LHC beam performance and luminosity upgrade scenarios

1
LHC beam performance and luminosity upgrade
scenarios

• performance limitations, possible scenarios and
  milestones for the LHC upgrade

triplet magnets
BBLR
http//care-hhh.web.cern.ch/care-hhh/
See also slides on Measurements, ideas,
curiosities
2
Outline

• Time scale and potential of an LHC upgrade
• LHC commissioning strategy and beam parameters
• Machine performance limitations
• Luminosity optimization and upgrade paths
• Luminosity lifetime peak vs integrated
  luminosity
• LHC luminosity upgrade scenarios
• ultimate performance without hardware changes
• upgrade of the Interaction Regions
• new bunch-shortening RF system and cryogenic
  loads
• collimation, beam-beam compensation and crab
  cavities
• milestones and baseline design

3
Time scale of an LHC upgrade
radiation damage limit 700 fb-1
time to halve error
integrated L
L at end of year
ultimate luminosity
design luminosity
courtesy J. Strait

• the life expectancy of LHC IR quadrupole magnets
  is estimated to be lt10 years owing to high
  radiation doses
• the statistical error halving time will exceed 5
  years by 2011-2012
• therefore, it is reasonable to plan a machine
  luminosity upgrade based on new low-ß IR magnets
  before 2015

4
luminosity versus energy upgrade
Courtesy of Michelangelo Mangano
5
Chronology of LHC Upgrade studies

• Summer 2001 two CERN task forces investigate
  physics potential (CERN-TH-2002-078) and
  accelerator aspects (LHC Project Report 626) of
  an LHC upgrade by a factor 10 in luminosity and
  2-3 in energy
• March 2002 LHC IR Upgrade collaboration meeting
  
• http//cern.ch/lhc-proj-
  IR-upgrade
• October 2002 ICFA Seminar at CERN on
• Future Perspectives in
  High Energy Physics
• 2003 US LHC Accelerator Research Program (LARP)
• 2004 CARE-HHH European Network on High Energy
  
  High Intensity
  Hadron
  Beams
• November 2004 first CARE-HHH-APD Workshop
  (HHH-04) on
• Beam Dynamics in
  Future Hadron Colliders and Rapidly
• Cycling High-Intensity
  Synchrotrons, CERN-2005-006
• September 2005 CARE-HHH Workshop (LHC-LUMI-05)
  on
• Scenarios for the LHC
  Luminosity Upgrade
• http//care-hhh.web.
  cern.ch/CARE-HHH/LUMI-05/

6
The CARE-HHH Network
Mandate
Coordinate and integrate the activities of the
accelerator and particle physics communities, in
a worldwide context, towards achieving superior
High-Energy High-Intensity Hadron-Beam facilities
for Europe

• Roadmap for the upgrade of the European
  accelerator infrastructure (LHC and GSI
  accelerator complex)
• luminosity and energy upgrade for the LHC
• pulsed SC high intensity synchrotrons for the GSI
  and LHC complex
• RD and experimental studies at existing hadron
  accelerators
• select and develop technologies providing viable
  design options
• Coordinate activities and foster future
  collaborations
• Disseminate information

• HHH coordination F. Ruggiero (CERN) W.
  Scandale (CERN)
• Advancement in Acc. Magnet Technology (AMT) L.
  Rossi (CERN) L. Bottura (CERN)
• Novel Meth. for Acc. Beam Instrumentation (ABI)
  H. Schmickler (CERN) K. Wittenburg (DESY)
• Accelerator Physics and Synchrotron Design (APD)
  F. Ruggiero (CERN) F. Zimmermann (CERN)

7
Nominal LHC parameters
collision energy dipole peak field injection energy Ecm B Einj 2x7 8.3 450 TeV T GeV
protons per bunch bunch spacing average beam current Nb ?t I 1.15 25 0.58 1011 ns A
stored energy per beam radiated power per beam 362 3.7 MJ kW
normalized emittance rms bunch length ?n ?z 3.75 7.55 mm cm
beam size at IP1IP5 beta function at IP1IP5 full crossing angle s b ?c 16.6 0.55 285 ?m m ?rad
luminosity lifetime peak luminosity events per bunch crossing ?L L 15.5 1034 19.2 h cm-2s-1
integrated luminosity ? L dt 66.2 fb-1/year
8
LHC upgrade paths/limitations

• Peak luminosity at the beam-beam limit L I/b
• Total beam intensity I limited by electron cloud,
  collimation, injectors
• Minimum crossing angle depends on beam intensity
  limited by triplet aperture
• Longer bunches allow higher bb-limit for Nb/en
  limited by the injectors
• Less ecloud and RF heating for longer bunches
  50 luminosity gain for flat bunches longer than
  b
• Event pile-up in the physics detectors increases
  with Nb
• Luminosity lifetime at the bb limit depends only
  on b ? reduce Tturnaround to increase integrated
  lumi

longer bunches
larger crossing angle
I1.72 A
I0.86 A
ultimate
bb limit
more bunches
I0.58 A
nominal
9
Expected factors for the LHC luminosity upgrade

