Design of Nb 3 Sn IR quadrupoles with apertures larger than 120 mm

Design of Nb3Sn IR quadrupoles with apertures larger than 120 mm

Paolo Ferracin and Ezio Todesco

1st HiLumi LHC / LARP Collaboration Meeting CERN

16-18 November, 2011

Introduction• Upgrade of the LHC IR quadrupoles

– From Nb-Ti 70 mm bore (MQXA from Japan, MQXB from US) to larger apertures

• Currently under development, 120 mm aperture quadrupoles– Nb-Ti: MQXC (CERN-CEA Collaboration)– Nb3Sn: HQ - MQXE (US LARP Collaboration)

• Larger aperture under consideration for Nb-Ti (MQXD) and Nb3Sn (MQXF)

• Preliminary design study of MQXF, a 140 mm aperture Nb3Sn quadrupole

06/02/2011Paolo Ferracin 2

HQ

MQXC

Goals

• Investigate magnet parameters of an HQ-type quad. with the HQ cable and 140 mm aperture– How much do we lose in gradient?– How much do we increase the stress?

• Analyse the potential benefits of using a wider cable than HQ


Outline

• From HQ to MQXF

• Magnet parameters

• Stress analysis

• Conclusions


HQ

• Shell-based support structure– Pre-loaded with bladders– OD 570 mm, 1 m long

• Design focused on pre-load and alignment


• Five assemblies and tests at 4.4 K carried out

• Max. grad. achieved: 170 T/m– 11.7 T estimated peak field– 86% of Iss at 4.4 K

From HQ to MQXFMagnetic design concept

• Two cases considered: 15 and 17 mm wide cable• 2 layers with similar angles and 4 blocks• All harmonics below 1 unit at 2/3 of Rin and 80% Iss

• Similar iron geometry with OD = 520 mm


HQ MQXF_17mmMQXF_15mm

From HQ to MQXFMechanical design concept

• Same support structure concept as HQ• Same shell OD and thickness • Larger coil OD (aperture + thickness)• Collar-pad-yoke thickness reduced by 10 to 15 mm


HQ MQXF_15mm MQXF_17mm

Outline

• From HQ to MQXF


• Stress analysis

• Conclusions


Strand properties

• 0.8 mm strand, 108/127• 53% Cu -> Cu/Su: 1.13

• Extr. strand meas. (HQ coil 3-4)– Jc (4.2 K, 12 T) of 3070 A/mm2 with

self field correction– This is considered a upper bound

for a production

• We assumed a Jc of 2800 A/mm2 with self field correction– This gives 2% reduction in gradient

(3 T/m) w.r.t. 3070 A/mm2


Cable and coil parameters

• From HQ to MQXF_15mm– 11% more conductor

• From MQXF_15mm to 17mm– 16% more conductor


Units HQ MQXF_15 mm MQXF_17 mm

Strand # 35 35 40

Thickness in/out mm 1.338/1.536 1.338/1.536 1.338/1.536

Width mm 15.150 15.150 17.314

Insulation thickness mm 0.100 0.100 0.100

Turns per oct. 46 51 52

Area supercond. per oct. mm2 380 422 491

MQXF_15mm MQXF_17mm

Magnet parameters at 1.9 K

• From HQ to MQXF_15mm– Loss of 14% in gradient– 25% increase of stored energy

• 15mm or 17mm ?– Increase of gradient +3% with

16% more conductor and 15% more stored energy



Temperature K 1.9 1.9 1.9

Loadline margin % 20 20 20

Gradient T/m 169 145 149

Peak field T 11.7 11.9 12.1

Stored energy MJ/m 0.85 1.06 1.22

MQXF_15mm MQXF_17mm

Fringe field at 500 mm from the center

• W.r.t. Nb-Ti version, smaller yoke OD (520 mm) – Thicker shell (25 mm), and still missing the LHe vessel (5-10 mm thick)

• From HQ to MQXF_15mm– Fringe field from 0.68 to 9.77 T

• From MQXF_15mm to 17mm– Fringe field increases to 18.55 T

• Is it tolerable ? Is shielding necessary ? Further studies needed


80% Iss

HQ MQXF_15mm MQXF_17mm

Outline

• From HQ to MQXF


• Stress analysis

• Conclusions


Stress analysisThe HQ case at 169 T/m (80% of Iss)

• 2D comp. stress– Increase pre-load

during cool-down– Pole turn always under

pressure


Stress analysisThe HQ01e case: pole gauges measurements

• Pole azimuthal stress vs. I2 during training quench up to 170 T/m

• Linear variation up to maximum current

• No signs of unloading and pole-coil detachment



• Coil peak stress located in inner layer – Pole turn during bladder-key operation– Pole turn after cool-down– Mid-plane turn during excitation


Stress analysisComparison at 80% of Iss

• From HQ to MQXF_15mm– IL Lorentz stress: +13%– Peak stress: +15 MPa

• From MQXF_15mm to 17mm– Reduction of 10 MPa in peak

stress



IL OL IL OL IL OL

Lorentz stress MPa -100 -120 -113 -128 -108 -128

Axial forces and support• From HQ to MQXF_15mm

– Increase of axial force: 25%• From MQXF_15mm to 17mm

– Increase of axial force : 15%

• Axial support– Stainless steel end plate (50 mm thick)– Aluminum axial rods (34 mm diameter)

• Maximum rod stress in MQXF– 350 (80% of Iss) to 500 MPa (100% of Iss)



80% Iss 100% Iss 80% Iss 100% Iss 80% Iss 100% Iss

Axial force MN 0.85 1.32 1.06 1.63 1.22 1.87

Conclusions• A preliminary design of the 140 mm bore Nb3Sn quadrupole magnet MQXF

based on the HQ design has been carried out

• From HQ to MQXF (in operational cond.)– Gradient: from 169 to 145 T/m– Stored energy: from 0.85 to 1.06 MJ/m– Fringe field: from 0.68 to 9.77 mT – Peak stress: from 140 to 150 MPa

• According to a preliminary 2D mech. analysis, the HQ structure is capable provide pre-load to a 140 mm aperture coil up to Iss

• Increasing the cable by 2 mm provides additional 4 T/m with a reduction of 10 MPa in coil peak stress, but 15% more conductor and stored energy

• Next step– Further optimization of cable, coil, and support structure


Appendix


Stress analysisComparison at 100% of Iss

• Similar conclusions as at 80% of Iss

• Support structure– Bladder pressure

• Up to 55 MPa– Shell max stress

• Up to 340 MPa at 4.5 K– Iron maximum tension

• Below 200 MPa



IL OL IL OL IL OL

Lorentz stress MPa -154 -184 -173 -193 -167 -195

HQ parameters


MQXF_15mm parameters


MQXF_17mm parameters


Stress analysisCoil stress in TQ & HQ with e.m. forces at 1.9 K Iss

• Technology quadrupole TQ– 90 mm bore, 10 mm cable– Outer layer overcompressed

by -60 MPa at max. gradient

• High field quadrupole HQ– 120 mm bore, 15 mm cable– Inner and outer layer with

low stress at max gradient


0 MPa

-60 MPa

0 MPa

0 MPa


• Contact pressure (positive) coil-pole at 4.4 K

• Contact pressure (positive) coil-pole with e.m. forces


Saturation effect to Iss


Support structure options


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Design of Nb 3 Sn IR quadrupoles with apertures larger than 120 mm

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