Transverse Pressure on Rutherford Cables A Concise Review and New Experiments

Transverse Pressure on Rutherford CablesA Concise Review and New Experiments

A. Godeke1, D. Arbelaez1, D.R. Dietderich1, S.O. Prestemon1,

F. Trillaud1, G. Miller2, H.W. Weijers2

1Lawrence Berkeley National Laboratory

2National High Magnetic Field Laboratory

LARP Meeting – Napa, CAApril 8, 2009

Funded by the US Department of Energy under contract No. DE-AC02-05CH11231

A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 2/18

The early years: Lessons learned…

First (?) full size cable measurements on ECN-PIT

Early conclusions:

Cable needs to be well impregnated

Initial (sharp) reduction (A) due to strands crossing under pressure block

Irreversible damage (cracks) occur only at cable edges

Edges and impregnation are key determinants

Boschman et al, IEEE Trans. Magn. 27, 1831 (1991)

Sample 2 after 300 MPa

Edge Center#1: Not impregnated

#2: Impregnated

A

Global and local V-taps


Increasing statistics…

All data below were reproduced on a second sample

TWCA MJR showed unusual large reductions

ECN-PIT

VAC-Bronze

TWCA-MJR 26TWCA-MJR 48

Ten Kate et al, IEEE Trans. Appl. Supercond. 3, 1334 (1993)Van Oort et al, IEEE Trans. Appl. Supercond. 3, 559 (1993)


Relevance of cable edge deformation

TWCA MJR sensitive to narrow edge deformation during cabling

All normalized Ic values at 150 MPa transverse load

ECN-PIT and VAC-Bronze less sensitive to narrow edge deformation

Van Oort et al, Adv. Cryo. Eng. 40, 867 (1994)


Reproducibility

Rectangular vs. keystoned; Twente vs. LBNL/NHMFL (described later)

Twente on EM-LMI ITGodeke et al, report 1996

Twente vs. LBNL/NHMFL on IGC IT and TWCA MJRDietderich and Godeke, Cryogenics 48, 331 (2008)

Quench values

Bauer et al, IEEE Trans. Appl.Supercond. 11, 2457 (2001)ITER-type IGC-IT @ NHMFL

11 T data


Issues and findings

Collective Twente experiences Good impregnation is keyEpoxy = training, Stycast = no training

G10 on top and bottom yields more consistent results

Compaction dependence less for ECN and Bronze, more for MJR-IT

Visible damage always at (thin) edge

Pressure block alignment is sometimes issue

15 to 20 cables measured

10 to 20% of results are suspect

Large reductions mostly attributable toExperimental error (impregnation, alignment, load homogenization,…)

Over-compaction of cable edges (MJR)


The bottom line…

Full size cable transverse pressure sensitivity for < 2 kA/mm2 conductors

At 11 T applied magnetic field, Ic data

200 MPa reduction is almost completely reversible, even for IGC-IT

Where does RRP fit in this table?

Cable type 100 MPa Ic reduction 200 MPa Ic reduction

ECN-PIT 2 – 4% 5 – 8%

EM-LMI-IT(?) 2 – 3% 6 – 7%

TWCA-MJR 3 – 5% 5 – 11%

VAC-Bronze 7 – 10% 18 – 22%

IGC-IT ~ 5% 38 – 46%

IGC “ITER-type” IT ~ 12% ~ 20% (est.)


0.2

0.4

0.6

0.8

1

1.2

0 30 60 90 120 150 180Transverse Pressure, MPa

No

rmal

ized

Cri

tical

Cu

rren

t

. 0.7 mm 54/61 88.5% PF

0.7 mm 54/61 85.0% PF

1 mm 114/127 85.1% PF

1 mm 114/127 85.1% PF

Modern single strand in cable results (FNAL)

Single SC strand in Cu dummy cable:

No side support; impregnated?

