# Presentation: 136115

## Superconducting Strand for High Field Accelerators

- _[Peter J. Lee ](http://www.cae.wisc.edu/~plee)_*and D. C. Larbalestier*
- _[The Applied Superconductivity Center](http://www.asc.wisc.edu/)_
*The University of Wisconsin-Madison*
- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Outline

- High Superconductor Options
- Alternatives to Nb3Sn
- 2212
- Nb3Al
- MgB2 (Recent Enhancements to *H*c2 at the UW)
- Nb3Sn
- Introduction to Fabrication Routes
- Increased Critical Current Density
- Where Does It Come From, What Are The Drawbacks
- Design Implications
- Summary of Recent Nb3Sn Results (UW)
- Conductor Issues

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## High Field Superconductors

**Critical Current**

**Density, A/mm2**

**10**

**100**

**1,000**

**10,000**

**10**

**15**

**20**

**25**

**30**

**Applied Field, T**

**Nb-Ti: Nb-47wt%Ti, 1.8 K, Lee, Naus and Larbalestier**
**UW-ASC'96**

**Nb-44wt.%Ti-15wt.%Ta: at 1.8 K, monofil. high field optimized,**

**unpubl. Lee, Naus and Larbalestier (UW-ASC) '96**

**Nb****3****Sn: Internal Sn-Rod OI-ST ASC2002**

**Nb****3****Sn: Internal Sn, ITER type low hysteresis loss design**

**(IGC - Gregory et al.) [Non-Cu *****J*****c****]**

**Nb****3****Sn: Bronze route int. stab. -VAC-HP, non-(Cu+Ta) *****J*****c****,**

**Thoener et al., Erice '96.**

**Nb****3****Sn: Bronze route VAC  62000 filament, non-Cu 0.1μohm-m**

**1.8 K *****J*****c****, VAC/NHMFL data courtesy M. Thoener.**

**Nb****3****Sn: SMI-PIT, non-Cu *****J*****c****, 10 μV/m, 192 filament 1 mm dia.**

**(45.3% Cu), U-Twente data provided March 2000**

**Nb****3****Sn: Tape (Nb,Ta)****6****Sn****5****+Nb-4at.%Ta core, [*****J*****ccore****, core ~25 %**

**of non-Cu] Tachikawa et al. '99**

**Nb****3****Al: Nb stabilized 2-stage JR process (Hitachi,TML-NRIM,**
**IMR-TU), Fukuda et al. ICMC/ICEC '96**

**Nb****3****Al: 84 Fil. RHQT Nb/Al-Ge(1.5μm), Iijima et al. NRIM**

**ASC'98 Paper MVC-04**

**Nb****3****Al: RQHT+2 At.% Cu, 0.4m/s (Iijima et al 2002)**

**Nb****3****Al: JAERI strand for ITER TF coil**

**Bi-2212: non-Ag *****J*****c****, 427 fil. round wire, Ag/SC=3 (Hasegawa**
**MT17 2000).**

**Bi 2223: Rolled 85 Fil. Tape (AmSC) B||, UW'6/96**

**Bi 2223: Rolled 85 Fil. Tape (AmSC) B|_, UW'6/96**

**PbSnMo****6****S****8**** (Chevrel Phase):  Wire in 14 turn coil, 4.2 K, 1**

**μVolt/cm, Cheggour et al., JAP 1997**

**MgB****2****: 10%-wt SiC doped (Dou et al APL 2002, UW**

**measurements)**

**Nb**

**3**

**Al **

**RQHT+2At%Cu**

**Nb**

**3**

**Sn**

**Bronze**

**At 4.2 K Unless**

**Otherwise Stated**

**1.8 K**

**Nb-Ti-Ta**

**PbSnMo**

**6**

**S**

**8**

**1.8 K**

**Nb-Ti**

**Nb**

**3**

**Sn Tape**

**from (Nb,Ta)**

**6**

**Sn**

**5**

**Nb**

**3**

**Sn**

**1.8 K Bronze**

**Nb**

**3**

**Sn**

** ****Internal Sn**

**2212 **

**Round Wire**

**MgB**

**2**

**SiC**

**Nb**

**3**

**Sn**

** ****PIT**

**Nb**

**3**

**Al **

**2 stage JR**

## High Field Superconductors

- Bi2212
- Highest Critical Currents above 14 T
- Flat Jc vs B
- Nb3Al
- High Strength
- High Critical Current Densities possible
- MgB2
- Only 2 years old, HTS is now a venerable 17 years!
- Very low cost raw materials, Ag not required.
- With improved *H*c2 provides both temperature and field margin.

