High-strength, 20-T class Bi - PowerPoint Presentation

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High-strength, 20-T class Bi2Sr2CaCu2Ox cables for high-field magnets

Tengming Shen

,

for Fermilab teamMAP HTS magnets workshop, Fermilab, Batavia, IL, 60510May 30-31, 2012

Acknowledgements:

nGimat

/NCSU for experimental support.

BNL, NHMFL/FSU, LBNL, OST for collaboration.

U.S. DOE for funding support.

OutlineCable allows large magnets.Can high current, high-strength cable be made from Bi2Sr2CaCu2Ox without sacrificing the precious superconducting current carrying capability?It has broad applications.

Yes. We have designed, manufactured, and tested 9 m of such cable.

Constructing >30 T all superconducting magnets will needLong-length superconductors that can carry high current density in strong magnetic fieldsVHFSMC breakthrough: Bi-2212 round wire can carry ~600 A/mm2 at 4.2 K, 20 T.Eliminating gas impurities is key to develop high J

c in long length wire.

Sufficient mechanical structure to handle large electromagnetic stressesMagnetic pressure goes up with B2.The current-carrying capability of superconductor is sensitive to its strain state.Intelligent quench detection and protection to discharge magnet current quickly

For preventing hot-spot temperature rise to dangerous levels.

High-strength, high-current cable can help.

Protection becomes a serious business for those magnets with stored energy Em above ~100 kJBecause magnet can’t withstand infinite large voltage during dischargingAnd discharging time is often needed to be <5 seconds.

With considerable stored energy, large high field magnets are often constructed from high current cables for reducing magnet inductance and making protection easier.

Final cooling solenoids are expected to have stored energy of > several MJ.

Round wire 2212 allows fabrication of versatile high-current, 20-T class cables for high-field magnet applicationsGreen wire

6+1

4+3

3+4

CICC-like cable for >30 T solenoids for Muon Collider

Rutherford cable for >20 T dipoles for HE-LHC

Arno Godeke

Superconductor

High-strength

material

The high-strength, 20-T class cables from a high-temperature superconducting material have many merits and have been explored for many applications 2212 (6+1)-type cable for 30+ T muon collider final cooling magnetsReduce the risks associated with local degradations of single-strand.Increase stability margin by several-fold compared to single-strand.

Reduce difficulties associated with quench protection.Smaller magnet inductance allows faster magnet current decay while keeping the magnet voltage to a safe level.

Can be internally reinforced with high-strength alloys to handle the high electromagnetic stresses in high-field magnets.Such cables have been explored for building magnetic energy storage devices and high-field magnets by many groups butCored cables made till today suffer severe degradations associated with complicated chemical interactions between 2212 and structural materials used.

6+1

4+3

3+4

High-strength cable for high field magnets

Successful material selection is a key as the cable package needs to go through a high-temperature reaction up to 890 °C in O2Structural and other materials need toMaintain good mechanical properties after a 890 °C heat treatment.Be chemically compatible with 2212 so a >95% of 2212 Jc can be maintained.

Effect of 2212 heat treatment on mechanical properties of selected high-temperature alloys

Alex Matta, FNAL-SIST, 2011 summer student

Structural properties of reacted alloy wires, as compared to that of reacted 2212Alex Matta, FNAL-SIST, 2011 summer student

6 Alloy wires + bare 2212

Experimental scheme for testing material compatibility

Note: alloy wires were pre-oxidized in flowing O

2

(1) at 700 °C for 2 h, and (2) a standard 2212 heat treatment cycle with T

max

=890 °C.

Two materials were found to be fairly compatible with 2212 chemically

Bi9 (Sr, Ca)16

OxCu-free phase

2212/

NiCr

2212/Alloy-X

2212/Inconel 600

2212/

Inconel

X750

Cu leaving 2212 induced by Inconel alloys.

Mechanism by which J

c

was reduced in the case of Inconel 600 and X750 is identified

Reducing chemical incompatibility by coating alloys wires with a protective oxide layer

6 Alloy wires + oxide coated 2212

Note: alloy wires were pre-oxidized in flowing O

2

(1) at 700 °C for 2 h, and (2) a standard 2212 heat treatment cycle with T

max

=890 °C.

TiO

2

layer

We would like to thank

nGimat

/NCSU for their help with TiO

2

coating.

Coating 2212 with an oxide layer is effective in eliminating the formation of surface cracks on 2212 wires

We have developed a cable that minimizes the poison and other negative effects from structural materialsWe have carefully studied the chemical interactions between 2212 and many high-temperature, high-strength materials, and selected a material that is chemically compatible with 2212 and that can maintain high strength even after a 890 °C high-temperature reaction in O2.>95% of J

c was maintained in mock-up short-sample tests Fermilab

has designed and manufactured 9 m demonstration cables.

High strength

alloy wire

Oxide

protection

layer

Bi-2212 round wire

High Strength 6+1 Bi-2212 cable

Before reaction:

We would like to thank strand-and-cable engineering group at Fermilab for cable manufacturing.

Cables are clean and free of leakages after reactions8 cm sample:

Meter-long barrel sample:

Transport measurements showed that our cable attains 105% Jc of that of the single-strand

I-V curves of strand and cable barrels at 4.2 K, 5 T

Summary and OutlookWe developed high-strength, Bi2Sr2CaCu2Ox

cable that fully retained the superconducting current-carrying capability of Bi2Sr2CaCu2

Ox strand.Suitable for high-field magnets: make easier the stress management and quench protection.Reaction and test of demonstration coils are among the planned works.

We will be moving towards 10 kA, 20-T class cables by bringing recently-achieved short-sample JE of ~600 A/mm2 at 4.2 K, 20 T to long-length.

A critical step to demonstrate the feasibility of large-size, >20 T all superconducting magnet system.