beam-beam effects for lhc and lhc upgrade scenarios
DESCRIPTION
Beam-Beam Effects for LHC and LHC Upgrade Scenarios. Frank Zimmermann US-LARP Beam-Beam Workshop SLAC, 2007. We acknowledge the support of the European Community-Research Infrastructure Activity under the FP6 - PowerPoint PPT PresentationTRANSCRIPT
Electron Lens at the LHCBeam-Beam Effects for LHC and LHC Upgrade
Scenarios
Frank Zimmermann
LHC beam-beam effects
incoherent beam-beam effects
lifetime & dynamic aperture
beam-beam issues in LHC versions
nominal LHC design criterion, head-on collisions, crossing angle, alternating crossing, long-range beam-beam effects, halo collision, tune footprints, dispersion, noise, strong-strong effects
early-separation upgrade crab cavity, low-distance parasitic encounters, crab waist collisions, emittance growth due to crab noise
large Piwinski angle upgrade new regime for hadron colliders, crab waist collisions, tune shift, wire compensation, emittance growth due to wire noise
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
two high luminosity
two lower-luminosity
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
long-range separation at IP1 & 5
T. Sen et al, LHC’99
3 different
crossing angles;
design criterion (J. Gareyte, J.-P. Koutchouk)
avoid resonances < order 13 & |QH-QV|~0.01
→ nominal total tune spread (up to 6s in x&y) from all IPs and over all bunches, including long-range effects, should be less than 0.01-0.012
notes:
6s is empirical to match results of Ritson & Chou
for “ultimate” LHC, |QH-QV|~0.005, and the total tune spread should be less than 0.015-0.017
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
nominal 7-TeV collision parameters
1 halo collision with 5-s separation at IP2
60 long-range collisions with on average ~9.5 separation
60 negligible long-range collisions
“Piwinski angle”
by roughly the same factor
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Hadron Colliders: RHIC operates with crossing angles of +/- 0.5 mrad due to limited BPM resolution and diurnal orbit motion. Performance of proton stores is very irreproducible and frequently occurring lifetime problems could be related to the crossing angle, but this is not definitely proven. [W. Fischer]
Tevatron controls crossing angle to better than 10 mrad, and for angles of 10-20 mrad no lifetime degradation is seen. [V. Shiltsev]
Lepton colliders:
increase in the KEKB beam-beam tune shift limit
by a factor 2-3 for head-on collision compared with
the present crossing angle. This is the primary
motivation for installing crab cavities. [K. Ohmi]
Impact of crossing angle?
Experiment at SPS Collider
“Proton Antiproton Collisions at a
Finite Crossing Angle in the SPS”,
PAC91 San Francisco
head-on tune shift
(with Piwinski angle
tune footprints due to head-on
and long-range collisions in IP1
and IP5 [courtesy H. Grote]
total LHC tune footprint for
regular and PACMAN bunch
DQ from LR collisions is approximately cancelled by alternating crossing
[D. Neuffer, S. Peggs, SSC-63 (1986)]
tune footprints & alternating crossing
“diffusive
aperture”
new regime of hadron beam-beam
with
for nominal LHC: xsep~9.5s, xda~6s
J. Irwin, SSC-223 (1989)
current dependence of dynamic aperture
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
H. Grote, L.H.A. Leunissen, Y. Luo, F. Schmidt
dynamic aperture with beam-beam and field errors
injection 450 GeV
collision 7 TeV
even small field errors lead to losses when beam-beam present;
benefits of triplet correction much reduced
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
recent tune & angle scans
traces of resonances
bunch-to-bunch emittance variation
reduces normalized separation for larger bunches
head-on collisions with unequal beam size will lead to particle losses from larger bunches
→ bunch-to-bunch variation should not exceed 10% (about the best the injectors can do); same tolerance for intensity
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
LHC filling pattern
lack of 4-fold symmetry → some bunches encounter abort gap in IP2 or 8 and have missing head-on collisions; in addition IP8 is displaced by 11.22 m and also 3 bunches in each train miss head-on collisions in IP2
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
All encounters in the straight sections are taken into account. Each bunch in the LHC is represented as a dot. The angular co-ordinate is the initial position of the bunch around the circumference. There is a one-to-one correspondence between beam-beam equivalence class and the radius in the plot. The classes are sorted according to the population of the class. Thus, classes containing a single bunch, of which there are several, lie towards the centre of the plot. Tomake adjacent classes easier to distinguish they are also colored differently (although the colours are used several times over at clearly distinguishable radii).Here there are 171 equivalence classes.