• The peak LHC luminosity can be multiplied by
• factor 2.3 from nominal to ultimate beam
  intensity (0.58 ? 0.86 A)
• factor 2 (or more?) from new low-beta insertions
  with ß 0.25 m
• Tturnaround10 h ? ?Ldt 3 x nominal
  200/(fbyear)

• Major hardware upgrades (LHC main ring and
  injectors) are needed to exceed ultimate beam
  intensity. The peak luminosity can be increased
  by
• factor 2 if we can double the number of bunches
  (maybe impossible due to electron cloud effects)
  or increase bunch intensity and bunch length
• Tturnaround10 h ? ?Ldt 6 x nominal
  400/(fbyear)

• Increasing the LHC injection energy to 1 TeV
  would potentially yield
• factor 2 in peak luminosity (2 x bunch intensity
  and 2 x emittance)
• factor 1.4 in integrated luminosity from shorter
  Tturnaround5 h
• thus ensuring L1035 cm-2 s-1 and ?Ldt 9 x
  nominal 600/(fbyear)

10
Challenge of a Cold Machine
11
LHC Cleaning System (R. Assmann)
Two-stage cleaning (phase 2)
Two-stage cleaning (phase 1)
43
Single-stage cleaning
No collimation
Pilot
12
Collimation Machine Protection
13
Constraints for LHC commissioning

• Only 8/20 LHC dump dilution kickers available
  during the first two years of operation ? total
  beam intensity in each LHC ring limited to 1/2 of
  its nominal value
• According to SPS experience and to electron cloud
  simulations, the initial LHC bunch intensity Nb
  can reach and possibly exceed its nominal value
  for 75 ns bunch spacing, while it may be limited
  to about 1/3 of its nominal value for 25 ns
  spacing
• Machine protection and collimation favours
  initial operation with lower beam power and lower
  transverse beam density. Simple graphite
  collimators may limit maximum transverse energy
  density to about 1/2 of its nominal value
• Emittance preservation from injection to physics
  conditions will require a learning curve ? do not
  assume transverse emittance smaller than nominal,
  even for reduced bunch intensity
• Initial operation with relaxed parameters is
  strongly favoured ? higher ß, reduced crossing
  angle, and fewer parasitic collisions

14
LHC beam commissioningMike Lamont, Chamonix 2005
workshop
43 on 43 with 3 to 4 x 1010 ppb to 7 TeV

• No parasitic encounters
• No crossing angle
• No long range beam-beam
• Larger aperture
• Instrumentation
• Good beam for RF, Vacuum
• Lower energy densities
• Reduced demands on beam dump system
• Collimation
• Machine protection
• Luminosity
• 1030 cm-2s-1 at 18 m
• 2 x 1031 cm-2s-1 at 1 m

15
LHC beam commissioningMike Lamont, Chamonix 2005
workshop
Phase R1/2 Time days Total
1 Injection 2 1 2
2 First turn 2 3 6
3 Circulating beam 2 3 6
4 450 GeV initial commissioning 2 4 8
5 450 GeV detailed measurements 2 4 8
6 450 GeV 2 beams 1 2 2
7 Nominal cycle 1 5 5
8 Snapback single beam 2 3 6
9 Ramp single beam 2 4 8
10 Single beam to physics energy 2 2 4
11 Two beams to physics energy 1 3 3
12 Establish Physics 1 2 2
13 Commission squeeze 2 4 4
14 Physics partially squeezed
TOTAL 60
16
Steps to reach nominal LHC luminosity
parameter units 75 ns spacing 25 ns spacing nominal
number of bunches protons per bunch nb Nb 1011 936 0.9 2808 0.4 2808 1.15
normalized emittance rms bunch length rms energy spread ?n µm ?z cm ?E 10-4 3.75 7.55 1.13 3.75 7.55 1.13 3.75 7.55 1.13
IBS growth time beta at IP full crossing angle ?xIBS h ß m ?c ?rad 135 1.0 250 304 0.55 285 106 0.55 285
luminosity lifetime peak luminosity events per crossing ?L h L 1034cm-2s-1 22 0.12 7.1 26 0.12 2.3 15 1.0 19.2
? over 200 runs L dt Lint fb-1 9.3 9.5 66.2
Possible scenarios with 75 ns and 25 ns bunch
spacing for early LHC runs with integrated
luminosity of about 10 fb-1 in 200 fills,
assuming an average physics run time Trun 14 h
and Tturnaround10 h.
17
Luminosity optimization
transverse beam size at IP
normalized emittance
peak luminosity for head-on collisions round
beams, short Gaussian bunches

