Nb 3 Sn IR Quadrupoles for HL-LHC

1. BNL - FNAL - LBNL - SLAC Nb3Sn IR Quadrupoles for HL-LHC GianLuca Sabbi for the US LHC Accelerator Research Program 2012 Applied Superconductivity Conference

2. High Luminosity LHC • Physics goals: • Improve measurements of new phenomena seen at the LHC • Detect/search low rate phenomena inaccessible at nominal LHC • Increase mass range for limits/discovery by up to 30% • Required accelerator upgrades include new IR magnets: • Directly increase luminosity through stronger focusing •  decrease b* • Provide design options for overall system optimization/integration •  collimation, optics, vacuum, cryogenics • Be compatible with high luminosity operation •  Radiation lifetime, thermal margins • Major detector upgrades are also required to take full advantage of SLHC

3. LARP Magnet Program Goal: Develop Nb3Sn quadrupoles for the LHC luminosity upgrade Potential to operate at higher field and larger temperature margin • R&D phases: • 2004-2010: technology development using the SQ and TQ models • 2006-2012: length scale-up to 4 meters using the LR and LQ models • 2008-2014: incorporation of accelerator quality features in HQ/LHQ • Program achievements to date: • TQ models (90 mm aperture, 1 m length) reached 240 T/m gradient • LQ models (90 mm aperture, 4 m length) reached 220 T/m gradient • HQ models (120 mm aperture, 1 m length) reached 184 T/m gradient • Current activities: • Completion of LQ program: test of LQS03 to reproduce TQS03 result • Optimization of HQ, fabrication of LHQ(technology demonstration) • Design and planning of the MQXF IR Quadrupole development

4. Nb3Sn Technology Challenges • Brittleness: • React coils after winding • Epoxy impregnation • Strain sensitivity: • Mechanical design and analysis to • prevent degradation under high stress Cable Critical Current (kA) Transverse Stress (MPa)

5. R&D Program Components SM  LR • Racetrack coils, shell based structure • Technology R&D in simple geometry • Length scale up from 0.3 m to 4 m TQS  LQS • Cos2q coils with 90 mm aperture • Incorporation of more complex layout • Length scale up from 1 m to 4 m HQ  LHQ • Cos2q coils with 120 mm aperture • Explore force/stress/energy limits • Nb3Sn Technology Demonstration

6. Overview of LARP Magnets TQS LQS SQ SM LR HQ TQC

7. Program Achievements - Timeline (1/3) • Mar. 2006 SQ02 reaches 97% of SSL at both 4.5K and 1.9K • Demonstrates MJR 54/61conductor performance for TQ • Jun. 2007 TQS02a surpasses 220 T/m at both 4.5K and 1.9K (*) • Achieved 200 T/m goal with RRP 54/61 conductor • Jan. 2008 LRS02 reaches 96% of SSL at 4.5K with RRP 54/61 • Coil & shell structure scale-up from 0.3 m to 4 m • July 2009 TQS03a achieves 240 T/m (1.9K) with RRP 108/127 (*) • Increased stability with smaller filament size • Dec. 2009 TQS03b operates at 200 MPa (average) coil stress (*) • Widens Nb3Sn design space (as required…) • (*) Tests performed at CERN

8. Program Achievements - Timeline (2/3) • Dec. 2009 LQS01a reaches 200 T/m at both 4.5K and 1.9K • LARP meets its “defining” milestone • Feb. 2010 TQS03d shows no degradation after 1000 cycles (*) • Comparable to operational lifetime in HL-LHC • July 2010 LQS01b achieves 220 T/m with RRP 54/61 • Same TQS02 level at 4.5K, but no degradation at 1.9K • Apr. 2011 HQ01d achieves 170 T/m in 120 mm aperture at 4.5 K • At HL-LHC operational level with good field quality • Oct. 2011 HQM02 achieves ~90% of SSL at both 4.6 K and 2.2 K • Special coil to test reduced compaction • (*) Test performed at CERN

9. Program Achievements - Timeline (3/3) • Apr. 2012 HQ01e-2 reaches 184 T/m at 1.9K (*) • Despite using first generation coils, several known issues • Above linear scaling from TQ (240/120*90=180 T/m) • Jun. 2012 HQM04 reaches 97% SSL at 4.6K and 94% at 2.2K • Successful demonstration of revised coil design • Single-pass cored cable, lower compaction • Next Steps: • Aug. 2012 LQS03 test: reproduce TQS03 using 108/127 conductor • Dec. 2012 HQ02a test: improve performance with 2nd generation coils • (*) Test performed at CERN

10. Summary – Technical Progress • Steady advances in addressing technology issues that were initially perceived as potential show stoppers: • Conductor performance/stability, mechanical support, degradation due to stress and cycling, length scale-up, coil and structure alignment, field quality, quench protection, heat extraction and radiation lifetime • Today, we can confidently say that there are no show stoppers • However, we are behind in addressing a number of accelerator quality and production relevant issues, which affect the overall system performance, and ultimately the feasibility and success of the project: • Control of dynamic effects, insulation of long lengths of cable, increased electrical integrity, process documentation and QA,incorporation of rad-hard epoxies, evaluation and selection among candidate conductors • Since last year we have significantly stepped up the pace in introducing these features. Results have been generally positive but we need to manage the risk associated with multiple/combined changes

11. Handling High Stress in Magnet Coils 1. Understand limits 2. Optimize structure and coil for minimum stress TQ (90 mm, ~12 T) LQ (90 mm, ~12 T) HQ (120 mm, ~15 T) Titanium pole Key location Coil geometry 170 MPa 180 MPa 4.5K, 0T/m SSL preload 4.5K, 0T/m SSL preload 4.5K, 0T/m SSL preload 170 MPa 190 MPa 200 MPa

