lab I. Ben-Zvi, R. Calaga, S. Peggs •CERN F. Caspers, U. Dorda, Y. Sun, R. Tomas, J. Tuckmantel, F. Zimmermann • Daresbury Lab & Cockcroft Institute C. Beard, G. Burt, P. McIntosh, A. Kalinin, A. Dexter, P. Goudket, L. Ma • FNAL L. Bellantoni, P. Limon, N. Solyak, G. Wu, S. Yakovlev • Jefferson Lab H. Wang, R. Rimmer •KEK K. Akai, K. Oide, K. Ohmi, Y. Morita, K. Yamamoto •LBNL J. Byrd, D. Li • SLAC C. Adolphsen, V. Dolgashev, Z. Li, T. Markiewicz, C. Ng, A. Seryi, J. Smith, S. Tantawi, L. Xiao • ANL, INFN, Tech-X, ... LHC crab cavities

3. staged approach to LHC upgrade “phase-1” 2013: new triplets, D1, TAS, b*=0.25 m in IP1 & 5, reliable LHC operation at ~2x luminosity; beam from new Linac4 “phase-2” 2017: target luminosity 10x nominal, possiblyNb3Sn triplet & b*~0.15 m complementary measures 2010-2017: e.g. long-range beam-beam compensation, crab cavities, new/upgraded injectors, advanced collimators, coherent e- cooling, e- lenses longer term (2020?): energy upgrade, LHeC,… + injector upgrade phase-2 might be just phase-1 plus complementary measures

4. Geometric luminosity gain Crab Cavities will enhance luminosity for all upgrade phases (including nominal LHC) - Good agreements between GUINEA-PIG simulations and formulae LHC crab cavities

5. LHC upgrade paths stronger triplet magnets stronger triplet magnets D0 dipole small-angle crab cavity small-angle crab cavity early separation (ES) full crab crossing (FCC) L. Evans, W. Scandale, F. Zimmermann J.-P. Koutchouk larger-aperture triplet magnets • ultimate beam (1.7x1011 protons/bunch, 25 spacing), b* ~10 cm • early-separation dipoles in side detectors , crab cavities • → hardware inside ATLAS & CMS detectors, • first hadron crab cavities; off-d b • ultimate LHC beam (1.7x1011 protons/bunch, 25 spacing) • b* ~10 cm • crab cavities with 60% higher voltage • → first hadron crab cavities, off-d b-beat wire compensator large Piwinski angle (LPA) • 50 ns spacing, longer & more intense bunches • (5x1011 protons/bunch) • b*~25 cm, no elements inside detectors • long-range beam-beam wire compensation • → novel operating regime for hadron colliders, • beam generation F. Ruggiero, W. Scandale. F. Zimmermann

6. LHC parameters LHC crab cavities

7. for operation at beam-beam limit with alternating planes of crossing at two IPs ↑ LPA ↑ ES/FCC ↑↑ LPA ↑ LPA ↓ ES/FCC ↓ LPA ↓↓ ES/FCC ↓ LPA where (DQbb) = total beam-beam tune shift; peak luminosity with respect to ultimate LHC (2.4 x nominal): ES or FCC: x 6 x 1.3 x 0.86 = 6.7 LPA: ½ x2 x2.9x1.3 x1.4 = 5.3 what matters is the integrated luminosity LHC crab cavities

8. Crab crossing Palmer: linear collider [1] Oide and Yokoya: CC in storage rings (1989) KEKB: Global CC in rings LHC crab cavities

9. Possible LHC crab options: phase 0 • One prototype crab cavity in one ring for global crabbing • – Emphasizes the development and testing of the cavity and cryomodule in LHC environment. • – Luminosity gain (5-7%) with β*=0.55 m. • – Limited information about beam-beam interactions. • – Emittance growth due to effect of crab RF noise together with beam-beam tune spread; Effect of global crab cavities on collimation cleaning efficiency; Effect of crab  cavity impedance. • • Two prototypecrab cavities in the global crabbing mode, one per beam • – Information on the beam-beam interactions in head-on collisions. • – Possibly 10 -15% gain in luminosity (β*=0.55 m), in ONE IP. • – The increased luminosity would make it more attractive for LHC to support the installation. • – The small increase in luminosity however may be difficult to confirm. Courtesy BNL workshop summaries LHC crab cavities