• I nbfrevNb total beam current
• long range beam-beam
• collective instabilities
• synchrotron radiation
• stored beam energy

• Nb/en beam brightness
• head-on beam-beam
• space-charge in the injectors
• transfer dilution

• Collisions with full crossing angle qc
• reduce luminosity by a geometric factor F
• maximum luminosity below beam-beam limit
• ? short bunches and minimum crossing angle
  (baseline scheme)
• H-V crossings in two IPs ? no linear tune shift
  due to long range
• total linear bb tune shift also reduced by F

18

• If bunch intensity and brightness are not limited
  by the injectors
• or by other effects in the LHC (e.g. electron
  cloud) ? luminosity
• can be increased without exceeding beam-beam
  limit DQbb0.01
• by increasing the crossing angle and/or the bunch
  length
• Express beam-beam limited brilliance Nb/en in
  terms of maximum
• total beam-beam tune shift DQbb, then

At high beam intensities or for large emittances,
the performance will be limited by the angular
triplet aperture
19
Minimum crossing angle

• Beam-Beam Long-Range collisions
• perturb motion at large betatron amplitudes,
  where particles come close to opposing beam
• cause diffusive (or dynamic) aperture, high
  background, poor beam lifetime
• increasing problem for SPS, Tevatron, LHC, i.e.,
  for operation with larger of bunches

dynamic aperture caused by npar parasitic
collisions around two IPs
higher beam intensities or smaller b require
larger crossing angles to preserve dynamic
aperture and shorter bunches to avoid geometric
luminosity loss ? baseline scaling qc1/vb ,
szb
angular beam divergence at IP
20
Schematic of a super-bunch collision, consisting
of head-on and long-range components. The
luminosity for long bunches having flat
longitudinal distribution is 1.4 times higher
than for conventional Gaussian bunches with the
same beam-beam tune shift and identical bunch
population (see LHC Project Report 627)
21
Schematic of reduced electron cloud build up for
a long bunch. Most electrons do not gain any
energy when traversing the chamber in the
quasi-static beam potential
negligible heat load
after V. Danilov
22
Scenarios for the luminosity upgrade

• ultimate performance without hardware changes
  (phase 0)
• maximum performance with only IR changes (phase
  1)
• maximum performance with major hardware changes
  (phase 2)

• Phase 0 steps to reach ultimate performance
  without hardware changes
• collide beams only in IP1 and IP5 with
  alternating H-V crossing
• increase Nb up to the beam-beam limit ? L 2.3 x
  1034 cm-2 s-1
• increase the dipole field to 9T (ultimate field)
  ? Emax 7.54 TeV
• The ultimate dipole field of 9 T corresponds to a
  beam current limited by
• cryogenics and/or by beam dump/machine protection
  considerations.

23
Scenarios for the luminosity upgrade

• Phase 1 steps to reach maximum performance with
  only IR changes
• Modify the insertion quadrupoles and/or layout ?
  ß 0.25 m
• Increase crossing angle ?c by v2 ? ?c 445 µrad
• Increase Nb up to ultimate intensity ? L 3.3 x
  1034 cm-2s-1
• Halve ?z with high harmonic RF system ? L 4.6
  x 1034 cm-2s-1
• Double the no. of bunches nb (and increase ?c ) ?
  L 9.2 x 1034 cm-2s-1
• excluded by electron cloud? Step 5
  belongs to Phase 2

• ? Step 4) requires a new RF system providing
• an accelerating voltage of 43 MV at 1.2 GHz
• a power of about 11 MW/beam
• longitudinal beam emittance reduced to 1.8 eVs
• horizontal Intra-Beam Scattering (IBS) growth
  time decreases by v2

• ? Operational consequences of step 5) ? exceeding
  ultimate beam intensity
• upgrade LHC cryogenics, collimation, RF and beam
  dump systems
• the electronics of all LHC beam position
  monitors should be upgraded
• possibly upgrade SPS RF system and other
  equipment in the injectors

24
luminosity upgrade baseline scheme
1.0
0.58 A
reduce sz by factor 2 using higher frf lower
e (larger qc ?)
qcgtqmindue to LR-bb
increase Nb
restore F
BBLR compen-sation
bb limit?
or decouple L and F
crab cavities
reduce qc (squeeze b)
no
0.86 A
yes
2.3
reduce b by factor 2
new IR magnets
use large qc pass each beam through
separate magnetic channel
4.6
0.86 A
if e-cloud, dump impedance ok
increase nb by factor 2
simplified IR design with large qc