Beam-Beam Equivalence Classes for LHCr [J. Jowett, LHC’99]
only ~half of the bunches
are regular
PACMAN effects
partial compensation by alternating crossing in IP1 and 5
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
bunch-to-bunch orbit variation
collisions are head-on in the other plane;
in addition ground motion ay separate the two beams
by 5s during 8 hours
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
bunch-to-bunch Q, Q’ variation
intermediate comments
alternating crossing ~ kind of beam-beam compensation
vertical dispersion from crossing angle cannot easily be corrected; SBR strength from crossing angle comparable to that from dispersion [H. Leunissen, LHC’99]
alternating crossing vs equal-plane crossing → tune shift & resonance excitation
role of phase advance between IPs
→ LRBB resonance excitation, off-momentum b beating, nonlinear chromaticity
wire compensation (dc, pulsed)
emittance growth from noise
noise sources: ground motion, power converter ripple, transverse feedback, rf, wire compensator, crab cavity
emittance growth due to random beam-beam offset including decoherence and feedback [Y. Alexahin]:
where g is a feedback gain factor (typically g~0.2), |x| the total beam-beam tune-shift parameter assumed equal 0.01, sx* the horizontal IP beam size, nIP the number of IPs (taken to be two), and s0~0.645
emittance growth < 1%/hr:
→ Dx < 2.6 nm for g=0.2, Dx < 0.6 nm for g=0.0
consistent with
simulations by
K. Ohmi
LHC ground motion
“high” frequency
“low” frequency
1.5x LEP
10x LEP
coherent beam-beam effects
unlike SPS and Tevatron, LHC will operate in the strong-strong regime
Y. Alexahin predicted that Landau damping of the p mode may be lost
Landau damping can be restored by symmetry breaking
different intensities
different tunes
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
p mode
s mode
p mode Landau damped
W. Herr, M.P. Zorzano, F. Jones, PRST-AB 4, 054402 (2002)
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Landau damping from beam-beam
strong-strong emittance growth?
coherent beam-beam mode coupling yields instability [A. Chao, R. Ruth, Part.Accel.16:201-216,1985]
together with Landau damping “virtual” instabilities could lead to continuous emittance growth
(A. Chao, private communication)
nominal tune footprint
tune footprint up to 6s
with 2 IPs
intensity
L=1034 cm-2s-1
L=2.3x1034 cm-2s-1
SPS, Tevatron, RHIC experience: beam-beam limit ↔ total tune shift DQ~0.01
going from 4 to 2 IPs we can increase ATLAS&CMS luminosity by factor 2.3
this and all following upgrade studies were based on assumption of only 2 IPs
~0.01
~0.01
~0.01
~0.01
early separation (ES)
Leff [1034 cm-2s-1]
Leff [1034 cm-2s-1]
PSR [W/m]
Pgas [W/m]
0.04 (0.38)
0.06 (0.56)
0.06 (0.56)
0.09 (0.9)
early separation (ES)
squeeze b* to ~10 cm in ATLAS & CMS
add early-separation dipoles in detectors starting at ~ 3 m from IP; accept 4 long-range collisions at 4-5s separation
possibly also add quadrupole-doublet inside detector at ~13 m from IP
and add crab cavities
stronger triplet magnets
b*~25 cm
wire
compensator
Name Event Date*
ES luminosity boost by crab cavities
5s separation
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
RHIC experiments in 2005 and 2006
single off-center collision
one collision with 5-6s offset strongly increases RHIC beam loss rate; worse at smaller offsets
(W. Fischer et al.)
