Transcript LHC Luminosity Upgrade using Crab Cavities

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)
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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LHC crab cavities
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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,
possibly Nb3Sn triplet & b*~0.15 m
+ injector
upgrade
complementary measures 2010-2017:
e.g. long-range beam-beam compensation,
crab cavities, new/upgraded injectors, advanced
collimators, coherent e- cooling, e- lenses
phase-2 might be just phase-1 plus complementary measures
longer term (2020?): energy upgrade, LHeC,…
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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)
D0 dipole
•
•
J.-P. Koutchouk
stronger 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
large Piwinski
angle (LPA)
F. Ruggiero,
W. Scandale.
F. Zimmermann
full crab crossing (FCC)
stronger triplet
magnets
L. Evans,
W. Scandale,
F. Zimmermann
• 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
larger-aperture triplet magnets
•
•
•
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
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LHC parameters
parameter
symbol
transverse emittance
e [mm]
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
Dt [ns]
25
25
25
25
50
beam current
I [A]
0.58
0.86
0.86
0.86
1.22
Gauss
Gauss
Gauss
Gauss
Flat
longitudinal profile
nominal
ultimate
Early Sep.
Full Crab Xing
L. Piw Angle
rms bunch length
sz [cm]
7.55
7.55
7.55
7.55
11.8
beta* at IP1&5
b* [m]
0.55
0.5
0.08
0.08
0.25
full crossing angle
qc [mrad]
285
315
0
0
381
Piwinski parameter
f=qcsz/(2*sx*)
0.64
0.75
0
0
2.0
1
1
0.86
0.86
0.99
1
2.3
15.5
15.5
10.7
4.5
4.3
3.7
3.7
5.3
D0 + crab
crab
wire comp.
hourglass reduction
peak luminosity
L [1034 cm-2s-1]
extent luminous region
sl [cm]
comment
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nominal
ultimate
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for operation at beam-beam limit
with alternating planes of crossing at two IPs
↑ LPA
↑ ES/FCC
f rev
1
L=
nb * Nb DQbb FprofileFhg
2rp
b
↓ LPA
↑↑ LPA
↓↓ ES/FCC
↓ LPA
↑ LPA
↓ ES/FCC
where (DQbb) = total beam-beam tune shift;
peak luminosity with respect to ultimate LHC (2.4 x nominal):
ES or FCC:
LPA:
x6
½
x 1.3
x2 x2.9x1.3
x 0.86 = 6.7
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 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
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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 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
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Small crossing angle (0.3~0.6 mrad)
IP4
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IP 6 or 7(8)
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IP4 and arc tunability (Global CCs)
Switching polarities may increase beta up to 800m,
idea by K. Oide
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]
Wide range tunability in arc, to get good phase advance between CC and IP.
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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 beamloading 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
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Local scheme: space challenge
D2
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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.
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Noise tolerances
White noise, very pessimistic, below 10^-3 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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Ralph Assmann
•
•
•
•
•
•
Collimation
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
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Global CC’s impact on collimation
•
Set-up errors of collimators and transient
changes of beam:
~ 0.3 s
– Estimate:
•
(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
Nominal LHC
- 0.5 sx
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)
Ralph Assmann
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LHC-CC08
joint BNL/CARE-HHH/US-LARP
BNL, 25-26 Feb. 2008
B. Palmer
RF Deflector
( Crab Cavity )
HER
LER
Electrons
Positrons
1.44 MV
Crossing Angle
(11 x 2 m rad.)
1.41 MV
workshop,
Head-on
Collision
1.44 MV
1.41 MV
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
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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 0.5σ
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
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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
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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
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BNL-AES prototype crab cavity
M. Cole
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Preliminary cavity design
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Conclusions
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!
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