9.2
peak luminosity gain
1.72 A
beam current
25
luminosity upgrade Piwinski scheme
decrease F
reduce b by factor 2
new IR magnets
1.0
increase szqc
0.58 A
superbunches?
flatten profile?
increase Nb
reduce bunches to limit total current?
yes
no
7.7
15.5
luminosity gain
?
0.86 A
1.72 A
beam current
26
Various LHC upgrade options
parameter symbol nominal ultimate shorter bunch longer bunch
no of bunches nb 2808 2808 5616 936
proton per bunch Nb 1011 1.15 1.7 1.7 6.0
bunch spacing ?tsep ns 25 25 12.5 75
average current I A 0.58 0.86 1.72 1.0
normalized emittance ?n µm 3.75 3.75 3.75 3.75
longit. profile Gaussian Gaussian Gaussian flat
rms bunch length ?z cm 7.55 7.55 3.78 14.4
ß at IP1IP5 ß m 0.55 0.50 0.25 0.25
full crossing angle ?c µrad 285 315 445 430
Piwinski parameter ?c ?z/(2?) 0.64 0.75 0.75 2.8
peak luminosity L 1034 cm-2 s-1 1.0 2.3 9.2 8.9
events per crossing 19 44 88 510
luminous region length ?lum mm 44.9 42.8 21.8 36.2
27
Heat loads per beam aperture for various LHC
upgrade options
parameter symbol nominal ultimate shorter bunch longer bunch
protons per bunch Nb 1011 1.15 1.7 1.7 6.0
bunch spacing ?tsepns 25 25 12.5 75
average current I A 0.58 0.86 1.72 1.0
longitudinal profile Gaussian Gaussian Gaussian flat
rms bunch length ?z cm 7.55 7.55 3.78 14.4
Average electron-cloud heat load at 4.620 K in the arc for R50 and dmax1.4 (in parentheses for dmax1.3) Pecloud W /m 1.07 (0.44) 1.04 (0.59) 13.34 (7.85) 0.26 (0.26)
Synchrotron radiation heat load at 4.620 K Pg W /m 0.17 0.25 0.50 0.29
Image currents power at 4.620 K PW W /m 0.15 0.33 1.87 0.96
Beam-gas scattering heat load at 1.9 K for 100-h beam lifetime (in parentheses for a 10-h lifetime). It is assumed that elastic scattering (40 of the total cross section) leads to local loss. Pgas W /m 0.038 (0.38) 0.056 (0.56) 0.113 (1.13) 0.066 (0.66)
28
Events per bunch crossing and beam lifetime due
to nuclear p-p collisions
sbb60 mb total inelastic cross section
beam intensity halving time due to nuclear
p-p collisions at two IPs with total cross
section sTOT110 mb
nuclear scattering lifetime at the
beam-beam limit depends only on b !
luminosity lifetime assumes radiation
damping compensates diffusion
exponential luminosity lifetime due to
nuclear p-p interactions
29
Optimum run time and effective luminosity
The optimum run time and the effective luminosity
are universal functions of Tturnaround/tL
When the beam lifetime is dominated by nuclear
proton-proton collisions, then tLtN/1.54 and the
effective luminosity is a universal functions of
Tturnaround/b
30
Effective luminosity for various upgrade options
parameter symbol nominal ultimate shorter bunch longer bunch
protons per bunch Nb 1011 1.15 1.7 1.7 6.0
bunch spacing ?tsep ns 25 25 12.5 75
average current I A 0.58 0.86 1.72 1.0
longitudinal profile Gaussian Gaussian Gaussian flat
rms bunch length ?z cm 7.55 7.55 3.78 14.4
ß at IP1IP5 ß m 0.55 0.50 0.25 0.25
full crossing angle ?c µrad 285 315 445 430
Piwinski parameter ?c ?z/(2?) 0.64 0.75 0.75 2.8
peak luminosity L 1034 cm-2 s-1 1.0 2.3 9.2 8.9
events per crossing 19 44 88 510
IBS growth time txIBS h 106 72 42 75
nuclear scatt. lumi lifetime tN/1.54 h 26.5 17 8.5 5.2
luminosity lifetime (tgas 85 h) tL h 15.5 11.2 6.5 4.5
effective luminosity Leff 1034 cm-2 s-1 0.4 0.8 2.4 1.9
(Tturnaround10 h) Trun h optimum 14.6 12.3 8.9 7.0
effective luminosity Leff 1034 cm-2 s-1 0.5 1.0 3.3 2.7
(Tturnaround 5 h) Trun h optimum 10.8 9.1 6.7 5.4
31
Interaction Region upgrade
goal reduce b by at least a factor 2
options NbTi cheap upgrade, NbTi(Ta), Nb3Sn
new quadrupoles new
separation dipoles
maximize magnet aperture, minimize distance to IR

• factors driving IR design
• minimize b
• minimize effect of LR collisions
• large radiation power directed towards the IRs
• accommodate crab cavities and/or beam-beam
  compensators. Local Q compensation scheme?
• compatibility with upgrade path

32
IR baseline schemes
crab cavity
triplet magnets
triplet magnets
BBLR
short bunches minimum crossing angle BBLR
crab cavities large crossing angle
33
alternative IR schemes
dipole magnets
dipole
triplet magnets
triplet magnets
dipole first small crossing angle
dipole first large crossing angle long
bunches or crab cavities
reduced LR collisions collision debris hit D1
34
(No Transcript)
35
Dipoles first and doublet focusing

• Features
• Requires beams to be in
• separate focusing channels
• Fewer magnets
• Beams are not round at the IP
• Polarity of Q1 determined by
• crossing plane larger beam
• size in the crossing plane to
• increase overlap
• Opposite polarity focusing at other
• IR to equalize beam-beam tune shifts
• Significant changes to outer triplet
• magnets in matching section.