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Bi-2212 round wire has been cabled for accelerator magnets. 

*J*c(12 T, 4.2 K, non-silver) > 2000 A/mm2 in new material.
- Long lengths( > 1500 m) are being produced.
*J*c vs strain for Rutherford cables looks promising (LBNL results).
- React/wind (BNL) and Wind/react (LBNL) coils are being made.

- Cable made at LBNL
- From Showa strand

**Ron Scanlan (LBNL) ASC2002**

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## MgB2: first 2-gap superconductor

- MgB2: first 2-gap superconductor

*Choi et al., *
*Nature ****418**** (2002) 758*

- Fermi surface from **out-of-plane**-bonding states of B *p*z orbitals:
-  **********(4.2K) ******** 2.3 meV**
-  **small gap**

- Fermi surface from **in-plane** -bonding states of B *p*xy orbitals:
**********(4.2K) ******** 7.1 meV**
**large gap**

*V. Braccini et al. APS2003, Gurevich et al Nature*
*University of Wisconsin-Madison*

## MgB2: There Are Mechanisms for increasing Hc2

**3 impurity scattering channels**

- Increase Hc2 by:
- Increasing 
***Selective doping of ************ and ************ bands***

** ****Intraband **scattering within each  and  sheet
** ****Interband** scattering

*H*c2 is strongly enhanced as compared to the one-band WHH extrapolation 		***H*****c2****(0) > 0.7 *****T*****c *****H*****/****c2****(*****T*****c****) **

- by substitutions for B

- by substitutions for Mg

- MgB2: There Are Mechanisms for increasing *H*c2

## Bulk: Resistivity enhancement after Mg exposure .....

**RRR**:    **15****                 3**
******(40K)**: **1**** ******** ****cm****         ****18**** ******** ****cm [B]**
**	****	****        ****14**** ******** ****cm [C]**
** **

- Bulk: Resistivity enhancement after Mg exposure .....

- 0.0

- 0.2

- 0.4

- 0.6

- 0.8

- 1.0

- 0

- 100

- 200

- 300

**Temperature [K]**

****

**/**

****

**(300K)**

**(C) Quenched**

**(B) Slow cooled**

**(A) Original**

- 0.5

- 1.0

- 35

- 36

- 37

- 38

- 39

- 40

**T [K]**

****

**(40K)**

-       0

**B**

**A**

**C**

**T****c**: **39 K**

**36.5 K  [B]**
**37 K  [C]**

*V. Braccini et al. APL 2002 UW-ASC*

## ... enhancement of Hc2

- 0

- 5

- 10

- 15

- 20

- 5

- 10

- 15

- 20

- 25

- 30

- 35

- 40

**T (K)**

****

** ****(**

****

** ****cm)**

- 0

- 3

- 6

- 9

- 12

- 15

- 5

- 10

- 15

- 20

- 25

- 30

- 35

- 40

**T (K)**

****

** ****(**

****

**cm)**

- 0.0

- 0.5

- 1.0

- 1.5

- 5

- 10

- 15

- 20

- 25

- 30

- 35

- 40

**T (K)**

****

** ****(**

****

**cm)**

**A**

- 0T

**C**

***H******c2***

**B**

- 9T

**0.5****     ****1.2**

**37K**         **39K**

- 0

- 2

- 4

- 6

- 8

- 10

- 15

- 20

- 25

- 30

- 35

- 40

**Temperature (K)**

**Upper critical field (T)**

- dHc2/dT:

- :

**1    ****        ****18**

- (T/K)

- cm

*V. Braccini et al. APL 2002 UW-ASC*

## Upper critical field depends very strongly on 

**A**

**B**

**B aged**

- Upper critical field depends very strongly on 

- 33T resistive magnet at the NHMFL in Tallahassee, FL

|  | Tc,K | cm | RR | dHc2/dT |
| --- | --- | --- | --- | --- |
| A | 39 | 1 | 15 | 0.5 |
| B | 37 | 18 | 3 | 1.2 |
| Ba | 38 | 5 | 5 | 1 |

*V. Braccini et al. APS2003*

- Untexured bulk samples suggest that MgB2 is capable of >30 T at 4.2 K and >10 T at 20 K.

