Geneva – 4 th November2008

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Geneva – 4 th November2008 Bernardo Bordini Guidelines on Magneto-Thermal Stability

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Geneva – 4 th November2008. Guidelines on Magneto-Thermal Stability. Bernardo Bordini. OUTLINE. INTRODUCTION SELF-FIELD INSTABILITY IN STRAND MEASUREMENTS CONDUCTOR REQUIREMENTS TO AVOID INSTABILITIES IN MAGNETS CONCLUSIONS. HIGH - J c Nb 3 Sn STRAND AND MAGNETO-THERMAL INSTABILITIES. - PowerPoint PPT Presentation

Transcript of Geneva – 4 th November2008

Page 1: Geneva – 4 th  November2008

Geneva – 4th November2008

Bernardo Bordini

Guidelines on Magneto-Thermal Stability

Page 2: Geneva – 4 th  November2008

04/November/2008 Bernardo Bordini 2

OUTLINE

INTRODUCTION

SELF-FIELD INSTABILITY IN STRAND MEASUREMENTS

CONDUCTOR REQUIREMENTS TO AVOID INSTABILITIES IN MAGNETS

CONCLUSIONS

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HIGH -Jc Nb3Sn STRAND AND MAGNETO-THERMAL

INSTABILITIES

High-Jc Nb3Sn wires is the best candidate for next generation High Field (>10 T) accelerator magnets

Although very promising, state of the art high-Jc Nb3Sn wires suffer flux jumps

Flux jumps can quench the superconductor and severely limit the strand performance

Flux jumps are caused by magneto-thermal instabilities:1) ‘Magnetization’ instability depending on Jc , Deff and Cu RRR

2) ‘Self field’ instability depending on Jc and strand diameter

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04/November/2008 Bernardo Bordini

MAGNETO-THERMAL INSTABILITIES AND MAGNET

PERFORMANCEMagnetization instability has been the primary cause of the limited quench performance (40-70 % of the short sample limit) at 4.4 K of some Nb3Sn high field magnets built at FNAL [1] and LBNL [2] in the early 2000sAt present the problem of magnetization instability at 4.4 K is contained through optimized heat treatments and cabling processes that guarantee a high RRR

4

RRR 8 RRR 120

[1] A. V. Zlobin et al , “R&D of Nb3Sn Accelerator Magnets at Fermilab”, IEEE Trans. Appl. Supercond., vol. 15, no. 2, Jun. 2005

[2] D. R. Dieterich et al , “Correlation between strand stability and magnet performance”, IEEE Trans. Appl. Supercond., vol. 15, no. 2, Jun. 2005

Strand diam.[mm]

Strandtype

Jc @ 4.2 K-12 T

[A/mm2]

Bc2 @4.2 K[T]

Deff

[μm] RRR

0.8 RRP® 2602 24.54 80 82645 23.56 120

B. Bordini, L. Rossi, presented at Applied Superconductivity Conference, Chicago, USA, Aug. 2008

Strand measurements at 4.3 K performed at CERN

B. Bordini, E. Barzi, S. Feher, L.Rossi, A.V. Zlobin, IEEE Trans. Appl. Supercond., vol. 18, no. 2, pp. 1309 - 1312, Jun. 2008

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04/November/2008 Bernardo Bordini

MAGNETO-THERMAL INSTABILITIES AND MAGNET

PERFORMANCERecently, it has been shown that at 1.9 K the self field instability is the dominating mechanism that limits the performance of high-Jc Nb3Sn strands [1]; this instability might be the primary cause of premature quenches of HF magnets at 1.9 K

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[1] B. Bordini, E. Barzi, S. Feher, L.Rossi, A.V. Zlobin, “Self-Field Effects in Magneto-Thermal Instabilities for Nb-Sn Strands”, IEEE Trans. Appl. Supercond., vol. 18, no. 2, pp. 1309 - 1312, Jun. 2008[2] B. Bordini, M. Bajko, H. Felice, C. Giloux, L. Rossi, “A Test Procedure to Study the Magneto-Thermal Stability around 1.9 K of TQS02c, a 1 m long Nb3Sn Quadrupole Magnet”, CERN Internal Note

Strand Measurements 0.8 mm RRP – RRR 80 Test of the

TQS02c Magnet at CERN [2]

4.3 K - Iq/Iexpected=11.9 K - Iq/Iexpected=0.7

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WHAT IS THE SELF-FIELD INSTABILITY ?

