1. “LHC-CC08” Joint BNL/US-LARP/CARE-HHH Mini-Workshop on Crab Cavities for LHC
Frank Zimmermann
Thanks to Ilan Ben-Zvi, Rama Calaga, Walter Scandale, Yi-Peng Sun, Rogelio Tomas
PAF Meeting 14 April 2008
We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 "Structuring the European Research Area" programme (CARE, contract number RII3-CT )

2. Crab Potential
analytical formula
tracking with Guinea-Pig
Y.-P. Sun

3. Reminder: LHC upgrade paths
early separation (ES)
full crab crossing (FCC)
L. Evans,
W. Scandale,
F. Zimmermann
J.-P. Koutchouk
stronger triplet
magnets
D0 dipole
small-angle
crab cavity
stronger triplet
magnets
small-angle
crab cavity
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
larger-aperture triplet magnets
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

4. full crab crossing (FCC) large Piwinski angle (LPA)
parameter
symbol
nominal
ultimate
Early Sep.
Full Crab Xing
L. Piw Angle
transverse emittance
e [mm]
3.75
protons per bunch
Nb [1011]
1.15
1.7
4.9
bunch spacing
Dt [ns] 25 50
beam current
I [A]
0.58
0.86
1.22
longitudinal profile
Gauss
Flat
rms bunch length
sz [cm]
7.55
11.8
beta* at IP1&5
b* [m]
0.55
0.5
0.08
0.25
full crossing angle
qc [mrad]
285
315
381
Piwinski parameter
f=qcsz/(2*sx*)
0.64
0.75
2.0
hourglass reduction 1
0.99
peak luminosity
L [1034 cm-2s-1]
2.3
15.5
10.7
peak events per #ing 19 44
294
403
initial lumi lifetime
tL [h] 22 14
2.2
4.5
effective luminosity
(Tturnaround=10 h)
Leff [1034 cm-2s-1]
0.46
0.91
2.4
2.5
Trun,opt [h]
21.2
17.0
6.6
9.5
(Tturnaround=5 h)
0.56
3.6
3.5
15.0
12.0
4.6
6.7
e-c heat SEY=1.4(1.3)
P [W/m]
1.07 (0.44)
1.04 (0.59)
0.36 (0.1)
SR heat load K
PSR [W/m]
0.17
0.36
image current heat
PIC [W/m]
0.15
0.33
0.78
gas-s. 100 h (10 h) tb
Pgas [W/m]
0.04 (0.38)
0.06 (0.56)
0.09 (0.9)
extent luminous region
sl [cm]
4.3
3.7
5.3
comment
D0 + crab
crab
wire comp.
full crab crossing (FCC)
large Piwinski angle (LPA)
early separation (ES)

5. 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
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,…
+ injector
upgrade
phase-2 may be phase-1 + complementary measures!

6. LHC-CC08 Statistics mini-workshop held at BNL 25-26 February
jointly organized by Ilan Ben-Zvi (Chair, BNL), Rama Calaga (LARP), Frank Z. (HHH)
~30 participants (limited by organizers)
5 CERN (R. Assmann, K.-H. Mess, R. Tomas, J. Tuck- mantel, F. Zimmermann); 4 KEK, 2 SLAC, 1 ANL, 2 LBNL, 3 FNAL, 1 AES, 4 JLAB, 6 BNL, 1 Tech-X, 3 CI (UK), 1 Cornell, 1 DESY, 1 INFN
27 presentations, >7 rounds of discussion
web site:
LHC crab TWiki:
indico.cern.ch/conferenceDisplay.py?confId=24200
twiki.cern.ch/twiki/bin/view/Main/LHCCrabCavities

