J-P Koutchouk , CERN

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Possible Quadrupole-first Options with beta lt
0.25 m

• J-P Koutchouk , CERN

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Outline

• Requirements and objectives
• Overview of the anticipated advantages and
  drawbacks of the quad-first solution
• Hints from the LHC design
• The yield from a reduced beta
• The internal wheels of the simplified scaling
  model used
• Comparison of a range of solutions
• Conclusions of this exercise

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Some sources

• F. Ruggiero et al., Possible scenarios for an LHC
  upgrade, HHH2004, CERN-2005-006.
• J. Strait et al., Overview of possible LHC IR
  Upgrade Layouts, HHH2004, CERN-2005-006.
• several other contributions in the same
  workshop
• F. Ruggiero et al., Performance limits and IR
  design for an LHC upgrade, EPAC2004.
• R. Ostojic et al., Low-beta quad designs for the
  LHC upgrade, PAC2005
• J. Strait, Very high gradient quads, PAC2001.
• P. McIntyre et al., Towards an optimization of
  the LHC IR using new Magnet technology, PAC2005.
• T. Sen et al., Beam physics issues for the IR
  upgrade.
• T. Sen et al. PAC2001.

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Requirements and objectives

• The IR upgrade design cannot be split in slices,
  as before. All requirements must be incorporated
  from the start and the technology is leading the
  dance. ?Need for a global model
• A clear view of the performance objective
• Make up for a beam current that does not reach
  nominal value
• Contribute in a significant way to the factor 10
  in lumi increase.
• The ideal being a lego system that allows both.
• Be ready for installation in 2012/2015
• Robust design to cope for unknowns if a new
  technology is to be used.
• Maximize the probability for an efficient
  take-off
• Depending on the objective, the behavior versus
  the energy deposition and radiation lifetime are
  obviously major issues.

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General Advantages and Drawbacks
Advantages Drawbacks
Minimization of ßmax, optical aberrations and sensitivity most robust optics solution. Larger potential for beta reduction Strong coupling to other upgrade options thru Xing angle and aperture goal must be well defined
The magnet most exposed to debris is as well the less sensitive (sweeps less) A priori, long-range beam-beam stronger
Builds on the operational experience of 1rst generation potential gain in ??dt The two LHC rings remain coupled operations more involved but large experience

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Hints from the LHC Design

• The arc sextupoles are specified for the
  chromatic correction (first and second order) of
  4 low-beta insertions (l23/21 m) tuned at 25 cm
  (LHC PN38) for a 90 degree phase advance (version
  4).
• The 2nd order Chrom. can as well be minimized by
  adjusting the betatron phase shift between IPs
  (LHC PN103)
• The structure of the LHC optics allows reducing
  ß to 25 cm.
• An optics solution must include a well behaved
  un-squeeze to the injection optics can be
  difficult and time-consuming. The difficulty
  increases rapidly with ?.

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The yield from a reduced beta

• Luminosity increase vs beta
• no Xing angle,
• nominal Xing and bunch length,
• BBLR?,
• Bunch length/2

For both options and even more for the Q first,
pushing the low-beta makes sense if
simultaneously the impact of the Lumi.
geometrical factor is acted upon.
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A simple-minded exploration of the triplet
parameter space

• Goal Investigate solutions based on a scaled LHC
  triplet vs
• distance to the IP,
• ß
• Beam intensity
• Xing strategy and beam-beam compensation
• Quadrupole length
• Quadrupole technology
• oversize factor for the inner coil diameter
• Model output

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Discussion of the options (1)

• Ingredients, scaling laws and recipes
• Xing strategy small angle HV, HH, HHBBLR
• Triplet layout same as LHC with same relative
  quad. lengths. LHC inter-quad space kept
  unscaled.
• Gradient All triplet quads have the same
  gradient scaled from nominal by
  
• followed by matching consisting in getting
  reasonable ßs and as at Q4 by small trims the
  gradient.
• ltlQgt average quad length.

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Discussion of the options (2)

• Ingredients, scaling laws and recipes
• Maximum beam extent ßmax, s, a_disp, beam sep.
  are all taken in the middle of Q2 (thick lens
  transport), nominal e.
• Beam extent due to dispersion usual momentum
  range (0.86 E-3) in presence of spurious
  dispersion (0.4m in the arcs) and the vertical
  dispersion excited by the HV Xing scheme.
• ?LR Long-range interaction length ?IP
  ?triplet2

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Discussion of the options (3)

• Ingredients, scaling laws and recipes
• Xing angle BBLR suppresses intensity dependence
• Beam separation effect of the Xing angle
  transported to the mid-Q2 gives about 9.5 sigma.
• Beam aperture

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Discussion of the options (4)

• Ingredients, scaling laws and recipes
• K2 Relative excitation of the lattice sextupoles
  scaled from version 4 (LHCPN38) 20 inefficiency
  due to phase advance.
• Geometric aberrations

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Discussion of the options (5)

• Ingredients, scaling laws and recipes
• Innercoil diameter
• Margins and efficiencies
• For NbTi and NbTiTa, ultimate performance is
  taken at 66 of critical field (13T, 14T), i.e.
  8.6T and 9.2T.
• For Nb3Sn, this is taken to 57 of 23T, i.e. 13T.
• The efficiency measures how this ultimate
  performance is approached. I understand a margin
  of 20 is usually wanted.