Q1
D2
Q2
IP
D1
D2
Focusing symmetric about IP
Tanaji Sen, Doublet optics
36
Flat beams

• Interesting approach, flat beams could increase
  luminosity by 20-30 with reduced crossing angle
• Symmetric doublets studied by J. Johnstone (FNAL)
  require separate magnetic channels, i.e.
  dipole-first, Crab cavities or special quads
• Tune footprints are broader than for round beams,
  since there is only partial compensation of
  parasitic beam-beam encounters by the H/V
  crossing scheme. More work needed to evaluate
  nonlinear resonance excitation.
• Probably requires BBLR compensation
• Recently S. Fartoukh has found a more interesting
  flat beam solution with anti-symmetric LHC
  baseline triplets

37
Beam aspect ratio vs triplet aperture (1/5)

• Beam screen orientation for H/V scheme

• In both cases, H-separation of
• about 9.5max(sx,b1 ,sx,b2)

Effect of decreasing the beam aspect ratio at the
IP (and increasing the vert. X-angle)

• In both cases, V-separation of
• about 9.5max(sy,b1 ,sy,b2)

Effect of increasing the beam aspect ratio at the
IP (and decreasing the vert. X-angle)

• Find the optimum matching between
• beam-screen and beam aspect ratio

S. Fartoukh, ABP-RLC meeting, 28-10-2005
38
Pushing the luminosity by 10-20
Case bx cm by cm a mrad n1 in the triplet Geometric loss factor L/Lnom
Nominal r1.0, b55cm 55.00 55.00 285 7 83.9 1.00
Flat r2.0, b55cm 110.00 27.50 201 7 95.1 1.13
Flat r1.6, b55cm 88.00 34.37 225 7.5 92.7 1.10
Flat r1.7, b51cm 88.00 30.00 225 7 92.7 1.18

• All these cases being allowed by the nominal LHC
  hardwarelayout,
• power supply, optics antisymmetry, b.s.
  orientation in the triplets
• (only changing the present H/V scheme into V/H
  scheme)!

S. Fartoukh, ABP-RLC meeting, 28-10-2005
39
cheap IR upgrade
in case we need to double LHC luminosity earlier
than foreseen
triplet magnets
BBLR
short bunches minimum crossing angle BBLR
each quadrupole individually optimized (length
aperture) reduced IP-quad distance from 23 to 22
m conventional NbTi technology b0.25 m is
possible
40
Several LHC IR upgrade options are being explored

• quadrupole-first and dipole-first solutions based
  on conventional NbTi technology and on high-field
  Ni3Sn magnets, possibly with structured SC cable
• energy deposition, absorbers, and quench limits
• schemes with Crab cavities as an alternative to
  the baseline bunch shortening RF system at 1.2
  GHz to avoid luminosity loss with large crossing
  angles
• early beam separation by a D0 dipole located a
  few metres away from the IP (or by tilted
  experimental solenoids?) may allow operation with
  a reduced crossing angle. Open issues
  compatibility with detector layout, reduced
  separation at first parasitic encounters, energy
  deposition by the collision debris
• local chromaticity correction schemes
• flat beams, i.e. a final doublet instead of a
  triplet. Open issues compensation of long range
  beam-beam effects with alternating crossing planes

41
Crab cavities vs bunch shortening
Comparison of timing tolerances
KEKB Super-KEKB ILC Super-LHC
sx 100 mm 70 mm 0.24 mm 11 mm
qc /- 11 mrad /-15 mrad /-5 mrad /- 0.5 mrad
Dt 6 ps 3 ps 0.03 ps 0.08 ps

• Crab cavities combine advantages
• of head-on collisions and large
• crossing angles
• require lower voltages compared
• to bunch shortening RF systems
• but tight tolerance on phase jitter
• to avoid emittance growth

42
Crab Cavities
43
Motivation of Beam-Beam compensation studies

• Provide more LHC luminosity earlier
• Space is reserved in the LHC for the wires.
  An early test in RHIC will determine the
  effectiveness of the compensation and possibly
  address the challenges to the compensation. If
  effective, will allow a smaller crossing angle
  and more beam intensity.
• Provide direction to an IR upgrade path
• If compensation is proven to be effective,
  then the quadrupole-first option, possibly with
  flat beams, seems to be a more natural path for
  the IR upgrade. Otherwise, the dipole-first
  option will be more attractive.