0.8 mm RRP® Nb3Sn strand

Simulation of the transport current distribution while increasing the current from 0 to 1200 A in a fixed applied field, Ba=6 T

While ramping up I at a fixed Ba , the multifilamentary strand acts as a large monofilament with a radius equal to the composite radius:The current only flows in the outermost sub-elements at the critical current density.

The self field instability is caused by the uneven distribution of transport current (I) within the wire.

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SELF-FIELD INSTABILITY :

Simulation of Premature Quench

The color represents the

Transport Current distributionBa=6 T -- I=1200 A --

Ti=4.2 K

The color represents the Temperature

distribution

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OUTLINE

INTRODUCTION

SELF-FIELD INSTABILITY IN STRAND MEASUREMENTS

CONDUCTOR REQUIREMENTS TO AVOID INSTABILITIES IN MAGNETS

CONCLUSIONS

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04/November/2008 Bernardo Bordini 9

V-I MEASUREMENTS Several samples of 0.8 mm 54/61 RRP® strands with similar Jc and significantly different RRR were test at 4.3 K and 1.9 KIncreasing the RRR up to 150 improves the stability of the strand; further increasing the RRR does not produce significant changesIs-SF = Self Field Stability Current ; Is-SF (4.2 K)>Is-SF (1.9K)<Ic (12T,1.9K)In one case: Is-SF (1.9K)=0.68 Ic (12T,1.9K)<Ic (12T,4.2K) High RRR is not sufficient to prevent Self Field Instability in 12 T magnetsStrand measurements show that the self field stability of the strand can be improved :

Reducing the strand diameterDecreasing the Jc

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ARE STRAND MEASUREMENTS REPRESENTATIVE OF THE

CONDUCTOR BEHAVIOUR IN THE MAGNET?Self-field instability is sensitive to the perturbation energy that initiates the

instability*Strand measurements cannot perfectly reproduce the conductor behavior in the magnet; during strand measurements the conductor is generally more stable because the perturbations are smallerStrand measurements at 1.9 K:

54/61 RRP 0.8 mm RRR 80 (S.3) and 8 (S.4)Simulations at 1.9 K using a new Finite Element Model*: 54/61 RRP 0.8 mm RRR 8 - Pert. 100% 0.73 μJ/mm

*B. Bordini, L. Rossi, “Self field instability in high-Jc Nb3Sn strands with high Copper Residual Resistivity Ratio”, presented at Applied Superconductivity Conference, Chicago, USA, August, 2008

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OUTLINE

INTRODUCTION

SELF-FIELD INSTABILITY IN STRAND MEASUREMENTS

CONDUCTOR REQUIREMENTS TO AVOID INSTABILITIES IN MAGNETS

CONCLUSIONS

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EFFECTS OF LOCAL STRAND’S DAMAGES

0

200400

600

8001000

1200

1400

16001800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law Iq Data - Sample with burst Bq Data- Sample with burstIq DataBq Data

No quench: Reached

System Limit

0

200400

600

8001000

1200

1400

16001800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law Iq Data - Sample with burst Bq Data- Sample with burstIq DataBq Data

No quench: Reached

System Limit

LARP 54 /61 RRP 0.7 mm RRR > 250

A small local damage of the copper stabilizer can completely jeopardize the dynamic stabilization of a high Jc Nb3Sn strand Sample holder

diameter ~ 32 mm

1.9 K

4.2 K

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Magnet Designed to Operate at 4.3 K – Jc 2000

A/mm2

*B. Bordini, E. Barzi, S. Feher, L.Rossi, A.V. Zlobin, “Self-Field Effects in Magneto-Thermal Instabilities for Nb-Sn Strands”, IEEE Trans. Appl. Supercond., vol. 18, no. 2, pp. 1309 - 1312, Jun. 2008

Under adiabatic assumptions, the Magneto-Thermal Stability of a Magnet that has to operate at its critical current depends on: the expected peak field at a certain temperature, the strand diameter, the effective filament sizes and the conductor critical current densityCalculations based on a semi-analytical model* using the layout of RRP strands (Cu/nonCu~1; composite radius ~ 80% strand radius)The colored (black) lines represent the ratio between the stability current due to magnetization instability (self field) and the conductor critical current

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Magnet Designed to Operate at 4.3 K – Jc 2000

A/mm2

ADIABATIC SIMULATIONS

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Magnet Designed to Operate at 4.3 K – Jc 2600

