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Transverse Pressure on Rutherford Cables A Concise Review and New Experiments

Transverse Pressure on Rutherford Cables A Concise Review and New Experiments A. Godeke 1 , D. Arbelaez 1 , D.R. Dietderich 1 , S.O. Prestemon 1 , F. Trillaud 1 , G. Miller 2 , H.W. Weijers 2 1 Lawrence Berkeley National Laboratory 2 National High Magnetic Field Laboratory

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Transverse Pressure on Rutherford Cables A Concise Review and New Experiments

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  1. 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 Energyunder contract No. DE-AC02-05CH11231

  2. 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 The early years: Lessons learned… Boschman et al, IEEE Trans. Magn. 27, 1831 (1991) A Sample 2 after 300 MPa #2: Impregnated #1: Not impregnated Edge Center Global and local V-taps A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 2/18

  3. 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 3/18

  4. 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 4/18

  5. Reproducibility • Rectangular vs. keystoned; Twente vs. LBNL/NHMFL (described later) Quench values 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 5/18

  6. 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) Issues and findings A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 6/18

  7. 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? A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 7/18

  8. 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 Modern single strand in cable results (FNAL) • RRP limit 60 – 90 MPa 12 T 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 Transverse Pressure on Rutherford Cables 8/18

  9. “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 Axial strain sensitivity ITER Furukawa 12 T RRP RRP Constant current at 15 T Godeke et al, Supercond. Sci. Techn. 19, R100 (2006) Godeke et al, ASC-2008 A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 9/18

  10. 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 Loads in magnets using high Jc RRP wire - I X=0…50 P. Ferracin, LBNL P. Ferracin, LBNL Layer 2 A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 10/18

  11. 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 Transverse Pressure on Rutherford Cables 11/18

  12. 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 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 A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 12/18

  13. 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 Transverse Pressure on Rutherford Cables 13/18

  14. Implementation in NHMFL system • Current supplied by SC transformer (50 A  50 kA) A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 14/18

  15. 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 15/18

  16. 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 RT load w/ bladders Cool-down increases load As in Shell structure Fall 2009 (Ambrozio) System implemented at the NHMFL A. Godeke – LARP Meeting – Napa CA, April 8, 2009 Transverse Pressure on Rutherford Cables 16/18

  17. 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 17/18

  18. 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 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 Transverse Pressure on Rutherford Cables 18/18

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