44
Lessons from the SPS experiments
No wires activated

• Compensating 1 wire with another wire at nearly
  the same phase works
• Compensation is tune dependent
• Current sensitivity
• Alignment sensitivity
• Equivalent crossings in the same plane led to
  better lifetimes than alternating planes
• Beam lifetime t d3
• d is the beam-wire distance
• Higher power law expected given the
  proximity of high order resonances

Nearly perfect compensation
Both wires on
1 wire on
45
2nd prototype BBLR in the CERN SPS has
demonstrated benefit of compensation
G. Burtin, J. Camas, J.-P. Koutchouk, F.
Zimmermann et al.
46
Lessons from RHIC experiment

• Study at injection energy with 1 bunch and 1
  parasitic interaction per beam
• There is an effect to compensate, even with
  1 parasitic
• Drop in lifetime seen for beam separations lt 7 s
• Effect is very tune dependent
• How important are machine nonlinearities and
  other time dependent effects?
• Did they change with the beam-beam separation?

47
Wire compensation at RHIC

• Compensation of 1 wire by another wire worked
  well in the SPS under LHC conditions.
• Real test of the compensation principle requires
  2 beams
• Beam studies in RHIC show that parasitic
  interactions have strong influence on beam loss
• Favorable location for wire has been found in
  IR6, phase advance to parasitic 6 degrees at top
  energy

Proposed wire location
Location of parasitic
48
Milestones for future LHC Upgrade machine studies

• 2006 installation and test of a beam-beam long
  range compensation system at RHIC to be validated
  with colliding beams
• 2006/2007 new SPS experiment for crystal
  collimation, complementary to Tevatron results
• 2006 installation and test of Crab cavities at
  KEKB to validate higher beam-beam limit and
  luminosity with large crossing angles
• 2007 if KEKB test successful, test of Crab
  cavities in a hadron machine (RHIC?) to validate
  low RF noise and emittance preservation
• 2007-2009 LHC running-in and first machine
  studies on collimation and beam-beam

49
Tentative conclusions for the LHC IR Upgrade

• We do need a back-up or intermediate IR upgrade
  option based on NbTi magnet technology. What is
  the maximum luminosity?
• A vigorous RD programme on Nb3Sn magnets should
  start at CERN asap, in parallel to the US-LARP
  programme, to be ready for 1035 luminosity in
  2015
• Alternative IR layouts (quadrupole-first,
  dipole-first, D0, flat beams, Crab cavities) will
  be rated in terms of technological and
  operational risks/advantages

50
Towards a baseline design
Following the approach proposed by Barry Barish
for the ILC, we propose to

• Define a Baseline, i.e. a forward looking
  configuration which we are reasonably confident
  can achieve the required LHC luminosity
  performance and can be used to give an accurate
  cost estimate by mid-end 2006 in a Reference
  Design Report
• Identify Alternative Configurations and rate them
  in terms of technological and operational
  risks/advantages
• Identify RD (at CERN and elsewhere)
• To support the baseline
• To develop the alternatives

51
Reference LHC Luminosity Upgrade workpackages
and tentative milestones
52
LHC upgrade scenariosSummary

• The upgrade scenario currently assumed as
  baseline includes a reduction of b to 0.25 m, an
  increased crossing angle and a new
  bunch-shortening RF system.
• The corresponding peak luminosity with ultimate
  beam intensity is 4.6x1034 cm-2 s-1 at two IPs.
  Electron cloud effects and/or cryogenic heat
  loads may exclude the possibility to double the
  number of bunches.
• Milestones for future LHC Upgrade machine studies
  include RHIC tests on Long Range Beam-Beam
  compensation and possibly on crab cavity
  operation, after KEKB tests, SPS and Tevatron
  studies on crystal assisted collimation, as well
  as collimation, electron cloud, and beam-beam
  studies at the LHC itself.
• Several LHC IR upgrade options are currently
  being explored we need to converge to a baseline
  configuration and identify a few alternative
  options.

53
Additional Slides
54
Alternative ways to avoid luminosity loss

• Reduce crossing angle and apply wire
  compensation of long range beam-beam effects
• Crab cavities ? large crossing angles to avoid
  long range bb effects w/o luminosity loss.
  Potential of boosting the beam-beam tune shift
  (factor 2-3 predicted for KEKB, what about LHC?)
• Early beam separation by a D0 dipole located a
  few metres away from the IP, as recently
  suggested by JPK at the LHC-LUMI-05 workshop. The
  same effect could be obtained by tilted
  experimental solenoids, but the experiments dont
  seem to like the idea.
• A potential drawback of 2) and 3) is that DQbb is
  no longer
• reduced by the geometric factor F ? lower
  beam-beam limit?