LHC Upgrade Beam Parameters, Frank Zimmermann
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Tevatron 2006
removal of two 5-s collisions at … increased luminosity by 15-30%
(V. Shiltsev)
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Upgrade Option: Flat Beam Collisions
Crossing plane = plane where the beam size is larger at IP (i.e. smaller in the triplet)
To gain aperture in the triplet (smaller crossing angle and better matching between beam-screen and beam aspect ratio, see next slide)
To gain in luminosity (geometric loss factor ~ 1)
Luminosity calculated for two head-on colliding round beams
r.m.s. bunch length (7.5 cm in collision for the nominal LHC)
Full X-angle in s units (9.5 s’* for the nominal LHC)
S. Fartoukh, LHC-MAC, 16 June 2006
flat beams were first proposed by US-LARP,
S. Peggs, T. Sen, et al
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Potential of Flat Beam: Aperture
Triplet beam screen orientation for H/V crossing
Effect of decreasing the
(and increasing the vert. X-angle)
Effect of increasing the
(and decreasing the vert. X-angle)
In all cases, the average
b-b separation is set to
9.5*sx/y (for H/V crossing)
Find the optimum match between
beam-screen and beam aspect ratio
S. Fartoukh, LHC-MAC, 16 June 2006
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Head-on beam-beam for flat beams
independent of r provided inversion of the beam aspect ratio from IR1 to IR5 as in the present case:
S. Fartoukh, LHC-MAC, 16 June 2006
Individual contribution
of the X-angle in the flat beam case)
Nominal :one IR with
for bx* = by* = 55 cm
Flat beam case 4:IR5 contribution IR5 for by* = 88 cm, bx* = 30 cm
Flat beam case 4:IR1 contribution
for bx* = 88 cm, by* = 30 cm
Nominal tune at zero intensity:
(.31/0.32)
Long-range beam-beam for flat beams:
Tune shift only partially compensated by the H/V separation scheme with flat beam:
Beam-beam tune spread and driven resonances further amplified by high b at the parasitic encounters,
e.g. the non-resonant beam-beam driven anharmonicity coefficients scale as
S. Fartoukh, LHC-MAC, 16 June 2006
stronger LR effect should be compensated!
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Beam-beam tune footprint at 6s at nominal intensity for nominal case (blue) compared to two flat beam cases (red)
Flat beam case:
Other flat beam case:
r~1.45, b*~61cm
DQ ~2. 10-2
DQ ~ 1.6 10-2
20% improvement of
tune spread, loosing
After Q-adjustment
After Q-adjustment
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
1’000’000-turn dynamic aperture at nominal intensity for nominal case (blue) and flat beam case (red):
S. Fartoukh, LHC-MAC, 16 June 2006,
Net reduction by ~ 40% from
6-7s to 4-5 s for the min. DA.
No possibility of further improvement via a tiny tune scan.
DA almost exactly follows the change in the b-b tune spread
stronger LR effect must
upgrade option: crab waist
focal plane
summary – LHC b-b compensation
alternating crossing or not?
crab cavity
head-on compensation (EL)
large Piwinski angle
flat beams (easier wire?, crab waists)
hadron beam crab waist
both need
beam test!
Thanks!
Yuri Alexahin, Rama Calaga, Alex Chao, Ulrich Dorda, Stephane Fartoukh, Wolfram Fischer, Jacques Gareyte, Hans Grote, Werner Herr, Albert Hofmann, Wolfgang Hofle, John Irwin, John Jowett, Dobrin Kaltchev, Eberhard Keil, Jean-Pierre Koutchouk, Peter Leunissen, Yun Luo, Kazuhito Ohmi, Katsunobu Oide, Yannis Papaphilippou, Steve Peggs, Dave Ritson,Walter Scandale, Tanaji Sen, Frank Schmidt, Vladimir Shiltsev, Rogelio Tomas, Luc Vos, Jorg Wenninger, Kaoru Yokoya, Xiaolong Zhang, Maria-Paz Zorzano, …
LHC Upgrade Beam Parameters, Frank Zimmermann
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
some references
J. Poole and F. Zimmermann, eds., Proceedings of Workshop on beam-beam effects in Large Hadron Colliders, CERN/SL 99-039 (AP) (1999).
J. Gareyte, Beam-Beam Design Criteria for LHC, Proc. LHC’99
O. Bruning et al, LHC Design Report, Vol. 1, Chapter 5 (beam-beam section by W. Herr), CERN-2004-003
Y. Alexahin, On the Landau damping and decoherence of transverse dipole oscillations in colliding beams, Part. Accel. 59, 43 (1998).
W. Chou and D. Ritson, Dynamic aperture studies during collisions in the LHC, CERN LHC Project Report 123 (1997).
L. Leunissen, Influence of vertical dispersion and crossing angle on the performance of the LHC, CERN LHC Project Report 298 (1999).
Y. Papaphilippou, F. Zimmermann, Weak-strong beam-beam simulations for the Large Hadron Collider, PRST-AB 2:104001, 1999
Y. Papaphilippou & F. Zimmermann, Estimates of diffusion due to long-range beam-beam collisions, PRST-AB 5:074001, 2002.
M.P. Zorzano, F. Zimmermann, Coherent beam-beam oscillations at the LHC, PRST-AB 3:044401, 2000.