A/mm2

ADIABATIC SIMULATIONS

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Magnet Designed to Operate at 4.3 K – Jc 3000

A/mm2

ADIABATIC SIMULATIONS

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Magnet Designed to Operate at 1.9 K

Different colors different strand (assumption composite radius ~ 80% strand radius – RRP strand)A magnet that has to reach its critical current when the peak field is 15 T and the temperature is 1.9 K have to use strands with a composite diameter ≤ 0.8*0.8 mm (adiabatic approximation)

ADIABATIC SIMULATIONS

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CONCLUSIONS

Increasing the RRR above 150 does not improve the conductor magneto-thermal stabilityA local damage of the copper stabilizer can completely Jeopardized the dynamic stabilization of the conductor we can not relay on the dynamic stabilization is better to design a magnet assuming a low RRR value High-Jc Nb3Sn conductor (Jc >2600 A/mm2 at 4.2 K and 12 T) is not perfectly suitable for 12 T magnets because of magneto-thermal instabilities; this problem disappears if we move towards higher field magnets Magneto-thermal instability is not a problem for 15 T magnets that have to operate at 4.3 K (as Fresca2) if the strand diameter () and the effective filament size (Deff ) are sufficiently small ( ≤ 1 mm, Deff ≤ 70 μm)A 15 T magnet designed to work at 1.9 K could still have problems if the strand diameter and the Jc are not sufficiently small (for an RRP strand Jc =2600 A/mm2 at 4.2 K and 12 T ≤ 0.7 mm); for larger strands and Jc we have to improve the strand layout.

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CONCLUSIONS

Increasing the RRR above 150 does not improve the conductor magneto-thermal stabilityA local damage of the copper stabilizer can completely Jeopardized the dynamic stabilization of the conductor we can not relay on the dynamic stabilization is better to design a magnet assuming a low RRR value High-Jc Nb3Sn conductor (Jc >2600 A/mm2 at 4.2 K and 12 T) is not perfectly suitable for 12 T magnets because of magneto-thermal instabilities; this problem disappears if we move towards higher field magnets Magneto-thermal instability is not a problem for 15 T magnets that have to operate at 4.3 K (as Fresca2) if the strand diameter () and the effective filament size (Deff ) are sufficiently small ( ≤ 1 mm, Deff ≤ 70 μm)A 15 T magnet designed to work at 1.9 K could still have problems if the strand diameter and the Jc are not sufficiently small (for an RRP strand Jc =2600 A/mm2 at 4.2 K and 12 T ≤ 0.7 mm); for larger strands and Jc we have to improve the strand layout.

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NO EFFECT OF EFFECTIVE FILAMENT SIZE AT ~1.9 K

MEASUREMENTS BY A. Ghosh (BNL)COURTESY OF D. Dietderich (LBNL)

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EFFECT OF STRAND LAYOUT ON SELF FIELD INSTABILITY AT

1.9 K

54/61 RRP Cu/non-Cu 0.93

288/295 PIT Cu/non-Cu 1.22

Preliminary results based on the more accurate new finite element model* (Dynamic Calculation) show that increasing the Cu/non-Cu ratio, the Cu volume between the sub-elements and reducing the sub-element size improve the strand stability but it not increase significantly the quench current

*B. Bordini, L. Rossi, “Self field instability in high-Jc Nb3Sn strands with high Copper Residual Resistivity Ratio”, presented at Applied Superconductivity Conference, Chicago, USA, August, 2008

0.8 mm wire – Jc (4.3 K, 12 T) ~ 2600 A/mm2

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V-I MEASUREMENTS: RRR ranging from 8 to

120Samples: four 0.8 mm 54/61 RRP® strands reacted in a way to have almost the same Jc with a significantly different RRR Is-SF (4.2 K)>Is-SF (1.9K)<Ic (12T,1.9K)Sample 3: Is-SF (1.9K)=0.68 Ic (12T,1.9K)<Ic (12T,4.2K) !