55
Back to the Xing angle issue
An easy way to reduce or cancel the Xing angle
at the IP and gain 20 to 50 in luminosity. Is
it possible for the detectors?

Orbit corrector
Q1
Q3
Q2
J.-P. Koutchouk, LHC-LUMI-05
56
New idea D0 magnet a few meters away from the IP

• Advantages
• Cheap and elegant solution to increase luminosity
• No need of a new bunch shortening RF system
• Cleans collision debris from Q1?
• Possible drawbacks
• Reduced separation at first few parasitic
  encounters?
• Collision debris and background in the
  experiments?
• Compatibility with detector layout and
  integration into the experiments

57
LR beam-beam compensation remarks and open issues

• Simulations of LR compensation with 2 wires
  indicate that lifetime is recovered over a wide
  tune range but not for all tunes.
• The measured SPS lifetime is 5 ms x (d/s)5.
  Extrapolation to LHC beam-beam distance (9.5 s)
  would predict 6 minutes beam lifetime! Tevatron
  observations with electron lens show cubic
  dependence. Further SPS tests at different energy
  are needed.
• Lifetimes predicted by simulation codes are much
  larger than those observed, even though
  sensitivity to parameters seems correct. Needs
  further understanding and beam tests, e.g. at
  RHIC.
• For extreme PACMAN bunches there is
  overcompensation which causes the footprint to
  flip over or to increase instead of shrinking. To
  avoid degraded lifetime for PACMAN bunches, the
  wire should be pulsed train by train. It is
  rather challenging to make a pulsed wire for BB
  compensation the required average pulse rate is
  439 kHz and the turn-by-turn amplitude stability
  10-4.
• Experiments at RHIC (Fischer) with a single LR
  encounter show that the BB effect is visible
  starting from a 5s separation, consistent with
  Tevatron and Daphne observations, but contrary to
  LHC simulations and possibly earlier observations
  at the SPS collider.

58
RHIC experiment

• Studied at injection energy with 1 bunch and 1
  parasitic interaction per beam
• There is an effect to compensate, even with 1
  parasitic
• Drop in lifetime seen for beam separations lt 7 s
• Effect is very tune dependent

SPS t ? (d/s)5 Tevatron t d3 RHIC
t d4 or d2 measured 04/28/05, scan 4
59
LHC-LUMI-05 workshop some conclusions on the IR
Upgrade

• Local correction à la Raimondi, via dispersion
  inside triplet magnets and two pairs of
  sextupoles, can correct chromaticity and
  geometric aberrations ? look for a solution that
  can be implemented and removed anytime by varying
  quads and sexupole strengths
• Three IR layout options were identified that
  should be studied in more detail
• 1) dipole-first based on Nb3Sn technology with
  l 19 m
• 2) quad-first layout based on Nb3Sn technology l
  19 m
• 3) low gradient quad-first layout based on NbTi
  technology
• Still need to fix l and required length for TAS
  upgrade. Agreement to assume l 19 m as a
  reasonable estimate
• CARE-HHH web repository with optics solutions is
  very desirable ? we should all use the same input
  (MADX)
• Update the 3 proposals by the end of 2005

60
Energy Deposition Issues in LHC IR Upgrades, N.
Mokhov (FNAL)

• All three aspects, i.e. i) quench limit, ii)
  radiation damage (magnet lifetime), and iii)
  dynamic heat load on the cryo system should be
  simultaneously addressed in the IR magnet design.
  i) and ii) are linked
• Peak power deposition at non-IP end of IR magnets
  proportional to ?Bdl ? FDFD quadruplet
  focusing?
• Estimated dipole field with TAS in quad-first
  option to reduce peak energy deposition well
  below quench limits
• ? 15-20 Tm for magnetic TAS
• Estimated thickness of internal absorbers ? a 5
  mm thick SS absorber reduces peak power by a
  factor 2
• Impact of orbit corrector D0 inside the
  experiment on energy deposition in downstream
  magnets, including detector solenoid field
• ? more work needed, modest impact of
  solenoid
• field on energy deposition (more from
  fringe fields)

61
Action items/comments on energy deposition,
Nikolai Mokhov

• Refine and test scaling law for energy deposition
  in IR magnets with MARS simulations (including
  dependence on l)
• Introduce quench limits to JPKs spreadsheet for
  NbTi and Nb3Sn
• Address radiation damage/lifetime issues in all
  IR magnet design analyses 7 years at 1034 become
  8 months at 1035 with currently used materials ?
  new (ceramic type) materials for 1035?
• Launch RD program on beam tests for SC and
  insulating materials asap BNL, FNAL, MSU
• Arrive at a clear picture on Dynamic Heat Load
  limits. How serious is the current 10 W/m limit
  or 120 W on each side of IR? This becomes 100 W/m
  and 1.2 kW for 1035. Cooling scheme? Cryoplant
  capability?