W. Herr, M.P. Zorzano and F. Jones A Hybrid Fast Multipole Method applied to beam-beam collisions in the strong strong regime, PRST-AB 4, 054402 (2001)
H. Grote, L. Leunissen, F. Schmidt, LHC Dynamic Aperture at Collision, LHC Project Note 197 (1999).
J. Jowett, Collision Schedules and Bunch Filling Schemes in the LHC, CERN LHC Project Note 179 (1999).
M.P.Zorzano, T.Sen, Emittance growth for the LHC beams due to head-on beam-beam interaction and ground motion , LHC Project Note 222 (2000).
W. Herr, L. Vos, Tune distributions and effective tune spread from beam-beam interactions and the consequences for Landau damping in the LHC, LHC Project Note 316, 2003
W. Herr, M.-P. Zorzano, Coherent Dipole Modes for Multiple Interaction Regions, LHC Project Report 462 (2001)
Y. Alexahin, A study of the Coherent Beam-Beam Effect in the framework of the Vlasov Perturbation Theory, NIM A 380, 253 (2002)
W. Herr, R. Paparella, Landau Damping of Coherent Modes by Overlap with Synchrotron Sidebands, CERN LHC Project Note 304, 2002
W. Herr, Features and Implications of Different LHC Crosing Schemes, LHC Project Report 628 (2003)
Y. Alexahin, On the Emittance Growth due to Noise in Hadron Colliders and Methods of its Suppression, NIM A 391, 73 (1996).
cm
10
Frank Zimmermann
LHC beam-beam effects
incoherent beam-beam effects
lifetime & dynamic aperture
beam-beam issues in LHC versions
nominal LHC design criterion, head-on collisions, crossing angle, alternating crossing, long-range beam-beam effects, halo collision, tune footprints, dispersion, noise, strong-strong effects
early-separation upgrade crab cavity, low-distance parasitic encounters, crab waist collisions, emittance growth due to crab noise
large Piwinski angle upgrade new regime for hadron colliders, crab waist collisions, tune shift, wire compensation, emittance growth due to wire noise
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
two high luminosity
two lower-luminosity
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
long-range separation at IP1 & 5
T. Sen et al, LHC’99
3 different
crossing angles;
design criterion (J. Gareyte, J.-P. Koutchouk)
avoid resonances < order 13 & |QH-QV|~0.01
→ nominal total tune spread (up to 6s in x&y) from all IPs and over all bunches, including long-range effects, should be less than 0.01-0.012
notes:
6s is empirical to match results of Ritson & Chou
for “ultimate” LHC, |QH-QV|~0.005, and the total tune spread should be less than 0.015-0.017
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
nominal 7-TeV collision parameters
1 halo collision with 5-s separation at IP2
60 long-range collisions with on average ~9.5 separation
60 negligible long-range collisions
“Piwinski angle”
by roughly the same factor
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Hadron Colliders: RHIC operates with crossing angles of +/- 0.5 mrad due to limited BPM resolution and diurnal orbit motion. Performance of proton stores is very irreproducible and frequently occurring lifetime problems could be related to the crossing angle, but this is not definitely proven. [W. Fischer]
Tevatron controls crossing angle to better than 10 mrad, and for angles of 10-20 mrad no lifetime degradation is seen. [V. Shiltsev]
Lepton colliders:
increase in the KEKB beam-beam tune shift limit
by a factor 2-3 for head-on collision compared with
the present crossing angle. This is the primary
motivation for installing crab cavities. [K. Ohmi]
Impact of crossing angle?
Experiment at SPS Collider
“Proton Antiproton Collisions at a
Finite Crossing Angle in the SPS”,
PAC91 San Francisco
head-on tune shift
(with Piwinski angle
tune footprints due to head-on
and long-range collisions in IP1
and IP5 [courtesy H. Grote]
total LHC tune footprint for
regular and PACMAN bunch
DQ from LR collisions is approximately cancelled by alternating crossing
[D. Neuffer, S. Peggs, SSC-63 (1986)]
tune footprints & alternating crossing
“diffusive
aperture”
new regime of hadron beam-beam
with
for nominal LHC: xsep~9.5s, xda~6s
J. Irwin, SSC-223 (1989)
current dependence of dynamic aperture
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
H. Grote, L.H.A. Leunissen, Y. Luo, F. Schmidt
dynamic aperture with beam-beam and field errors
injection 450 GeV
collision 7 TeV
even small field errors lead to losses when beam-beam present;
benefits of triplet correction much reduced
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
recent tune & angle scans
traces of resonances
bunch-to-bunch emittance variation
reduces normalized separation for larger bunches
head-on collisions with unequal beam size will lead to particle losses from larger bunches
→ bunch-to-bunch variation should not exceed 10% (about the best the injectors can do); same tolerance for intensity
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
LHC filling pattern
lack of 4-fold symmetry → some bunches encounter abort gap in IP2 or 8 and have missing head-on collisions; in addition IP8 is displaced by 11.22 m and also 3 bunches in each train miss head-on collisions in IP2
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
All encounters in the straight sections are taken into account. Each bunch in the LHC is represented as a dot. The angular co-ordinate is the initial position of the bunch around the circumference. There is a one-to-one correspondence between beam-beam equivalence class and the radius in the plot. The classes are sorted according to the population of the class. Thus, classes containing a single bunch, of which there are several, lie towards the centre of the plot. Tomake adjacent classes easier to distinguish they are also colored differently (although the colours are used several times over at clearly distinguishable radii).Here there are 171 equivalence classes.