## MgB2: Enhancement Summary-Films

*H*c2 34 T, *H*c2// **49** T (dirty film)
*H*c2 29 T (untextured polycrystalline bulk)
-  Systematic changes in , *T*c, *H*c2 in bulk and thin films
-  2-band physics

*MgB**2**: Enhancement Summary-Films*

*Gurevich et al (Nature) . . Etc. UW-Madison*

*Thin films show that MgB**2** is capable of higher H**c2** than even Nb**3**Sn.*

*Wire expectation*

## So Why Nb3Sn?

- Increasing Critical Current Density at Field Range for next generation of magnets.
- Production Experience
- Strand production
- Cable production
- Sub-scale dipole magnets
- ITER CS Model Coil
- Multiple Vendors
- Cu Stabilizer
- And $$$$$$$€€€€€€€¥¥¥¥¥¥¥

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Ron Scanlan (LBNL): ASC2002$/kA-m improvements mostly through Jc improvements:

**ITER**

**D20**

**RD-3**

**HD-1**

**KSTAR**

***Further cost improvements must come through process scale-up***

## Industrial Nb3Sn Fabrication Processes

- The bronze process continues to have a market for NMR where high *n*-value is important. High Cu:Sn ratios means *J*c limited.
- PIT produces deff=dfil and can produce high *J*c but is expensive and is only commercially available from one manufacturer.
- Internal Sn: Both Rod and MJR can produce 2900 A/mm2 12 T, 4.2 K. Large deff in high *J*c strands.

**NbSn**

**2**

** ****+ Cu +Sn**

**Powder**

**Nb**

- Cu

*Bronze Process*

*PIT – Powder in Tube*

*Internal Sn (**Rod Process Shown**)*

## Overview of Nb3Sn Types

**ITER: Distributed Filaments. ****Large Cu sink for Sn. Variable and low Sn composition in A15**

**“****High *****J*****c****”**
**Low Cu, high Sn content in A15 and high homogeneity. Large or coalesced filaments.**

## Where is the Jc coming from?

**Where is the J****c**** coming from?**

**0**

**2000**

**4000**

**6000**

**8000**

**10000**

**12000**

**7**

**8**

**9**

**10**

**11**

**12**

**13**

**14**

**15**

**16**

**Applied Field, T**

**Layer Critical Current Density, A/mm2  **

**High Jc Internal Sn IGC EP2-1-3-2 700°C HT**

**High Jc Internal Sn: ORe110(695/96)**

**SMI-PIT Nb-Ta Tube: 64 hrs@675 °C-small grains**

**High Jc Internal Sn MJR TWC1912**

**504 Filament SMI-PIT, small grains only**

**ITER: Mitsubishi Internal Sn**

**ITER: LMI Internal Sn**

**ITER: Furukawa Bronze Process**

**ITER: VAC 7.5% Ta Bronze Process**

**ITER low loss**

**“****high J****c****”**

**22-24 At.% Sn in A15, equiaxed to columnar transition**

**23-24.5 At.% Sn in A15, equiaxed grains uniform across layer**

***“******High J******c******” strand has ******much less Cu****** (more hysteresis loss) and more Sn and Nb. High Sn levels maintained throughout reaction***

***Layer J******c****** for low-loss ITER-style strand quite different to high J******c****** strand.***

**Nb****3****Sn**

## Composition, Tc and Hc2 effects in Nb3Sn

***Devantay et al. J. Mat. Sci.*****, 16, 2145 (1981)**

*Charlesworth et al. J. Mat. Sci.*, **5**, 580 (1970)

***Data compiled  by Devred from original data assembled by Flukiger, Adv. Cryo. Eng., ******32, 925 (1985)****** ***

- Sn, *T*c and *H*c2 gradients!
- Nb3Sn is seldom Nb-25at%Sn

**Composition, T****c**** and H****c2**** effects in Nb****3****Sn**

## “High Jc” in Internal Sn is achieved by reducing the Cu between the filaments to a minimum while maintaining Sn levels 

*Outokumpu Advanced Superconductors (OAS) DOE-HEP CDP program reported by Ron Scanlan at ASC2002** *

- A15 % in OI-ST MJR Sub-elements at 60% in the 2200 A/mm2 strand
- Note the 10% variation through Sn redistribution during HT

**MJR can reach ~10:1 Nb:Cu in Filament pack. RIT ~ 4:1**

## “High Jc” A15 – Thick layers, shallow composition gradient, high Sn, low Cu (2200 A/mm2, 12 T, 4.2 K)

**A15**

**Nb barrier**

**Void**

**Sn Diffusion**

**Cu**

**Cu**

**Cu(Sn)**

**Nb****3****Sn**

## Columnar are markers for local Sn deficiency

***Columnar A15 growth is observed when Sn supply is diminished***
***Increased aspect ratio can be used to indicate reduced Sn in the A15***
***Using this method the local A15 inhomogeneity can be implied on a sub-micron scale.***

