LHC Luminosity Upgrade using Crab Cavities Rama Calaga, Yi-Peng Sun, Rogelio Tomas, Frank Zimmermann 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 Presented at Shanghai deflecting cavity workshop, 23~25th April 2008 AB/ABP Group, CERN and BNL/US-LARP Supported by the European Community-Research Infrastructure Activity under the FP6 “Structuring the European Research Area” programme (CARE, contract number RII3-CT )

Collaborators 23/04/2008, ShanghaiLHC crab cavities2 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,...

staged approach to LHC upgrade “phase-1” 2013: new triplets, D1, TAS,  *=0.25 m in IP1 & 5, reliable LHC operation at ~2x luminosity; beam from new Linac4 “phase-2” 2017: target luminosity 10x nominal, possibly Nb 3 Sn triplet &  *~0.15 m complementary measures : 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,… phase-2 might be just phase-1 plus complementary measures + injector upgrade 3

Geometric luminosity gain 23/04/2008, ShanghaiLHC crab cavities4 Good agreements between GUINEA-PIG simulations and formulae Crab Cavities will enhance luminosity for all upgrade phases (including nominal LHC) -

LHC upgrade paths ultimate beam (1.7x10 11 protons/bunch, 25 spacing),  * ~10 cm ultimate beam (1.7x10 11 protons/bunch, 25 spacing),  * ~10 cm early-separation dipoles in side detectors, crab cavities early-separation dipoles in side detectors, crab cavities → hardware inside ATLAS & CMS detectors, first hadron crab cavities; off-  stronger triplet magnets D0 dipole small-angle crab cavity J.-P. Koutchouk early separation (ES) stronger triplet magnets small-angle crab cavity ultimate LHC beam (1.7x10 11 protons/bunch, 25 spacing) ultimate LHC beam (1.7x10 11 protons/bunch, 25 spacing)   * ~10 cm crab cavities with 60% higher voltage crab cavities with 60% higher voltage → first hadron crab cavities, off-  -beat L. Evans, W. Scandale, F. Zimmermann full crab crossing (FCC) wire compensator larger-aperture triplet magnets 50 ns spacing, longer & more intense bunches 50 ns spacing, longer & more intense bunches (5x10 11 protons/bunch)  *~25 cm, no elements inside detectors  *~25 cm, no elements inside detectors long-range beam-beam wire compensation long-range beam-beam wire compensation → novel operating regime for hadron colliders, beam generation F. Ruggiero, W. Scandale. F. Zimmermann large Piwinski angle (LPA) 5

LHC parameters 23/04/2008, ShanghaiLHC crab cavities6 parametersymbolnominalultimateEarly Sep.Full Crab XingL. Piw Angle transverse emittance  [  m] 3.75 protons per bunchN b [10 11 ] bunch spacing  t [ns] beam currentI [A] longitudinal profile Gauss Flat rms bunch length  z [cm] beta* at IP1&5  [m] full crossing angle  c [  rad] Piwinski parameter  c  z /(2*  x *) hourglass reduction peak luminosityL [10 34 cm -2 s -1 ] extent luminous region  l [cm] comment nominalultimateD0 + crab crabwire comp.

for operation at beam-beam limit with alternating planes of crossing at two IPs ↓↓ ES/FCC ↑↑ LPA ↓ LPA where (  Q bb ) = total beam-beam tune shift; ↑ LPA↓ ES/FCC peak luminosity with respect to ultimate LHC (2.4 x nominal): ES or FCC: x 6 x 1.3 x 0.86 = 6.7 ↑ ES/FCC LPA: ½ x2 x2.9x1.3 x1.4 = 5.3 ↑ LPA what matters is the integrated luminosity 23/04/2008, Shanghai7LHC crab cavities

Crab crossing 23/04/2008, ShanghaiLHC crab cavities8 Palmer: linear collider [1] Oide and Yokoya: CC in storage rings (1989) KEKB: Global CC in rings

Possible LHC crab options: phase 0 23/04/2008, ShanghaiLHC crab cavities9 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 prototype crab cavities in the global crabbing mode, one per beam – Information on the beam-beam interactions in head-on collisions. – Possibly % 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

Possible LHC crab options: phase 1 23/04/2008, ShanghaiLHC crab cavities10 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

Small crossing angle (0.3~0.6 mrad) 23/04/2008, ShanghaiLHC crab cavities11 IP4 IP 6 or 7(8)

IP4 and arc tunability (Global CCs) 23/04/2008, ShanghaiLHC crab cavities12 Possibility of even higher beta functions with switching polarities (MQYs) or new hardware. One arc has 23 cells→ ΔØ x = [-0.60,0.11] and ΔØ y = [-0.16,0.46] Switching polarities may increase beta up to 800m, idea by K. Oide Wide range tunability in arc, to get good phase advance between CC and IP.