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Discussion of the options (6)

• Ingredients, scaling laws and recipes
• Power deposition in the coil
• First attempt, based on few readings
• Nominal taken to be 0.4 mW/g 5s chosen to fit a
  doubling of the
• power deposition as calculated by A. Mokhov.

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Case Studies (1)

• Strategy
• Scenario where the beam intensity cannot exceed
  nominal/2.
• Do nothing
• Squeeze to aperture
• Move the triplet towards the IP
• Complement each MQX with a MQY
• Upgrade based on NbTi technology
• Test some former proposals
• Optimize at l23m
• Investigate triplet closer to IP

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Case Studies (2)

• Strategy
• Upgrade based on Nb3Sn technology
• Investigate at l23m
• Investigate at l19m
• Investigate at l16m
• Investigate at l12m

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Nominal LHC
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Intensitynominal/2
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Intensitynominal/2 squeeze to aperture
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Intensitynominal/2 squeeze to aperture HH Xing
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Intensitynominal/2 triplet pushed by 4m towards
IP
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Intensitynominal/2 add a MQY to each MQX
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Intensitynominal/2 new NbTiTa insertion
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Partial conclusion on making up for a too small
beam intensity

• As is, the baseline triplet offers a very
  limited potential for compensating a beam current
  lower than anticipated (20 to 30 in ?).
• Pushing the triplet by 4m towards the IP yields
  an increase of 50 in ? . The peak field reaches
  7.5T but the power deposition is 2 times lower
  than nominal.
• To double the luminosity, NbTiTa is necessary but
  the solution appears stretched (need to start at
  19m from IP, small margin, high chromatic and
  geometric aberrations)

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Epac2004 solution
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Pac2005 Cern solution
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Very long and large weak quadrupoles
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Optimization at l23m
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Optimization at l23m
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Partial conclusion on an upgrade using NbTi or
NbTiTa technology

• According to the model, the EPAC2004 solution is
  too demanding. This is traced to the extra
  aperture required by a 9.5 s separation and the
  Dy due to the HV Xing.
• The Ostojic et al. solution (l23m) works if the
  coil diameter is enlarged to 110 or better 120 mm
  and the technology NbTiTa used. ? increases by
  40.
• Very long (16m) and large (212mm) weak (5.5T)
  quads appear to give a modest luminosity increase
  (25) and large geometric aberrations but have
  some advantages (losses).

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Partial conclusion on an upgrade using NbTi or
NbTiTa technology(2)

• The same ? increase is more easily obtained
  (diameter 105 mm) by pushing the triplet towards
  the IP (l18m). It seems the only possibility
  for the NbTi technology.

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Nb3Sn Optimization at l23m
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Nb3Sn Optimization at l23m, high intensity
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Nb3Sn Optimization at l23m, high intensity,
BBLR
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Partial conclusion on an upgrade using Nb3Sn
technology (1)

• A solution very similar to the baseline triplet
  exists with coil diameter of 95 mm, dipole length
  of 5.5 m with a 1.5 increase in ?.
• For the full upgrade (Ib2), the diameter and
  length required increase to 121mm and 6.7m. With
  BBLR/HH Xing, this increase is not needed and ?
  increases further.
• Luminosity and feasibility both increase when
  pushing the triplet towards the IP

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Partial conclusion on an upgrade using Nb3Sn
technology (2)
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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
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Nb3Sn Optimization at l19m, Xing/2 at IP
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Beyond triplets?

• The ideal solution would be a two-stage system
• Performance booster made of a doublet or triplet
  pushed inside the detector, optimized for its
  environment, i.e. with large margins,
  transparency, could accept some technological or
  planning risk
• Followed by a triplet/dipole or dipole/triplet
  with more conservative design, margins,that
  could provide a performance increase even in the
  absence of the booster (some resemblance with the
  LEP solution with a warm back-up of the sc
  low-beta doublet).
• Investigations to be done this fall.

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Conclusions (1)

• The baseline triplet or small variations around
  it offer a very modest potential for luminosity
  improvement.
• The NbTi(Ta) technology can offer an improvement
  in luminosity of the order of 40 but requires
  some 120 mm diameter at 23m from the IP. At 18m,
  this is reduced to 105 mm. This option does not
  seem compatible with an increase of the beam
  intensity.
• These limits are removed by the Nb3Sn technology.
  A significant improvement in the performance and
  feasibility is observed with BBLR and when moving
  the triplet toward the IP.

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Conclusions

• What about separating the beams as early as
  possible with an orbit corrector?
• Investigations are planned on a two-stage system
  with the goal of mitigating the technological
  challenges.

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