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12 13Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law - S. 1 & S. 3 Ic (or Iq) Data 20 A/s - S. 3Ic Scaling Law - S. 3 (Grease) Ic (or Iq) Data 20 A/s - S. 3 (Grease)Ic Scaling Law - S. 4 Ic (or Iq) Data 20 A/s - S. 4Ic (or Iq) Data 20 A/s - S. 1

No quench: Apparatus Limit

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12 13Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law - S. 1 & S. 3 Ic (or Iq) Data 20 A/s - S. 3Ic Scaling Law - S. 3 (Grease) Ic (or Iq) Data 20 A/s - S. 3 (Grease)Ic Scaling Law - S. 4 Ic (or Iq) Data 20 A/s - S. 4Ic (or Iq) Data 20 A/s - S. 1

No quench: Apparatus Limit 4.2

K1.9 K

SampleID

RRRJc @

4.2 K-12 T

[A/mm2]

Bc2* @

4.2 K[T]

S. 1 120 2580 23.06S. 3 80 2672 23.94S. 4 8 2564 24.54

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V-I MEASUREMENTS: RRR ranging from 140 to

290Samples: three 0.8 mm 54/61 RRP® strands reacted in a way to have almost the same Jc with a significantly different RRR larger than 120 Is-SF (4.2 K)>Is-SF (1.9K)Is-SF (1.9K)<Ic (12T,1.9K)

SampleID

RRRJc @

4.2 K-12 T

[A/mm2]

Bc2* @

4.2 K

[T]S. 5 290 2978 24.5S. 6 270 3030 24.92S. 7 140 2852 24.13

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law - S. 5 & 6 Iq Data 5A/s - S. 6Ic Scaling Law - S. 7 Iq Data 2A/s - S. 6 Ic (or Iq) Data 20A/s - S. 5 Ic (or Iq) Data 20A/s - S. 7Iq Data 5A/s - S. 5 Iq Data 10A/s - S. 7Ic (or Iq) Data 20A/s - S. 6 Iq Data 5A/s - S. 7

No quench: Apparatus Limit 1.9

K

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law - S. 5 & 6 Ic (or Iq) Data 20A/s - S. 6Ic Scaling Law - S. 7 Iq Data 5A/s - S. 6Ic (or Iq) Data 20A/s - S. 5 Ic (or Iq) Data 20A/s - S. 7Iq Data 5A/s - S. 5

No quench: Apparatus

Limit 4.2 K

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Samples 8 and 9, drawn at the University of Geneva, are significantly more self-field stable than sample 5, which is the most stable of the previous sample set (S. 1-7), thanks to:1) the smaller strand diameter (S. 8);2) the lower Jc and probably the

different strand layout (S. 9).The PIT strand (S. 9) adopted solutions that theoretically helps the dynamic stabilization of the strand

V-I MEASUREMENTS: Improving Self-Field Stability

0

1

2

3

4

5

0 1 2 3 4 5 6 7 8 9 10 11 12Applied Magnetic Field, Ba (T)

Nor

mal

ized

Cur

rent

, I n

Ic_n Data 5 & 20 A/s - S. 5Ic_n Data 5 & 20 A/s - S. 5Ic_n Data 5 & 20 A/s - S. 8Iq_n Data 20 A/s - S. 8Ic_n Data 5 & 20 A/s - S. 9Iq_n Data 20 A/s - S. 9

No quench: Apparatus Limit

SampleID

RRRIc @

4.2 K-12 T[A]

Jc @4.2 K-12 T

[A/mm2]

Bc2* @

4.2 K[T]

Deff

[μm]Strand diam.

[mm]

Strandtype

Cu/non-Cu

S. 5 290 777 2978 24.5 80 0.8 RRP 0.927S. 8 270 417 2842 23.4 60 0.6S. 9 27 508 2236 24.27 30 0.8 PIT 1.22

In=Iq/Ic(12T,4.2K)

1.9 K

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EFFECTS OF COOLING CONDITIONS ON INSTABILITIES

A thick layer of stycast did not change the critical current and did not significantly change the premature quench current values

600

800

1000

1200

1400

1600

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2000

0 1 2 3 4 5 6 7 8 9 10 11 12 13Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law Iq Data 20A/s - S. 2 (stycast)Ic (or Iq) Data 20 A/s - S. 2 Iq Data 10A/s - S. 2 (stycast)Iq Data 10 A/s - S. 2 Bq Data - S. 2 (stycast)Bq Data - S. 2

No quench: Apparatus Limit

54/61 RRP 0.8 mm RRR 120

600

800

1000

1200

1400

1600

1800

2000

0 1 2 3 4 5 6 7 8 9 10 11 12 13Applied Magnetic Field, Ba (T)

Cur

rent

, I (A

)

Ic Scaling Law Ic (or Iq) Data 20 A/s - S. 2 (stycast)Ic (or Iq) Data 20 A/s - S. 2 Bq Data - S. 2 (stycast)Bq Data - S. 2

1.9 K

4.2 K