LHC Luminosity Upgrade using Crab CavitiesLHC 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-2003-506395)

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CollaboratorsCollaborators

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• 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 Nb3Sn triplet & *~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,…

phase-2 might be just phase-1 plus complementary measures

+ injector upgrade

3

Geometric luminosity gainGeometric luminosity gain

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Good agreements between GUINEA-PIG simulations and formulae

Crab Cavities will enhance luminosity for all upgrade phases (including nominal LHC)

-

LHC upgrade pathsLHC upgrade paths

• ultimate beam (1.7x10ultimate beam (1.7x101111 protons/bunch, 25 spacing), protons/bunch, 25 spacing), * ~10 cm * ~10 cm

• early-separation dipoles in side detectors , crab cavities early-separation dipoles in side detectors , crab cavities

→ → hardware inside ATLAS & CMS detectors, hardware inside ATLAS & CMS detectors,

first hadron crab cavities; off-first hadron crab cavities; off-

stronger triplet magnets

D0 dipole

small-angle

crab cavity

J.-P. Koutchoukearly separation (ES)early separation (ES)

stronger triplet magnets

small-angle

crab cavity

• ultimate LHC beam (1.7x10ultimate LHC beam (1.7x101111 protons/bunch, 25 spacing) protons/bunch, 25 spacing) * ~10 cm * ~10 cm

• crab cavities with 60% higher voltage crab cavities with 60% higher voltage

→ → first hadron crab cavities, off-first hadron crab cavities, off--beat-beat

L. Evans,W. Scandale,F. Zimmermann

full crab crossing (FCC)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(5x101111 protons/bunch) 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 novel operating regime for hadron colliders, colliders,

beam generationbeam generation

F. Ruggiero,W. Scandale.F. Zimmermann

large Piwinski large Piwinski angle (LPA)angle (LPA)

5

LHC parametersLHC parameters

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parameter symbol nominal ultimate Early Sep. Full Crab Xing L. Piw Angle

transverse emittance [m] 3.75 3.75 3.75 3.75 3.75

protons per bunch Nb [1011] 1.15 1.7 1.7 1.7 4.9

bunch spacing t [ns] 25 25 25 25 50

beam current I [A] 0.58 0.86 0.86 0.86 1.22

longitudinal profile Gauss Gauss Gauss Gauss Flat

rms bunch length z [cm] 7.55 7.55 7.55 7.55 11.8

beta* at IP1&5 [m] 0.55 0.5 0.08 0.08 0.25

full crossing angle c [rad] 285 315 0 0 381

Piwinski parametercz/(2*x*) 0.64 0.75 0 0 2.0

hourglass reduction 1 1 0.86 0.86 0.99

peak luminosity L [1034 cm-2s-1] 1 2.3 15.5 15.5 10.7

extent luminous region l [cm] 4.5 4.3 3.7 3.7 5.3

comment nominal ultimate D0 + crab crab wire comp.

for operation at beam-beam limitwith alternating planes of crossing at two IPs

hgprofilebbbbp

rev FFQNnr

fL

*

1

2

↓↓ ES/FCC↑↑ LPA

↓ LPA

↓ LPA

where (Qbb) = 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 luminosity23/04/2008, Shanghai 7LHC crab cavities

Crab crossingCrab crossing

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Palmer: linear collider [1]

Oide and Yokoya: CC in storage rings

(1989)

KEKB: Global CC in rings

Possible LHC crab options: phase 0Possible LHC crab options: phase 0

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• 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 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

Possible LHC crab options: phase 1Possible LHC crab options: phase 1

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• 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)Small crossing angle (0.3~0.6 mrad)

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IP4IP 6 or 7(8)

IP4 and arc tunability (Global CCs)IP4 and arc tunability (Global CCs)

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Possibility of even higher beta functions with switching polarities (MQYs) or new hardware.

One arc has 23 cells→ ΔØx = [-0.60,0.11] and ΔØy = [-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 statusLHC Main RF status

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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, 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

Local scheme: space challengeLocal scheme: space challenge

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D2

New approach: separation between D1-D2, after phase 1New approach: separation between D1-D2, after phase 1

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•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 tolerancesNoise tolerances

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White noise, very pessimistic, below 10^-3 deg tolerance, at the edge of technology?!

Modulated jitterModulated jitter

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assuming noise spectra measured at KEKB crab cavities, LHC transverse emittance growth is negligble

Synchro-betatron resonances with Global CCsSynchro-betatron resonances with Global CCs

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CCs enhance the 3rd, 5th, 6th, 7th Qs sidebandsDangerous 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

101055 Turns DA with CCs Turns DA with CCs

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initial momentum offset = 2.5 sigma (standard LHC value), beam energy 7TeV

CollimationCollimation

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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 collimationGlobal CC’s impact on collimation

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Ralph Assmann

- 0.5 x

• Set-up errors of collimators and transient changes of beam:

– Estimate: ~ 0.3 (60 m)• Off-momentum beta beat mixes up the 6D mixes up the 6D

phase spacephase space and can corrupt collimation corrupt collimation performanceperformance (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-CC08LHC-CC08joint BNL/CARE-HHH/US-LARP workshop, BNL, 25-26 Feb. 2008use 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

RF Deflector( Crab Cavity )

Head-onCollision

Crossing Angle (11 x 2 m rad.)

Electrons PositronsLERHER

1.41 MV

1.41 MV

1.44 MV

1.44 MV

K. Oide

B. Palmer

22

BNL LHC-CC workshop Charge and conclusionsBNL LHC-CC workshop Charge and conclusions

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• 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 ICollimation has to evaluate the exact loss maps and additional heat deposition from oscillating bunch. Configuration to allow for the extra 0.5σ orbitCan 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)BNL LHC-CC workshop Charge and conclusions (con’t 2)

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• 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

BNL LHC-CC workshop Charge and conclusions (con’t 3)BNL LHC-CC workshop Charge and conclusions (con’t 3)

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• 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 resultshttps://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

BNL-AES prototype crab cavityBNL-AES prototype crab cavity

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M. Cole

Preliminary cavity designPreliminary cavity design

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ConclusionsConclusions

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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 2011-2012

5. 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!