Beam-Beam Equivalence Classes for LHCr [J. Jowett, LHC’99]
only ~half of the bunches
are regular
PACMAN effects
partial compensation by alternating crossing in IP1 and 5
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
bunch-to-bunch orbit variation
collisions are head-on in the other plane;
in addition ground motion ay separate the two beams
by 5s during 8 hours
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
bunch-to-bunch Q, Q’ variation
intermediate comments
alternating crossing ~ kind of beam-beam compensation
vertical dispersion from crossing angle cannot easily be corrected; SBR strength from crossing angle comparable to that from dispersion [H. Leunissen, LHC’99]
alternating crossing vs equal-plane crossing → tune shift & resonance excitation
role of phase advance between IPs
→ LRBB resonance excitation, off-momentum b beating, nonlinear chromaticity
wire compensation (dc, pulsed)
emittance growth from noise
noise sources: ground motion, power converter ripple, transverse feedback, rf, wire compensator, crab cavity
emittance growth due to random beam-beam offset including decoherence and feedback [Y. Alexahin]:
where g is a feedback gain factor (typically g~0.2), |x| the total beam-beam tune-shift parameter assumed equal 0.01, sx* the horizontal IP beam size, nIP the number of IPs (taken to be two), and s0~0.645
emittance growth < 1%/hr:
→ Dx < 2.6 nm for g=0.2, Dx < 0.6 nm for g=0.0
consistent with
simulations by
K. Ohmi
LHC ground motion
“high” frequency
“low” frequency
1.5x LEP
10x LEP
coherent beam-beam effects
unlike SPS and Tevatron, LHC will operate in the strong-strong regime
Y. Alexahin predicted that Landau damping of the p mode may be lost
Landau damping can be restored by symmetry breaking
different intensities
different tunes
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
p mode
s mode
p mode Landau damped
W. Herr, M.P. Zorzano, F. Jones, PRST-AB 4, 054402 (2002)
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Landau damping from beam-beam
strong-strong emittance growth?
coherent beam-beam mode coupling yields instability [A. Chao, R. Ruth, Part.Accel.16:201-216,1985]
together with Landau damping “virtual” instabilities could lead to continuous emittance growth
(A. Chao, private communication)
nominal tune footprint
tune footprint up to 6s
with 2 IPs
intensity
L=1034 cm-2s-1
L=2.3x1034 cm-2s-1
SPS, Tevatron, RHIC experience: beam-beam limit ↔ total tune shift DQ~0.01
going from 4 to 2 IPs we can increase ATLAS&CMS luminosity by factor 2.3
this and all following upgrade studies were based on assumption of only 2 IPs
~0.01
~0.01
~0.01
~0.01
early separation (ES)
Leff [1034 cm-2s-1]
Leff [1034 cm-2s-1]
PSR [W/m]
Pgas [W/m]
0.04 (0.38)
0.06 (0.56)
0.06 (0.56)
0.09 (0.9)
early separation (ES)
squeeze b* to ~10 cm in ATLAS & CMS
add early-separation dipoles in detectors starting at ~ 3 m from IP; accept 4 long-range collisions at 4-5s separation
possibly also add quadrupole-doublet inside detector at ~13 m from IP
and add crab cavities
stronger triplet magnets
b*~25 cm
wire
compensator
Name Event Date*
ES luminosity boost by crab cavities
5s separation
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
RHIC experiments in 2005 and 2006
single off-center collision
one collision with 5-6s offset strongly increases RHIC beam loss rate; worse at smaller offsets
(W. Fischer et al.)
