LHC Luminosity Upgrade using Crab Cavities

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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,
2325th 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)
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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, ...
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staged approach to LHC upgrade phase-1
2013 new triplets, D1, TAS, b0.25 m in IP1
5, reliable LHC operation at 2x
luminosity beam from new Linac4 phase-2
2017 target luminosity 10x nominal,
possiblyNb3Sn triplet b0.15 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
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Geometric luminosity gain
Crab Cavities will enhance luminosity for all
upgrade phases (including nominal LHC)
-
Good agreements between GUINEA-PIG simulations
and formulae
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LHC upgrade paths
early separation (ES)
full crab crossing (FCC)
L. Evans, W. Scandale, F. Zimmermann
J.-P. Koutchouk

• 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

large Piwinski angle (LPA)

• 50 ns spacing, longer more intense bunches
• (5x1011 protons/bunch)
• b25 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
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LHC parameters
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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
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Crab crossing
Palmer linear collider 1
Oide and Yokoya CC in storage rings (1989)
KEKB Global CC in rings
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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 ß0.55 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 (ß 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
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Possible LHC crab options phase 1

• Four crab cavities in the global mode to benefit
  two interaction regions
• Luminosity gain greater at lower ß, e.g. 50
  at ß0.25m.
• 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 ß, e.g. 50
  at ß0.25m.
• 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
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Small crossing angle (0.30.6 mrad)
IP 6 or 7(8)
IP4
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IP4 and arc tunability (Global CCs)
Switching polarities may increase beta up to
800m, idea by K. Oide
One arc has 23 cells? ?Øx -0.60,0.11 and ?Øy
-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.
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LHC Main RF status
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 gt 200 kHz ), large
  tuning range (180 kHz _at_ 9kHz/s) for beam-loading
  compensation
• Movable Main Coupler, 300 kW full reflection,
  (12000 lt QL lt 180000)
• 1 MV /cavity at injection with QL 20000
• 2 MV/cavity during physics with QL 60000

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Local scheme space challenge
D2
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New approach separation between D1-D2, after
phase 1
Local CC
D11D12

• 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.

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Noise tolerances
White noise, very pessimistic, below 10-2 deg
tolerance, at the edge of technology?!
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Modulated jitter
assuming noise spectra measured at KEKB crab
cavities, LHC transverse emittance growth is
negligble
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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).
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105 Turns DA with CCs
initial momentum offset 2.5 sigma (standard LHC
value), beam energy 7TeV
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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
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Global CCs 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
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LHC-CC08
joint BNL/CARE-HHH/US-LARP workshop, BNL,
25-26 Feb. 2008
use KEKB experience plan RD 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
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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 0.5s
  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

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BNL LHC-CC workshop Charge and conclusions (cont
2)

• RD Objectives
• Adapt from previous RD 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/confere
nceDisplay.py?confId24200
23/04/2008, Shanghai
LHC crab cavities
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BNL LHC-CC workshop Charge and conclusions (cont
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 gt 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
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BNL-AES prototype crab cavity
M. Cole
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Cavity design
23/04/2008, Shanghai
LHC crab cavities
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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!