7. Sessions & Speakers
introduction and overview (convener F. Zimmermann/CERN) I. Ben-Zvi. R. Palmer, R. Calaga, M. Cole
optics & LHC integration (convener K. Oide/KEK) R. Tomas, R. Assmann, Y. Morita, J. Tuckmantel
crab-cavity noise effects (convener A. Seryi/SLAC) K. Oide, K. Ohmi
design, fabrication & processing (conv. H. Padamsee/Cornell) K. Hosayama, L Turlington, P. Kneisel, H. Wang
other crab-cavity R&D in the world (convener I. Ben-Zvi/BNL) A. Seryi, P. McIntosh, A. Nassiri, F. Marcellini
impedance issues (convener R. Rimmer/JLAB) C. Montag, Z. Li, G. Burt
rf control (convener P. McIntosh/Daresbury) D. Li, A. Dexter, S. Simrock
discussion & work packages (conv. R. Calaga/LARP+BNL) F. Zimmermann, R. Calaga

8. History & Ideas
Bob Palmer – crab-cavity inventor & first workshop speaker
crab cavities – first proposed by Bob Palmer for LC, Snowmass1988
crab cavities in storage rings proposed by K. Oide and K. Yokoya, one year later in 1989 (almost 20 years passed before first
implementation in KEKB)
Bob Palmer also invented
2-in-1 magnet
revived & combined idea of “crab super disruption”

9. Key Points KEKB experience crucial
R&D plan for LHC crab cavities (R&D on couplers,
noise issues, impedance, collimation, beam- beam,…)
staged approach:
(1) prototype construction [SBIR] through 2010
(2) “global” crab cavity test in IR4 ~2011
(3) “local” crab cavities in IR1 & IR5 after LHC phase 1 upgrade
international collaboration

10. KEKB: Global CC in rings
Global Crab Scheme
K. Oide
KEKB: Global CC in rings
implemented at KEKB
could be fit into LHC IR4 (largest separation, infrastructure)
could degrade LHC cleaning efficiency, especially for b*~0.25 m

11. Yi-Peng Sun & Ralph Assmann
Collimation Issue
set-up errors of collimators and transient changes of beam:
magnitude: ~ 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):
tertiary collimators (margin 0.8 s): ~ 0.5 s
absorbers (margin 2.5 s): ~ 1.5 s
global crab cavity further reduces aperture margin:
estimate: ongoing, in the order ~ 0.5 s
Nominal LHC
- 0.5 sx
off-momentum beta beating must be fixed before installing global crab cavities! (solution in progress for nominal LHC and upgrade phase 1, by S. Fartoukh)
- 0.5 sx
Yi-Peng Sun & Ralph Assmann

12. Local Crab Scheme requires more cavities
Rama Calaga
requires more cavities
space constraints (transverse & longitudinal)
could profit from / only possible with s.c. D1
noise tolerances may be easier
should have little impact on collimation

13. LHC Crab Voltages
800
MHz
Rama Calaga

14. R&D Collaboration I. Ben-Zvi
most valuable asset : KEK experience; we should strive to add in areas unique to the LHC
borrow ILC experience for simulations, modeling, couplers etc.
various cavity shapes, couplers, tuners & cryostat designs deve- loped by various efforts around the world → cut design time
powerful simulations codes & expertise in various laboratories
R. Calaga

15. LHC-CC08 Conclusions phased crab cavity program for LHC
need for correcting off-momentum b-beating in LHC
crab cavities decoupled from the rest of LHC upgrade; they would boost luminosity for all LHC stages
global collaboration, synergy with ILC, CLIC & light sources
first prototype beam test expected approximately in
KEKB experience critical
new coupler designs for robust damping needed
collimation, impedance and noise issues require simulations, tests, and developments
LHC would benefit from novel compact cavities

16. Deflecting Cavity Workshop
ICFA Beam Dynamics Mini-Workshop on Deflecting/Crabbing Cavity Applications in Accelerators
April 23-25, 2008 at SINAP, Shanghai
Topics: deflecting/crabbing cavity R&D in the applications of:
high energy colliders (ILC, LHC, KEK-B, CLIC, …)
generation of short x-ray pulse in synchrotron light sources
beam manipulations, emittance exchanges and diagnostics
Yi-Peng Sun will represent HHH
HHH LHC crab cavity day at CERN planned in fall’08