MJR and ITER: 80 – 150 MPa

PIT: 50 – 90 MPa

PIT w/ core: ~ 140 MPa

Barzi et al, Adv. Cryo. Eng. 48, 45 (2002)Barzi et al, IEEE Trans Appl. Supercond. 15, 1544 (2005)Barzi et al, IEEE Trans Appl. Supercond. 18, 980 (2008)

12 T

RRP limit 60 – 90 MPa


Axial strain sensitivity

“Medium current” wires show reversible axial strain dependence, also in tensile

High current RRP cracks when taken into the tensile region

Identical RRP data at NIST and Twente

Constant current at 15 T

RRP

RRP

ITER Furukawa

12 T

Godeke et al, Supercond. Sci. Techn. 19, R100 (2006)Godeke et al, ASC-2008


Loads in magnets using high Jc RRP wire - I

HD1

Computed from measured shell tension

160 MPa load levels

Inside and outside

HD2

Computed from measured shell tension

160 MPa load levels

170 MPa in outsideregion layer 1

X=0…50

Layer 2

P. Ferracin, LBNLP. Ferracin, LBNL


Loads in magnets using high Jc RRP wire - II

Stress levels in TQS01 and TQS02

Strain gauge measurement on island

Azimuthal stress levels ~ 150 MPaS. Caspi, LBNL


New strand results question suitability Nb3SnAll older generation cables: 200 MPa OK

Single RRP strand in Cu cable: irreversible reduction above 60 – 90 MPa

Magnets: 150+ MPa is OK and reversible

Axial strain experiments: Cracks occur in tensile strain region

Is high Jc RRP indeed more sensitive to transverse pressure, or doconclusions depend on experimental details?

Full size cable measurements needed

New cable measurements by LBNL/NHMFL

Full size cable measurements

Pressure up to 200 MPa NHMFL load system

Magnetic field up to 12 T NHMFL split pair solenoid

Current up to 25+ kA

NHMFL house supply: Noise, sample protection, scheduling, high LHe loss

SC transformer: Quiet, intrinsic sample protection, available, low LHe loss


LBNL/NHMFL cable holder

2 active cables sandwiched between 2 dummy cables

~3 foot long samples

Soft load transition

~120 mm loaded region

Displacement meters

Strain transducers

Strain gauges on I-beam

Force transducers

Piston pressure


Implementation in NHMFL system

Current supplied by SC transformer (50 A 50 kA)


Transformer specs and control

High accuracy, 15 kHz bandwidth, inductive current meter

High accuracy, negligible drift, digital integrator for current meter

Active feedback system controls Isec and auto-compensates for losses

Commissioned up to 28 kA (limited during initial test)

V~dIs/dt

V~Is

Vset Is


System implemented at the NHMFL

Two LARP cable measurements: April 27 – May 1

Need to determine cable Ic(field,pressure)

Cable tests – Funds need to be reserved for more tests later this fiscal year

NHMFL: Jc(B,F_|_) w/ cold load adjustFirst test campaign April 27, 2009

Further tests required

Statistics and variance in cables/strands

CERN: Jc(B, F_|_) at RT + cool-down2006 LBNL concept implemented at CERN

RT load w/ bladders

Cool-down increases load

As in Shell structure

Fall 2009 (Ambrozio)

Ti

Kapton or vacuumStainless

Bladder

Key

G10

Cable x 2

Ti

Kapton or vacuumStainless

Bladder

Key

G10

Cable x 2


Planning / needs / desirablesCable tests

Past experience highlights importance of statistics

Cable tests need to be an integral part of Nb3Sn magnet developmentTransverse load limit is key determinant in magnet design

Transformer cost effective tests, independent of NHMFL current supplyNHMFL pressure system needs improvement

Connection strand data cable data magnet performance“Straightened” extracted strands on ITER barrels a good method?

Comparisons with non-straightened samples (desired) and cables (needed)

Can cable tests be replaced by more cost effective single strand F_|_ tests?Differences need to be analyzed, alternatives need consideration

Strong indications for tensile strain issues in RRP materialMore axial strain tests are needed to accurately map this

3D strain models require expansion and refinement


Summary

Determine transverse load limit in full size cables (HQ 177 MPa?)New capabilities to perform cost effective full size cable measurements

Jc cable vs. extracted strandsJc cable vs. pressure gives magnet design criteria

Need increased testing resourcesStatistics on Jc(pressure), reliability NHMFL load system, non-straightened vs. straightened extracted strands vs. cables vs. magnets, axial strain, strain models

Cable type 100 MPa Ic reduction 200 MPa Ic reduction

ECN-PIT 2 – 4% 5 – 8%

EM-LMI-IT(?) 2 – 3% 6 – 7%

TWCA-MJR 3 – 5% 5 – 11%

VAC-Bronze 7 – 10% 18 – 22%

IGC-IT ~ 5% 38 – 46%

IGC “ITER-type” IT ~ 12% ~ 20% (est.)

OST-RRP TBD TBD

Transverse Pressure on Rutherford Cables A Concise Review and New Experiments

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