Transcript Document 7482459

Transverse Pressure on Rutherford Cables
A Concise Review and New Experiments
A. Godeke1, D. Arbelaez1, D.R. Dietderich1, S.O. Prestemon1,
F. Trillaud1, G. Miller2, H.W. Weijers2
1Lawrence
2National
Berkeley National Laboratory
High Magnetic Field Laboratory
LARP Meeting – Napa, CA
April 8, 2009
Funded by the US Department of Energy under contract No. DE-AC02-05CH11231
The early years: Lessons learned…
First (?) full size cable measurements on ECN-PIT
A
Boschman et al, IEEE Trans.
Magn. 27, 1831 (1991)
Sample 2 after 300 MPa
#2: Impregnated
#1: Not impregnated
Edge
Center
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
Global and local V-taps
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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Increasing statistics…
All data below were reproduced on a second sample
TWCA MJR showed unusual large reductions
ECN-PIT
VAC-Bronze
TWCA-MJR 26
TWCA-MJR 48
Ten Kate et al, IEEE Trans. Appl. Supercond. 3, 1334 (1993)
Van Oort et al, IEEE Trans. Appl. Supercond. 3, 559 (1993)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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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)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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Reproducibility
Rectangular vs. keystoned; Twente vs. LBNL/NHMFL (described later)
11 T data
Twente on EM-LMI IT
Godeke et al, report 1996
Twente vs. LBNL/NHMFL
on IGC IT and TWCA MJR
Dietderich and Godeke, Cryogenics 48, 331 (2008)
Bauer et al, IEEE Trans. Appl.
Supercond. 11, 2457 (2001)
ITER-type IGC-IT @ NHMFL
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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Issues and findings
Collective Twente experiences
Good impregnation is key
Epoxy = 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 to
Experimental error (impregnation, alignment, load
homogenization,…)
Over-compaction of cable edges (MJR)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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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.)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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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
.
RRP limit 60 – 90 MPa
1.2
0.7 mm 54/61 88.5% PF
Normalized Critical Current
0.7 mm 54/61 85.0% PF
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)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
1
1 mm 114/127 85.1% PF
1 mm 114/127 85.1% PF
0.8
12 T
0.6
0.4
0.2
0
30
Transverse Pressure on Rutherford Cables
60
90
120
Transverse Pressure, MPa
150
180
8/18
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
RRP
ITER Furukawa
12 T
RRP
Godeke et al, Supercond. Sci. Techn. 19, R100 (2006)
Godeke et al, ASC-2008
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Constant current at 15 T
Transverse Pressure on Rutherford Cables
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Loads in magnets using high Jc RRP wire - I
HD1
Computed from measured shell tension
160 MPa load levels
Inside and outside
P. Ferracin, LBNL
HD2
Computed from measured shell tension
160 MPa load levels
170 MPa in outside
region layer 1
P. Ferracin, LBNL
Layer 2
X=0…50
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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Loads in magnets using high Jc RRP wire - II
Stress levels in TQS01 and TQS02
Strain gauge measurement on island
Azimuthal stress levels ~ 150 MPa
S. Caspi, LBNL
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
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New strand results question suitability Nb3Sn
All 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 do
conclusions 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
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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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
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
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Implementation in NHMFL system
Current supplied by SC transformer (50 A  50 kA)
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
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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)
Vset  Is
V~Is
V~dIs/dt
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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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 adjust
First test campaign April 27, 2009
Further tests required
Statistics and variance in cables/strands
CERN: Jc(B, F_|_) at RT + cool-down
2006 LBNL concept implemented at CERN
Kapton or vacuum
Key
RT load w/ bladders
Stainless
Ti
Cool-down increases load
Bladder
As in Shell structure
Fall 2009 (Ambrozio)
G10
Cable x 2
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
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Planning / needs / desirables
Cable tests
Past experience highlights importance of statistics
Cable tests need to be an integral part of Nb3Sn magnet development
Transverse load limit is key determinant in magnet design
Transformer  cost effective tests, independent of NHMFL current supply
NHMFL 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 material
More axial strain tests are needed to accurately map this
3D strain models require expansion and refinement
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
Transverse Pressure on Rutherford Cables
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Summary
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.)
TBD
TBD
OST-RRP
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 strands
Jc cable vs. pressure gives magnet design criteria
Need increased testing resources
Statistics on Jc(pressure), reliability NHMFL load system, non-straightened
vs. straightened extracted strands vs. cables vs. magnets, axial strain,
strain models
A. Godeke – LARP Meeting – Napa CA, April 8, 2009
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