62
Potential impact of novel magnet technology for
IR elements, Peter McIntyre

• Designs have been suggested for novel magnet
  technology to mitigate limitations from heat
  deposition and radiation damage from deposition
  of secondary particles in the quadrupole triplet
  and separation dipole. One example is an
  ironless quadrupole using structured-cable Nb3Sn
  conductor, which could provide 390 T/m gradient
  at a location as close as 12 m from the IP, and
  compatibility with supercritical helium flowing
  throughout the coils. A second example is a 9 T
  levitated-pole dipole for D1, which would open
  the transverse geometry so that secondaries are
  swept into a room-temperature flux return.
• In order to evaluate the potential benefit of
  these concepts it is necessary to model the heat
  deposition and radiation damage in the more
  compact geometries, and to examine potential
  interference with the performance of the
  detectors.
• Of particular importance is to undertake a
  consistent examination of the impact of reducing
  l on the ensemble of issues that impact
  achievable ? the interface of the IR with the
  machine lattice (chromaticity and dispersion,
  multipole errors, orbit errors, etc.), and the
  strategy for accommodating long-range beam-beam
  effects.
• Also of interest is to evaluate the pros and cons
  of the alternatives for operating temperature
  (superfluid, two-phase, or supercritical cooling)
  for the IR elements that must operate with
  substantial heat loads.

63
Latest design 9 Tesla _at_ 4.5 K
All windings are racetracks. Only pole tip
winding is Nb3Sn. All others are NbTi.
Support each pole piece using tension struts (low
heat load). 56 mm clear aperture
64

• Dipole-First optics (R. De Maria)
• matched optics solution for dipole-first layout
  for Beam1 and Beam2 with squeeze and tunability
  study
• 18 km b-max requires additional Q correction
• dispersion of 15 cm from D1/D2 arrangement for
  free
• could be increased for D ? 0 at the IP
• dispersion changes sign left and right from IP
• S. Fartoukh proposed a kissing scheme could
  allow equal signs of D but vertical D is quite
  small
• optics study relies on Nb3Sn technology
• ? 10 m long dipole magnets with B 15 T
• ? quadrupole magnets with 260 T/m and 80 mm
• aperture ? 11 T coil field
• ? IR layout provides magnetic TAS for free

65

• Alternative Dipole-First optics (O.Brüning)
• proposal of a low-gradient solution that
  could be realized with NbTi technology
• 18 km b-max requires additional Q correction
• maximum gradient of 70 T/m allows more than
• 200 mm diameter with a peak coil field of
  5.5 T
• Dispersion inside the triplet could be increased
  for
• D ? 0 at the IP
• Layout still requires an improved TAS absorber

66
CERN the Worlds Most Complete Accelerator
Complex (not to scale)
67
Injector chain for 1 TeV proton beams

• injecting at 1 TeV into the LHC reduces dynamic
  effects of persistent currents, i.e.
• persistent current decay during the injection
  flat bottom
• snap-back at the beginning of the acceleration ?
  easier beam control
• ? decreases turn-around time and hence
  increases integrated luminosity

with ?gas 85 h and ?xIBS 106 h (nom) ? 40 h
(high-L)
L0 cm-2s-1 tL h Tturnaround h Trun h ?200 days L dt fb-1 gain
1034 15 10 14.6 66 x1.0
1034 15 5 10.8 85 x1.3
1035 6.1 10 8.5 434 x6.6
1035 6.1 5 6.5 608 x9.2
68
Injector chain for 1 TeV proton beams
injecting in LHC more intense proton beams
with constant brightness, within the same
physical aperture ? will increase the peak
luminosity proportionally to the proton intensity

• at the beam-beam limit, peak luminosity L is
  proportional to normalized emittance ?n ??,
  unless limited by the triplet aperture
• an increased injection energy (Super-SPS) allows
  a larger normalized emittance ?n in the same
  physical aperture, thus more intensity and more
  luminosity at the beam-beam limit.
• the transverse beam size at 7 TeV would be larger
  and the relative beam-beam separation
  correspondingly lower long range beam-beam
  effects have to be compensated.

69
LHC injector complex upgrade

• CERN is preparing a road map for an upgrade of
  its accelerator complex to optimize the overall
  proton availability in view of the LHC luminosity
  upgrade and of all other physics users
• Scenarios under consideration include a new
  proton linac (Linac 4, 160 MeV) to overcome space
  charge limitations at injection in the PS Booster
  and a new Superconducting PS reaching an energy
  of 50-60 GeV
• This would open the possibility of a more
  reliable production of higher-brightness beams
  for the LHC, with lower transmission losses in
  the SPS thanks to the increased injection energy
• It would also offer the opportunity to develop
  new fast pulsing SC magnets in view of a
  Super-SPS, injecting at 1 TeV into the LHC