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Overview of Possible LHC IR Upgrade Layouts

US LHC Accelerator Research Program. bnl - fnal - lbnl - slac. Overview of Possible LHC IR Upgrade Layouts. CARE HHH-2004 Workshop CERN 8-11 November 2004 J. Strait, N.V. Mokhov, T. Sen Fermilab. LHC Luminosity Upgrade Why and When?.

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Overview of Possible LHC IR Upgrade Layouts

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  1. US LHC Accelerator Research Program bnl - fnal - lbnl - slac Overview of Possible LHC IR Upgrade Layouts CARE HHH-2004 WorkshopCERN8-11 November 2004 J. Strait, N.V. Mokhov, T. SenFermilab

  2. LHC Luminosity UpgradeWhy and When? A luminosity upgrade of the LHC will be required by the middle of the next decade to keep the LHC physics program productive. To raise the the LHC luminosity by x10, from 1034 to 1035 cm-2s-1, will be very challenging. • Must consider several ways to achieve it. • Must start R&D now. • Must choose R&D directions judiciously. IR Upgrades Layouts - J. Strait

  3. IR Upgrades – Opportunities and Challenges • A new IR is one straightforward way to raise the LHC luminosity: • Lower b*. • Reduce effect of parasitic collisions. • IR upgrade alone cannot achieve x10 increase in L. • At most x2~x3 seems possible from IR upgrade alone. • But IR must deal with higher beam current and with x10 increase in power from collision debris. • Principle technical challenges of IR design: • Field quality and alignment . . . bmax is in IR magnets. • Energy deposition . . . 9 kW/beam from luminosity at 1035 cm-2s-1. • Local peak power density => quench stability. • Total power into cryogenic system. • Radiation damage and activation. IR Upgrades Layouts - J. Strait

  4. Baseline LHC IR • Baseline LHC IR => “Quadrupoles First.” • Quads as close as possible to IP => minimize bmax. • Quads are “inefficient” at sweeping charged particles: => “modest” peak power deposition. • But, beams share common channel:=> many parasitic collisions.=> correction system acts on both beam simultaneously. IP_ IR Upgrades Layouts - J. Strait

  5. New IRs:“Straightforward” Designs Quads 1st Dipoles 1st Copy baseline IR with larger bore quads. Fewer long-range collisions, but larger bmax. J. Strait, et al., Towards a New LHC Interaction Region Design for a Luminosity Upgrade, PAC 2003. IR Upgrades Layouts - J. Strait

  6. Quads between Twin Quads 1st Twin Dipole 1st New IRs:Alternate Designs Fewer long-range collisions, intermediate bmax.,complex twin-aperture quads and dipoles. Very large crossing angle layouts. IR Upgrades Layouts - J. Strait

  7. Quad 1st Dipoles 1st Quad between Twin D 1st Twin Q 1st Preliminary IR Design Studies qcross (mrad) 0.30 0.53 0.42 0.49 7.5 7.8 IR Upgrades Layouts - J. Strait

  8. Energy Deposition – Quads First • Energy deposition and radiation are major issues for new IRs. • In quad-first IR, Edep increases with L and decreases with quad aperture. • emax> 4 mW/g, (P/L)max> 120 W/m, Ptriplet>1.6 kW atL = 1035 cm-2 s -1. • Radiation lifetime for G11CR < 6 months at hottest spots. T. Sen, et al., Beam Physics Issues for a Possible 2nd Generation LHC IR, EPAC 2002. IR Upgrades Layouts - J. Strait

  9. Absorbers to Protect Triplet Quadrupoles Front absorber (TAS) to limit flux hitting quads. Internal absorbers to spread showers => limit peak power density. T. Sen, et al., Second Generation High Gradient Quadrupoles for the LHC IRs, PAC 2001. IR Upgrades Layouts - J. Strait

  10. Cryogenic System Challenges Many large cooling channels required to remove heat, even with super-fluid He. A.V. Zlobin, et al., Large-Aperture Nb3Sn Quadrupoles for 2nd Generation LHC IRs, EPAC 2002. IR Upgrades Layouts - J. Strait

