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

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait2 LHC Luminosity Upgrade Why 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 to cm -2 s -1, will be very challenging.  Must consider several ways to achieve it.  Must start R&D now.  Must choose R&D directions judiciously.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait3 IR Upgrades – Opportunities and Challenges A new IR is one straightforward way to raise the LHC luminosity: Lower  *. 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...  max is in IR magnets. Energy deposition... 9 kW/beam from luminosity at cm -2 s -1. –Local peak power density => quench stability. –Total power into cryogenic system. –Radiation damage and activation.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait4 Baseline LHC IR Baseline LHC IR => “Quadrupoles First.” Quads as close as possible to IP => minimize  max. 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 

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait5 New IRs: “Straightforward” Designs Quads 1stDipoles 1st J. Strait, et al., Towards a New LHC Interaction Region Design for a Luminosity Upgrade, PAC Copy baseline IR with larger bore quads. Fewer long-range collisions, but larger  max.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait6 New IRs: Alternate Designs Twin Dipole 1stTwin Quads 1stQuads between Fewer long-range collisions, intermediate  max., complex twin-aperture quads and dipoles. Very large crossing angle layouts.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait7 Preliminary IR Design Studies Quad 1st Dipoles 1st Quad between Twin D 1st Twin Q 1st  cross (mrad)

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait8 Energy Deposition – Quads First Energy deposition and radiation are major issues for new IRs. In quad-first IR, E dep increases with L and decreases with quad aperture. –  max > 4 mW/g, (P/L) max > 120 W/m, P triplet >1.6 kW at L = cm -2 s -1. –Radiation lifetime for G11CR < 6 months at hottest spots. T. Sen, et al., Beam Physics Issues for a Possible 2 nd Generation LHC IR, EPAC 2002.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait9 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.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait10 Cryogenic System Challenges A.V. Zlobin, et al., Large-Aperture Nb3Sn Quadrupoles for 2 nd Generation LHC IRs, EPAC Many large cooling channels required to remove heat, even with super- fluid He.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait11 Energy Deposition – Dipoles First Problem is even more severe for dipole-first IR. –  max on mid-plane ~ 50 mW/g; P dipole ~3.5 kW for L = 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.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait12 TAS Most charged particles entering dipole are swept into the magnet. TAN

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait13 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.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait14 IR Upgrade Questions and Issues IR design concepts shown reduce  * by x2 – x5 w.r.t. baseline design. But… Larger  crossing 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  xy.) –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….)

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait15 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  -functions?

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait16 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 B op 8 T -> 13~15 T in dipoles or at pole of quad => Nb 3 Sn. All designs put a premium on large apertures: –Increasing  max decreases  * => 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. Nb 3 Sn is favored for maximum field and temperature margin, but considerable R&D is required to master this technology.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait17 NbTi Magnets for IR Upgrades? Quad-first IR with Nb 3 Sn quads of 110 mm aperture and 6m length can achieve  * = 16 cm. To achieve same  * with NbTi (=> lower pole-tip field) requires aperture of 120~130 mm and length of 8~9 m. =>~30% increase in  max ; 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 Nb 3 Sn. 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.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait18 Summary “Simple” IR upgrades – quad-first or dipoles-first – using Nb 3 Sn have the potential to reduce  * by x2~x3. “Exotic” IR upgrades – “quads between” and large crossing angle layouts – might reduce  * by x2.5~x5. Energy deposition and radiation hardness are major challenges for L = cm -2 s -1, especially for the dipole-first case. Nb 3 Sn technology offers greater upgrade potential than NbTi, but considerable R&D is required. The challenge of increasing LHC luminosity towards cm -2 s -1 is considerable, and many options need to be pursued now to ensure success.