LHC Upgrade Beam Parameters, Frank Zimmermann
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Tevatron 2006
removal of two 5-s collisions at … increased luminosity by 15-30%
(V. Shiltsev)
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Upgrade Option: Flat Beam Collisions
Crossing plane = plane where the beam size is larger at IP (i.e. smaller in the triplet)
To gain aperture in the triplet (smaller crossing angle and better matching between beam-screen and beam aspect ratio, see next slide)
To gain in luminosity (geometric loss factor ~ 1)
Luminosity calculated for two head-on colliding round beams
r.m.s. bunch length (7.5 cm in collision for the nominal LHC)
Full X-angle in s units (9.5 s’* for the nominal LHC)
S. Fartoukh, LHC-MAC, 16 June 2006
flat beams were first proposed by US-LARP,
S. Peggs, T. Sen, et al
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Potential of Flat Beam: Aperture
Triplet beam screen orientation for H/V crossing
Effect of decreasing the
(and increasing the vert. X-angle)
Effect of increasing the
(and decreasing the vert. X-angle)
In all cases, the average
b-b separation is set to
9.5*sx/y (for H/V crossing)
Find the optimum match between
beam-screen and beam aspect ratio
S. Fartoukh, LHC-MAC, 16 June 2006
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Head-on beam-beam for flat beams
independent of r provided inversion of the beam aspect ratio from IR1 to IR5 as in the present case:
S. Fartoukh, LHC-MAC, 16 June 2006
Individual contribution
of the X-angle in the flat beam case)
Nominal :one IR with
for bx* = by* = 55 cm
Flat beam case 4:IR5 contribution IR5 for by* = 88 cm, bx* = 30 cm
Flat beam case 4:IR1 contribution
for bx* = 88 cm, by* = 30 cm
Nominal tune at zero intensity:
(.31/0.32)
Long-range beam-beam for flat beams:
Tune shift only partially compensated by the H/V separation scheme with flat beam:
Beam-beam tune spread and driven resonances further amplified by high b at the parasitic encounters,
e.g. the non-resonant beam-beam driven anharmonicity coefficients scale as
S. Fartoukh, LHC-MAC, 16 June 2006
stronger LR effect should be compensated!
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
Beam-beam tune footprint at 6s at nominal intensity for nominal case (blue) compared to two flat beam cases (red)
Flat beam case:
Other flat beam case:
r~1.45, b*~61cm
DQ ~2. 10-2
DQ ~ 1.6 10-2
20% improvement of
tune spread, loosing
After Q-adjustment
After Q-adjustment
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
1’000’000-turn dynamic aperture at nominal intensity for nominal case (blue) and flat beam case (red):
S. Fartoukh, LHC-MAC, 16 June 2006,
Net reduction by ~ 40% from
6-7s to 4-5 s for the min. DA.
No possibility of further improvement via a tiny tune scan.
DA almost exactly follows the change in the b-b tune spread
stronger LR effect must
upgrade option: crab waist
focal plane
summary – LHC b-b compensation
alternating crossing or not?
crab cavity
head-on compensation (EL)
large Piwinski angle
flat beams (easier wire?, crab waists)
hadron beam crab waist
both need
beam test!
Thanks!
Yuri Alexahin, Rama Calaga, Alex Chao, Ulrich Dorda, Stephane Fartoukh, Wolfram Fischer, Jacques Gareyte, Hans Grote, Werner Herr, Albert Hofmann, Wolfgang Hofle, John Irwin, John Jowett, Dobrin Kaltchev, Eberhard Keil, Jean-Pierre Koutchouk, Peter Leunissen, Yun Luo, Kazuhito Ohmi, Katsunobu Oide, Yannis Papaphilippou, Steve Peggs, Dave Ritson,Walter Scandale, Tanaji Sen, Frank Schmidt, Vladimir Shiltsev, Rogelio Tomas, Luc Vos, Jorg Wenninger, Kaoru Yokoya, Xiaolong Zhang, Maria-Paz Zorzano, …
LHC Upgrade Beam Parameters, Frank Zimmermann
Frank Zimmermann, LARP Beam-Beam, SLAC, July 2077
some references
J. Poole and F. Zimmermann, eds., Proceedings of Workshop on beam-beam effects in Large Hadron Colliders, CERN/SL 99-039 (AP) (1999).
J. Gareyte, Beam-Beam Design Criteria for LHC, Proc. LHC’99
O. Bruning et al, LHC Design Report, Vol. 1, Chapter 5 (beam-beam section by W. Herr), CERN-2004-003
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