nb 3 sn ir quadrupoles for hl-lhc

ASC 2012 Nb3Sn IR Quadrupoles for HL-LHC – G. Sabbi 1

Nb3Sn IR Quadrupoles for HL-LHC

BNL - FNAL - LBNL - SLAC

GianLuca Sabbi

for the US LHC Accelerator Research Program

2012 Applied Superconductivity Conference


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 *• 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


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


Material NbTi Nb3Sn

Dipole Limit ~ 10 T ~ 17 T

Reaction Ductile ~ 6750C

Insulation Polymide S/E Glass

Coil parts G-10 Stainless

Axial Strain N/A ~ 0.3 %

Transverse stress N/A ~ 200 MPa

Transverse Stress (MPa)

Ca

ble

Crit

ica

l Cu

rre

nt

(kA

)

Brittleness:• React coils after winding• Epoxy impregnation

Strain sensitivity:• Mechanical design and analysis to prevent degradation under high stress

Nb3Sn Technology Challenges


R&D Program Components

Long QuadrupoleLQS3.7 m long90 mm bore

Long High-Field Quadrupole (LHQ)120 mm bore – Length TBD (3.5-4.5m)

Long QuadrupoleLQS3.7 m long90 mm bore

Long High-Field Quadrupole (LHQ)120 mm bore – Length TBD (3.5-4.5m)

SM

TQS

HQ

LR

LQS

LHQ

• Racetrack coils, shell based structure• Technology R&D in simple geometry• Length scale up from 0.3 m to 4 m

• Cos2 coils with 90 mm aperture • Incorporation of more complex layout• Length scale up from 1 m to 4 m

• Cos2 coils with 120 mm aperture• Explore force/stress/energy limits• Nb3Sn Technology Demonstration


Overview of LARP Magnets

SQSM TQS

LR

LQS

HQTQC


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



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



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


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


Handling High Stress in Magnet Coils

Titanium pole

1. Understand limits 2. Optimize structure and coil for minimum stressTQ (90 mm, ~12 T) LQ (90 mm, ~12 T) HQ (120 mm, ~15 T)

4.5K, 0T/mSSL preload



Key location Coil geometry

200 MPa 170 MPa 190 MPa

170 MPa180 MPa


Technology Quadrupole (TQ)

• Double-layer, shell-type coil• 90 mm aperture, 1 m length• Two support structures:

- TQS (shell based)- TQC (collar based)

• Target gradient 200 T/m

Winding & curing (FNAL - all coils) Reaction & potting (LBNL - all coils)

TQC TQS


TQ Studies: Stress Limits

-180

-160

-140

-120

-100

-80

-60

-40

-20

0

Assembly Cool-down Gss (239 T/m)

MPa Pole (middle & range) Midplane (middle & range)

Coil layer 1 stress evolution -

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 higherConsiderably widens design window

260 MPa @ 4.5K

255 MPa @ SSL

Calculated peak stresses in TQS03c


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


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

Aluminum collar

Bladder location

Aluminum shellMaster key

Loading keys

Yoke-shell alignment

Pole alignment key

Quench heater

Coil


Mechanical Design Space in HQ models

• 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

Pole quenches (HQ01d) Pole stress during ramp to quench (HQ01d)

Mid-planeQuenches(HQ01d)


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


Performance issues in early HQ Tests

Time (s)

Extr

actio

n Vo

ltage

(V)

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

HQ01b extraction voltageHQ01a-d Ramp Rate dependence

M. Martchevsky


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

Coil spring back in tooling (Over) size measurements of completed coil

H. Felice, G. Ambrosio, R. Bossert, R. Hafalia, J. Schmalzle


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

Ramp rate dependence

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?


Field Quality Studies in HQ01d-e

X. Wang

• 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

1.E-03

1.E-02

1.E-01

1.E+00

1 2 3 4 5 6 7 8 9 10

harm

onics

σ

(uni

ts)

Harmonic order

fit

normal

skew

12 kA, R.ref = 21.55 mm best fit d0 = 29.6 µm.

Analysis of geometric accuracy from random errors

0.2 µΩ – 3.6 µΩ in HQ01e << 20 µΩ for LHC magnets


Quadrupole Design Optimization

HigherField

Larger Aperture(at same gradient)

Thicker absorbers

More Operating Margin(at same gradient / aperture)

Longer Lifetime

Lower radiation and heat loads

Better Field Quality

Better beam optics

Higher Gradient(at same aperture)

Shorter magnets

Higher T margin

Better IR layout

Stable operation

Easier cooling

More Design Margin(same gradient / aperture) Lower risk

Faster developmentLess cost & timefor small production

More luminosity

High field technology provides design options to maximize luminosity


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


Summary

Acknowledgement

• 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

nb 3 sn ir quadrupoles for hl-lhc

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