10. Possible LHC crab options: phase 1 • Four crab cavities in the global mode to benefit two interaction regions • – Luminosity gain greater at lower β*, e.g. ~50% at β*=0.25m. • – More expensive than phase 0 and would need more time to implement. • – The potential benefit to two interaction regions would probably generate more support for installation. • • Four crab cavities in the local crabbing mode • – Luminosity gain greater at lower β*, e.g. ~50% at β*=0.25m. • – More expensive, as above. • – Have to address the tighter space availability near the IPs. • –Squashed cell geometry needed for polarization of the crab mode. • – Accommodate the crab cavity with vertical crossing angles. Courtesy BNL workshop summaries LHC crab cavities

11. Small crossing angle (0.3~0.6 mrad) IP 6 or 7(8) IP4 LHC crab cavities

12. IP4 and arc tunability (Global CCs) Switching polarities may increase beta up to 800m, idea by K. Oide One arc has 23 cells→ ΔØx = [-0.60,0.11] and ΔØy = [-0.16,0.46] Possibility of even higher beta functions with switching polarities (MQYs) or new hardware. Wide range tunability in arc, to get good phase advance between CC and IP. LHC crab cavities

13. P. Baudrenghien & T. Linnecar LHC Main RF status • Two independent rings • 4 cryostats (2/beam) plus 1 reserve, each module 4 SC cavities • Super Conducting SW 400 MHz cavities, VRF = 2 MV (nominal max.) • Tuner: mechanical (range > 200 kHz), large tuning range (180 kHz @ 9kHz/s) for beam-loading compensation • Movable Main Coupler, 300 kW full reflection, (12000 < QL < 180000) • 1 MV /cavity at injection with QL = 20000 • 2 MV/cavity during physics with QL = 60000 LHC crab cavities

14. Local scheme: space challenge D2 LHC crab cavities

15. New approach: separation between D1-D2, after phase 1 Local CC D11&D12 • Approximate 10 sigma beam envelope. • New idea from S. Fartoukh: Move D2, Q4 and Q5 towards the arcs to improve matchability and LSS aperture (space between D1 and D2 is increased). • Separation of beams to 27cm for 20m longitudinally achievable with present technology. LHC crab cavities

16. Noise tolerances White noise, very pessimistic, below 10^-2 deg tolerance, at the edge of technology?! LHC crab cavities

17. Modulated jitter assuming noise spectra measured at KEKB crab cavities, LHC transverse emittance growth is negligble LHC crab cavities

18. Synchro-betatron resonances with Global CCs ongoing study CCs enhance the 3rd, 5th, 6th, 7th Qs sidebands Dangerous synchrobetatron resonances could be: Qx - Qy + 6Qs, Qx + 2Qy + 30Qs, ... CCs will suppress Synchro-betatron resonances induced by the crossing angle (not included in the FFT shown). LHC crab cavities

19. 105 Turns DA with CCs initial momentum offset = 2.5 sigma (standard LHC value), beam energy 7TeV LHC crab cavities

20. Collimation Ralph Assmann • The LHC collimators must sit very tight on the beam to provide good passive protection and cleaning. • As a consequence, the 6D phase space must be well defined. Tolerances on relative settings (retraction) are critical. • Off-momentum beta beat is important and is being addressed (S. Fartoukh). Larger off-momentum beta beat with upgrade optics. • A global crab cavity scheme will further complicate the situation. • Tests with a global crab scheme can be performed with a few nominal bunches (increase of specific luminosity). • Further work is ongoing and required. Interference local crab cavities and collimation in experimental insertions. Off-momentum beta-beat a big problem, global CC only add a small fraction 23/04/2008, Shanghai LHC crab cavities 20

