R. Ostojic CERN, AT Department

1. General Considerations for the Upgrade of the LHC Insertion Magnets R. Ostojic CERN, AT Department

2. LHC Insertion Magnets Final focus Matching section Separation dipoles Dispersion suppressor 154 superconducting magnets: • 102 quadrupoles cooled at 1.9 K, with gradients of 200 T/m • 52 dipoles and quadrupoles cooled at 4.5 K, with fields of 4 T and gradients of 160 T/m

3. LHC Magnet Classes • MB – class (MB, MQ, MQM) (8.5 T, Nb-Ti cable at 1.9 K; m-channel polyimide insulation) 1b. MQX- class (MQXA, MQXB) (8.5 T; Nb-Ti cable at 1.9 K; closed-channel polyimide insulation) 2.MQY- class (MQM, MQY) (5 T; Nb-Ti cable at 4.5 K; m-channel polyimide insulation) 3. RHIC – class (D1, D2, D3, D4) (4 T; Nb-Ti cable at 4.5 K; closed-channel polyimide insulation) 4. MQTL – class (MQTL, MCBX and all correctors) (3 T; Nb-Ti wire at 4.5 K; impregnated coil) 5. Normal conducting magnets (MBW, MBWX, MQW) (1.4 T; normal conducting; impregnated coil)

4. Upgrade of the Matching Sections and Separation Dipoles • The present matching quadrupoles are state-of-the-art Nb-Ti quadrupoles which operate at 4.5 K. • The upgrade of the matching sections should in the first place focus on modifying the cooling scheme and operating the magnets at 1.9 K. • In case larger apertures are required, new magnets could be built as extensions of existing designs. • The 4 T-class separation dipoles should be replaced with higher field magnets cooled at 1.9 K. • The MQTL-class should be replaced by magnets more resistant to high radiation environment.

5. The LHC low-b triplet Q3 Q2 Q1 TASB DFBX MQXA MQXB MQXB MQXA 6.37 5.5 5.5 6.37 2.985 2.715 1.0 MCSOX a3 a4 b4 MCBXA MCBXH/V b3 b6 MQSX MCBX MCBXH/V MCBX MCBXH/V

6. LHC low-b triplets

7. Limits of the present LHC triplets • Aperture 70 mm coil 63 mm beam tube 60 mm beam screen b* = 0.55 m • Gradient • 215 T/m operational 205 T/m • Field quality • Excellent, no need for correctors down to b* ~ 0.6 m • Peak power density • 12 mW/cm3 L = 3 1034 • Total cooling power • 420 W at 1.9 K L = 3 1034

8. Aperture issue • The coil aperture was the most revisited magnet parameter of the low-b quadrupoles. • Aperture of 70 mm defined in the “Yellow Book” (1995, nominal b*= 0.50 m, ultimate 0.25 m). • Subsequent studies showed a need for increasing the crossing angle by a factor of two. • e-cloud instability  introduction of beam screens. • Upgrade target remains a b* of 0.25 m (irrespective of magnet technology). • Luminosity increase by a factor ~1.5. • Higher luminosity implies substantially greater load on the cryogenic system. • feedback to the choice of aperture and magnet design.

9. Enabling operation of the LHCwith minimal disruption • Maintenance and repair of insertion magnets: • Large number of magnets of different type means limited number of spare magnets ready for exchange. • A facility is planned at CERN for repair/rebuild of matching section quadrupoles. • Particular problem: low-beta quadrupoles and separation dipoles • Only one spare of each type (best magnets already in the LHC). • As of 2006, there will be no operating facility for repair and testing of these magnets.

10. Quadrupole-first layouts Optimize the aperture and length of the quadrupoles according to their position in the triplet. Use of aperture: • Increase the aperture to reduce heat loads (peak and total) • Profit from better field quality to reduce the number of correctors and introduce stronger orbit correctors • Decrease b* to complement other ways of increasing luminosity.

11. Large aperture quadrupoles using existing LHC cables

12. Large aperture quadrupoles Operating current at 80% of conductor limit As the quadrupole aperture increases, the operating gradient decreases by 20 T/m for every 10mm of coil aperture. To get a GL similar to the present triplet, quadrupole lengths need to be increased by 20-30%. The Nb-Ti technology proven for quadrupoles up to 12 m long.

13. LHC dipoles FRESCA, 10 T, 88 mm D. Leroy et al., 1999 C. Meuris et al, 1999 R&D directions for Nb-Ti quads • Technology and manufacturing issues are well mastered. • Relatively easy extension of main magnet parameters (aperture and length) without extensive R&D. • Focus R&D on magnet “transparency”: • Cable and coil insulation • Thermal design of the collaring and yoking structures • Coupling to the heat exchanger

14. Summary • LHC contains several generations of Nb-Ti magnets. Extensive experience exists in building magnets of different aperture and length. Upgrading the magnets to a higher class should be considered as a first option. • Nb-Ti (1.9K) technology is a clear choice for upgrading the large number of magnets in the LHC insertions (dipoles and quadrupoles) of the 4 T class. • The availability of spare low-b triplets and separation dipoles is a serious concern. Any proposal for the upgrade must take this issue into account and provide an appropriate solution. • The shortest route for providing new magnets in a time frame compatible with LHC luminosity runs is to use Nb-Ti technology. • Nb-Ti (1.9K) technology has reached its limits for large series production with the LHC main dipoles; improvements for small series are still possible.

15. Comment • It is generally accepted that a new generation of magnets (Nb3Sn, HTS,…) will be required for the next hadron collider. CERN should take part in a wider effort to develop and demonstrate the feasibility of the new technology. • In the interest of LHC operation, we must have an alternative; Nb-Ti technology can offer an appropriate intermediate solution. • The pitfalls in building Nb-Ti magnets should not be underestimated. There is a need to start design studies and development before LHC construction teams move on to other projects. • Initial experience from operating the LHC with beam is crucial for refining magnet parameters and making sure there are no “unknown unknowns”.