LHC Main RF status LHC Main RF status 23/04/2008, ShanghaiLHC crab cavities13 P. Baudrenghien & T. Linnecar – Two independent rings – 4 cryostats (2/beam) plus 1 reserve, each module 4 SC cavities – Super Conducting SW 400 MHz cavities, V RF = 2 MV (nominal max.) – Tuner: mechanical (range > 200 kHz ), large tuning range (180 9kHz/s) for beam- loading compensation – Movable Main Coupler, 300 kW full reflection, (12000 < Q L < ) 1 MV /cavity at injection with Q L = MV/cavity during physics with Q L = 60000

Local scheme: space challenge 23/04/2008, ShanghaiLHC crab cavities14 D2

New approach: separation between D1-D2, after phase 1 23/04/2008, ShanghaiLHC crab cavities15 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. D11&D12 Local CC

Noise tolerances 23/04/2008, ShanghaiLHC crab cavities16 White noise, very pessimistic, below 10^-3 deg tolerance, at the edge of technology?!

Modulated jitter 23/04/2008, ShanghaiLHC crab cavities17 assuming noise spectra measured at KEKB crab cavities, LHC transverse emittance growth is negligble

Synchro-betatron resonances with Global CCs 23/04/2008, ShanghaiLHC crab cavities18 CCs enhance the 3 rd, 5 th, 6 th, 7 th 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). ongoing study

10 5 Turns DA with CCs 23/04/2008, ShanghaiLHC crab cavities19 initial momentum offset = 2.5 sigma (standard LHC value), beam energy 7TeV

Collimation 23/04/2008, ShanghaiLHC crab cavities20 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

Global CC’s impact on collimation 23/04/2008, ShanghaiLHC crab cavities21 Ralph Assmann  x Set-up errors of collimators and transient changes of beam: – Estimate: ~ 0.3  (60  m) mixes up the 6D phase spacecorrupt collimation performance 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  ): ~ 0.5  – Estimate for absorbers (margin 2.5  ): ~ 1.5  Global crab cavity further reduces horizontal retraction: – Estimate:ongoing, in the order of 0.5  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

LHC-CC08 joint BNL/CARE-HHH/US-LARP workshop, BNL, Feb 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 22

BNL LHC-CC workshop Charge and conclusions 23/04/2008, ShanghaiLHC crab cavities23 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

BNL LHC-CC workshop Charge and conclusions (con’t 2) 23/04/2008, ShanghaiLHC crab cavities24 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 – Q ext 10 5 − 10 6 ? Power Amplifiers: IOT ( 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:

BNL LHC-CC workshop Charge and conclusions (con’t 3) 23/04/2008, ShanghaiLHC crab cavities25 Design, Fabrication & Processing – Gradient of MV for 2 cell 800 MHz cavity (E peak = 40 MV/m, B peak = 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 Identify various people involved in different studies and consolidate What are current resources available & what is needed

BNL-AES prototype crab cavity 23/04/2008, ShanghaiLHC crab cavities26 M. Cole

Preliminary cavity design 23/04/2008, ShanghaiLHC crab cavities27

Conclusions 23/04/2008, ShanghaiLHC crab cavities28 1.Phased crab cavity program in place for LHC 2.Crab cavities decoupled from the rest of LHC upgrade; they would boost luminosity for all LHC stages 3.Global collaboration, and synergy with ILC, CLIC and light sources 4.First prototype beam testing approximately in KEKB experience is critical 6.New coupler designs for robust damping needed 7.Collimation, impedance and noise issues require new simulations, tests, and developments 8.LHC constraints could benefit from novel compact cavity Your collaboration is welcome!