  11. Energy Deposition – Dipoles First • Problem is even more severe for dipole-first IR. • emax on mid-plane ~ 50 mW/g; Pdipole ~3.5 kW for L = 1035 cm-2 s -1. • “Exotic” magnet designs required, whose feasibility is not known. N.V. Mokhov, et al., Energy Dep.Limits in a Separation Dipole in Front of the LHC High-L Inner Triplet, PAC 2003. IR Upgrades Layouts - J. Strait

  12. TAN Most charged particles entering dipole are swept into the magnet. TAS IR Upgrades Layouts - J. Strait

  13. Open Mid-Plane Dipole • Open mid-plane => showers originate outside the coils; peak power density in coils is reasonable. • Tungsten rods at LN temperature absorb significant radiation. • But, can this magnet be made to work?? R. Gupta and N.V. Mokhov, LARP Collaboration Meeting, Napa, CA, Oct 2004. IR Upgrades Layouts - J. Strait

  14. IR Upgrade Questions and Issues • IR design concepts shown reduce b* by x2 – x5 w.r.t. baseline design. • But… • Larger fcrossing and larger beam divergence limit the increase in L. • Shorten bunches with more RF? (Expensive even for x2 reduction.) • Crab crossing? (Difficult to provide enough crab cavity voltage. Any imperfections in crab system will blow up exy .) • Increase bunch current? (Other factors may limit beam current below what it needed.) • Factors limiting luminosity won’t be fully understood without LHC running experience. • Other developments may influence design choice. (e.g. active beam-beam compensation; requirements by the experiments….) IR Upgrades Layouts - J. Strait

  15. Other Beam Physics Questions • Are the (very) large crossing angle schemes (twin-aperture dipole or quad first) in any way feasible? • Can dispersion suppressors be designed for the non-parallel axis quadrupole cases? • Can triplet errors be adequately corrected given the very large b-functions? IR Upgrades Layouts - J. Strait

  16. Magnet R&D Challenges • All designs put a premium on achieving very high field: • Maximizes quadrupole aperture for a given gradient. • Separates the beams quickly in the dipole first IR => bring quads as close as possible to the IP. • Push Bop 8 T -> 13~15 T in dipoles or at pole of quad => Nb3Sn. • All designs put a premium on large apertures: • Increasing bmax decreases b* => quad aperture up to 110 mm? • Large beam offset at non-IP end of first dipole.=> Dipole horizontal aperture >130 mm. • Energy deposition: quench stability, cooling, radiation hard materials. • Nb3Sn is favored for maximum field and temperature margin, but considerable R&D is required to master this technology. IR Upgrades Layouts - J. Strait

  17. NbTi Magnets for IR Upgrades? • Quad-first IR with Nb3Sn quads of 110 mm aperture and 6m length can achieve b* = 16 cm. • To achieve same b* with NbTi (=> lower pole-tip field) requires aperture of 120~130 mm and length of 8~9 m. • => ~30% increase in bmax; 15~20% more parasitic collisions. • But • Current NbTi technology is not sufficiently radiation hard. • Smaller temperature margin => more sensitive to beam heating. • And dipole-first IR requires highest possible field: • Separate beams quickly. • Bring quads as close as possible to the IP. • => Probably not practical without higher performance of Nb3Sn. See also F.Ruggiero, et al., Performance Limits and IR Design of a Possible LHC Luminosity Upgrade Based on NbTi SC Magnet Technology, EPAC 2004. IR Upgrades Layouts - J. Strait

  18. Summary • “Simple” IR upgrades – quad-first or dipoles-first – using Nb3Sn have the potential to reduce b* by x2~x3. • “Exotic” IR upgrades – “quads between” and large crossing angle layouts – might reduce b* by x2.5~x5. • Energy deposition and radiation hardness are major challenges for L = 1035 cm-2 s -1, especially for the dipole-first case. • Nb3Sn technology offers greater upgrade potential than NbTi, but considerable R&D is required. • The challenge of increasing LHC luminosity towards 1035 cm-2 s -1 is considerable, and many options need to be pursued now to ensure success. IR Upgrades Layouts - J. Strait

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