MARS15 energy deposition studies for LARP quadrupoles

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MARS15 energy deposition studies for LARP
quadrupoles

• April 27, 2006
• Igor Rakhno
• Fermi National Accelerator Laboratory

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• Model updates and restrictions
• Magnetic field scaling
• emax for quads with StSt liner and Ø 90, 100, 110
  mm
• emax vs liner thickness
• Alternative material for liner is W-25 Re
• Comparison between StSt and W-25 Re liners
• Spacers
• Dynamic heat load

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MARS15 code and IP5 model upgrade(from N. Mokhov)

• The MARS15 model of the IP5 inner triplet was
  substantially upgraded.
• LHC lattice v6.5.
• Recent changes in the CMS detector inner region
  and in the machine-detector interface have also
  been implemented into the model.
• MARS15 physics and transport models have been
  further improved.

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• Starting point for the updates
• Second generation high gradient quadrupoles for
  the LHC interaction regions
• T. Sen, J. Strait, and A. V.
  Zlobin - PAC 2001
• Beam physics issues for a possible 2nd
  generation LHC IR
• T. Sen, V. Kashikhin, P. Limon, N. Mokhov, I.
  Rakhno, J. Strait,
• M. Syphers, M. Xiao, A. Zlobin EPAC 2002
• Protecting LHC IP1/IP5 components against
  radiation resulting from
• colliding beam interactions
• N. Mokhov, I. Rakhno, J. Kerby, J. Strait
• LHC Project Report 633, 2003

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Key points to the model update

• All the thicknesses ?R for all the components,
  except for the liner, are kept constant.
• Radial distances are varied.
• Baseline liner thickness cold bore
• in Q1 6.21.5 mm
• in Q2A, Q2B, Q3 1.5 mm.

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Aperture restrictions from T.Sen, J.Strait,
A.Zlobin (PAC 2001)
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LHC IP5 LBQ
90-mm Nb3Sn quads
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LHC IP5 LBQ
90-mm Nb3Sn quads
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Cross section of a 90-mm Nb3Sn quad
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Normalization and spare space

• All results are normalized to the luminosity of
  1035 cm-2s-1.
• The design for the 90-mm Nb3Sn quads does not
  provide extra space for a liner in the region of
  Q2AB-Q3, just baseline.
• In the region of Q1 there are spare 3 mm.
• For the 100-mm Nb3Sn quads there are spare 5 mm
  for
• Q2AB-Q3 and 8 mm for Q1.

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Magnetic field scaling

• The magnetic field map from Vadim Kashikhin
• was used and the following scaling procedure was
• applied to keep the same gradient of 200 T/m
• (Bx, By)
• (X90, Y90) X90 ? X X90 (D(mm)/90)
• Y90 ? Y Y90
  (D(mm)/90)
• B90 ? B B90
  (D(mm)/90)

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Quench limit and the design goal(from N. Mokhov
and A. Zlobin)

• Current NbTi quads 1.6 mW/g and
  0.5 mW/g
• Nb3Sn quads for the upgrade 5.0 mW/g and 1.7
  mW/g

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Baseline StSt liner thickness
Design goal
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Baseline StSt liner thickness
Design goal
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Baseline StSt liner thickness
Design goal
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Peak power density vs inner coil diameter
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Peak power density vs extra liner thickness
Design goal
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Do we really need that thick liner?

• Energy deposition in the quads is mostly due to
  electromagnetic showers (e and ?).
• Electron and gamma spectra in the inner Q2B coil
• (in the hottest spot) reveal that about 50
  of all gammas
• are in the region of 200 - 400 keV.
• We can use high-Z material and take the advantage
  of increased photoabsorption at the same weight.

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Electron and gamma spectra in the hottest spot in
Q2B ?
e
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Photon interaction cross sections in iron and
tungsten
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• Tungsten Rhenium alloy (W-25 Re)
• 75 wt. W
• 25 wt. Re
• ? 19.7 g/cc
• www.matweb.com

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StSt liner vs W25 Re linerPeak energy deposition
in inner coil
Design goal
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Spacers

• Remove the SC cable from the hottest spots and
  fill in the empty space with a low-Z material -
  spacer.
• Two materials are considered aluminum and
  graphite.

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Spacers

• The spacers seems do not provide substantial
  local relief.
• A lot of computer time is required if this option
  is still of interest.

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Comparison between StSt and W-25 Re liners
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Comparison between StSt and W-25 Re
liners(TAS between Q1 and Q2A as well as liner
cooling at LN2 could help)
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Numerical data on dynamic heat load (W/m) in IP5
inner tripletwith the StSt and W-25 Re liners
of baseline thickness. Inner coil diameter 100
mm
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Conclusions

• Calculated data on emax and dynamic heat load for
  the LHC inner triplet with Nb3Sn quadrupoles of
  various diameters are provided.
• Several liner thicknesses are considered.
• StSt and W-25 Re liners are considered.
• StSt liner of increased thickness (baseline5mm)
  does not provide an adequate protection for the
  100-mm coils (emax gt1.7 mW/g).
• An alternative way to reduce emax in
  superconducting coils spacers (aluminum and
  graphite) does not look very promising.
• W-25 Re liner of increased thickness (baseline
  2 mm) provides an adequate protection for the
  100-mm coils (emax 1.2 mW/g) .

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Conclusions contd

• Dynamic heat loads scale with the luminosity,
  i.e. exceed
• 1 kW for the upgrade. Possible modifications
  of the quads
• can not give rise to a significant variation
  of the heat loads
• (it is true, at least, for the total heat
  load).
• The heat loads remain to be the outstanding issue
  putting constraints on the cooling system
  capability and the cryoplant capability and cost.
  This will be studied in great details in FY07,
  revisiting the idea of the inner absorber cooled
  at liquid nitrogen temperatures.
• Dipole-first scheme will be revisited in Q3 and
  Q4 of FY06.