21. Global CC’s impact on collimation • Set-up errors of collimators and transient changes of beam: • Estimate: ~ 0.3 s (60 mm) • Off-momentum beta beat mixes up the 6D phase space and can corrupt collimation performance(e.g. loss of horizontal retraction for tertiary tungsten collimators): • Estimate for tertiary collimators (margin 0.8 s): ~ 0.5 s • Estimate for absorbers (margin 2.5 s): ~ 1.5 s • Global crab cavity further reduces horizontal retraction: • Estimate: ongoing, in the order of 0.5 s • Off-momentum beta beating must be fixed before installing global crab cavities (solution with complete correction in progress for nominal LHC and upgrade phase 1, by S. Fartoukh) Nominal LHC - 0.5 sx Ralph Assmann LHC crab cavities

22. LHC-CC08 joint BNL/CARE-HHH/US-LARP workshop, BNL, 25-26 Feb. 2008 use KEKB experience plan R&D for crab cavities phased approach: (1) prototype construction [SBIR] (2) “global” crab cavity test in IR4, (3) “local” crab cavities in IR1 & 5 international collaboration K. Oide B. Palmer R. Calaga

23. BNL LHC-CC workshop Charge and conclusions • Choice of Freq • 800 MHz may be best for Phase 0, lower frequencies if compact cavities are available (space challenges and more crab voltage). BB simulations with RF curvature NEEDED • How much free space • 10m for Phase 0 (IP4) & 20m for Phase I (IP5/1 with new optics) • Global or Local Phase I • Collimation has to evaluate the exact loss maps and additional heat deposition from oscillating bunch. Configuration to allow for the extra 0.5σ orbit • Can we optimize the existing collimators to exploit oscillating bunch (longitudinal collimation) and reduce impedance • Noise Effects • Need more S-S simulations to understand any issues but current estimates and RF jitter suggests that LLRF can keep the jitter within required tolerances LHC crab cavities

24. BNL LHC-CC workshop Charge and conclusions (con’t 2) • R&D Objectives – Adapt from previous R&D: LLRF, Couplers (LOM), Cryostat(LHC), Tuners – Focus priorities: Collimation, Impedance, Final cavity design and couplers, Common cryostat, Simulations & Measurement on models • Cavity Impedance needs careful evaluation to establish single bunch & coupled bunch effects. Start with assumptions used for existing narrow band impedances in the LHC RF Control – Qext 105 − 106 ? Power Amplifiers: IOT (50-100 kW) ? – Power handling - beam pipe coax + ferrites robust for high currents – Phase jitter control easily possible ≤ 1 × 10−2 deg, need ≤ 1 × 10−3 degree slightly challenging (800 MHz) BNL LHC-CC workshop: http://indico.cern.ch/conferenceDisplay.py?confId=24200 23/04/2008, Shanghai LHC crab cavities 24

25. BNL LHC-CC workshop Charge and conclusions (con’t 3) • Design, Fabrication & Processing • – Gradient of 2.5-3 MV for 2 cell 800 MHz cavity (Epeak = 40 MV/m, Bpeak = 120mT) • – 1-2 crab structures/beam should be sufficient. Additional degrees of freedom from optics • – 0.75 squash ratio is reasonable to fabricate and will fit in new optics with VV crossing (exotic structures in parallel) • – Cavity aperture > 10 cm diameter (smallest aperture 8 cm) (HOM extracting) • – Various designs of couplers available, beam pipe coax + waveguide may be most effective and robust • Use TWiki as the central repository for design & simulation results https://twiki.cern.ch/twiki/bin/view/Main/LHCCrabCavities • Identify various people involved in different studies and consolidate • What are current resources available & what is needed LHC crab cavities

26. BNL-AES prototype crab cavity M. Cole LHC crab cavities

27. Cavity design 23/04/2008, Shanghai LHC crab cavities 27

28. Conclusions • Phased crab cavity program in place for LHC • Crab cavities decoupled from the rest of LHC upgrade; they would boost luminosity for all LHC stages • Global collaboration, and synergy with ILC, CLIC and light sources • First prototype beam testing approximately in 2011-2012 • KEKB experience is critical • New coupler designs for robust damping needed • Collimation, impedance and noise issues require new simulations, tests, and developments • LHC constraints could benefit from novel compact cavity Your collaboration is welcome! LHC crab cavities