12. Technology Quadrupole (TQ) • Double-layer, shell-type coil • 90 mm aperture, 1 m length • Two support structures: • - TQS (shell based) • - TQC (collar based) • Target gradient200 T/m TQC TQS Winding & curing (FNAL - all coils) Reaction & potting (LBNL - all coils)

13. TQ Studies: Stress Limits Coil layer 1 stress evolution - sq Calculated peak stresses in TQS03c 260 MPa @ 4.5K • Systematic investigation in TQS03: • TQS03a: 120 MPa at pole, 93% SSL • TQS03b: 160 MPa at pole, 91% SSL • TQS03c: 200 MPa at pole, 88% SSL • Peak stresses are considerably higher • Considerably widens design window 255 MPa @ SSL

14. TQS03d Cycling Test • Reduced coil stress to TQS03b levels (160 MPa average) • Pre-loading operation and test performed at CERN • Did not recover TQS03b quench current (permanent degradation) • Performed 1000 cycles with control quenches every ~150 cycles • No change in mechanical parameters or quench levels

15. High-Field Quadrupole (HQ) • 120 mm aperture, coil peak field of 15.1 T at 219 T/m (1.9K SSL) • 190 MPa coil stress at SSL (150 MPa if preloaded for 180 T/m) • Stress minimization is primary goal at all design steps (from x-section) • Coil and yoke designed for small geometric and saturation harmonics • Full alignment during coil fabrication, magnet assembly and powering

16. Mechanical Design Space in HQ models Pole quenches (HQ01d) Pole stress during ramp to quench (HQ01d) • Pole quenches and strain gauge data indicate insufficient pre-load • Mid-plane quenches indicate excessive pre-load • Narrow design and assembly window: ok for an R&D model designed to explore stress limits, may require optimization for production, in particular if the aperture is further increased Mid-plane Quenches (HQ01d)

17. Assembly Optimization in HQ01e • HQ explores stress limits and test results confirm pre-load window is very narrow • HQ01e: asymmetric loading for better stress uniformity P. Ferracin, H. Felice

18. Performance issues in early HQ Tests • Mechanical issues: • Ramp rate dependence of first three models is indicative of conductor damage • Electrical issues: • Large number of insulation failures in coils, in particular inter-layer and coil to parts HQ01a-d Ramp Rate dependence HQ01b extraction voltage Extraction Voltage (V) M. Martchevsky Time (s)

19. Initial Findings • Conductor damage was traced to excessive strain during the coil reaction phase: • No/insufficient gaps were included in pole segments to limit longitudinal strain • Assumed less space for inter-turn insulation than TQ/LQ  higher compaction • Electrical failures due to insufficient insulation and weaknesses at critical locations • Compounded by lack of electrical QA (Over) size measurements of completed coil Coil spring back in tooling H. Felice, G. Ambrosio, R. Bossert, R. Hafalia, J. Schmalzle

20. Progress with new coil series Coil 15 was tested in HQM04 mirror, reaching 97% of SSL at 4.5K, 94% at 2.2K D. Dietderich, A. Godeke, R. Bossert, G. Chlachidze • However, some issues are still appearing: • Low compaction in coil 17 after curing • Gaps did not close after reaction – may or may not be related • Many popped strands in coil 18 winding and (first in HQ) turn-to-turn short • Process control issues or variability due to recent changes?

21. Field Quality Studies in HQ01d-e • Good start on geometric harmonics, showing size uniformity and alignment • Persistent current effects are large but within limits set by design study • Large dynamic effects indicate need to better control inter-strand resistance Eddy current harmonics for different ramp rates Analysis of geometric accuracy from random errors 12 kA, R.ref = 21.55 mm 0.2 µΩ – 3.6 µΩ in HQ01e << 20 µΩ for LHC magnets best fit d0 = 29.6 µm. X. Wang

22. Quadrupole Design Optimization High field technology provides design options to maximize luminosity

23. Scaling-up to 150 mm Aperture • Based on results of LARP models at 90 and 120 mm, and preliminary studies for larger aperture, no serious difficulties are anticipated for the 150 mm aperture IR quadrupole design, but some optimization is required • Conductor and cable: increase cable width from 14.8 mm to 18.5 mm to facilitate coil stress management and quench protection • Increase strand diameter from 0.778 to 0.85 mm to limit cable aspect ratio • Preliminary cable dimensions established for 0.85 mm wire: 18.5 mm width, 1.50 mm mid-thickness, 0.65 deg. keystone angle (D. Dietderich) • ~30 kg of 0.85 mm wire expected for mid-July, fabrication of prototype cable planned for this summer • Electrical integrity: high voltage testing requirements were established, and an increase of cable insulation thickness from 0.1 mm to 0.15 mm is planned • At this time, the key elements to start the cross-section design are available • An increase of the cold mass diameter from 57 cm to 63 cm was also approved as baseline, providing a key parameter needed to start the mechanical design

24. Summary • A large knowledge base is available after 7 years of fully integrated effort involving three US Labs and CERN • Demonstrated all fundamental aspects of Nb3Sn technology: • - Steady progress in understanding and addressing R&D issues • The remaining challenges have an increasingly programmatic flavor: design integration, production organization and processes • HL-LHC IR Quads are a key step for future high-field applications • Next few years will be critical and much work is still left to do • - Integrate effort with CERN, EuCARD, KEK, US core programs Acknowledgement