**P. J. Lee, C. M. Fischer, M. T. Naus, A. A. Squitieri, D. C. Larbalestier, "The Microstructure and Microchemistry of High Critical Current Nb3Sn Strands Manufactured by the Bronze, Internal-Sn and PIT Techniques," Applied Superconductivity Conference , 2002.  http://128.104.186.21/asc/pdf_papers/760.pdf**

## In low-Cu “high Jc” strand – Nb dissolution

**Nb dissolution causes loss in contiguous A15 area.**
**Breach of the barriers by Sn enables LBNL SC group to control RRR by HT**

## OI-ST MJR Very High Jc: 2900 A/mm2, 12 T

- MJR (ORe137): <15 volume % Cu in sub-element
- Significant excess Sn even including barrier
- The Sn core is larger than required to react all Nb and Nb(Ti) and form stoichiometric Nb3Sn

*Mike Naus (LTSW ’01) and PhD thesis 2002 shows important role of Sn:Nb in determining T**c** and H**c2: http://128.104.186.21/asc/pdf_papers/theses/mtn02phd.pdf*

## Mike Naus: Universal Plot of Goodness

***Mike Naus: LTSW 2001***

*Remarkably this plot includes non-alloyed, Ta and Ti alloyed Nb**3**Sn*

**http://128.104.186.21/asc/pdf_papers/theses/mtn02phd.pdf**

## 2900 A/mm2 in OI-ST: also in RRP*

**2900 A/mm2 in OI-ST: also in RRP***

- Nb-Ta alloy rod stack
- More Cu remains between filaments than in MJR
- Sub-elements *very* close together
- Barrier breached and external A15 formed
- RRR control feature?!
- Some dissolution of Nb into core.
- *1000m lengths available.
- *(this note added in postcript
-  thanks to Ron Scanlan – LBNL).

***RRP=Rod Restack**
**Process**

## 2900 A/mm2 in OI-ST RRP

**Nb barrier**

**A15**

**Cu(Sn) Core**

**Stabilizer Cu**

**Cu(Sn)**

**Void**

- FESEM-BEI image showing barrier, sub-element spacing and Nb dissolution

## Sub-element uniformity: very good

- Sub-element cross-sectional areas:
- Coefficient of variation 2.7% - equivalent to good SSC Nb-Ti strand
- Compares to 1.1-2.2 % for SMI-PIT B34 Filaments
- 0.8 % for Edge Strengthened B134 Filament
- But sub-elements are still too-large (~100μm) and the barriers too thin.

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Microchemistry: Center of A15 layer

- RRP 6445 2900 A/mm2 HT and *J*c by OI-ST *(Kramer extrapolation)*
- Nb(Ta): **25.0** Atomic % Sn (Ignoring 1.4 At.% Cu signal)
- 2900 A/mm2 + Confirmed in transport by OI-ST in RRP6555-A, 0.8mm
- SMI-PIT B134 80hrs at 675 °C, *J*c (non-Cu) 1961 A/mm2 12 T
**24.0** Atomic % Sn (Ignoring 1.2 At. % Cu Signal)
- SMI-PIT B34 64hrs at 675 °C, *J*c (non-Cu) 2250 A/mm2 12 T
**24.1** Atomic % Sn (Ignoring 2.0 At. % Cu Signal)

- Conditions:	FESEM EDS Analysis
- 		Same session, fresh calibration, 20 kV
- 		1 sigma Sn error <0.22 Atomic %
*PIT J*c data:	All measured by transport by UW

## OI-ST 2900 A/mm2 Strand: New Jcsc

**OI-ST RRP**
**2900 A/mm2**
**(12T, 4.2K)**

- Non-Cu:A15 ratio from image analysis of high resolution FESEM images of 4 sub-elements

- 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Ta alloy rod produces larger grains

**ORe110**
**Ti alloy MJR**

**OI-ST**
**Ta alloy RRP**

## Ta alloy rod produces larger grains

**ORe110**
**Ti alloy MJR**

**OI-ST**
**Ta alloy RRP**

**(d*~180 nm)**

**(d*~140 nm)**

## A layer of large A15 grains surrounds the core – starting to look like PIT

**A layer of large A15 grains surrounds the core – starting to look like PIT**

- RRP: Outer row, outer layer

**Some morphology associated with original rods**

## Thus the Qgb must be higher . . . 

**OI-ST RRP**
**2900 A/mm2**
**(12T, 4.2K)**

- Grain Boundary Density from IA of *ONE* fracture image!

- We calculate the specific boundary pinning force, *Q**GB*, using Kramer’s formalism:
-            *Q**GB**=F**p**/****S**gb*
- where ** is an efficiency factor which accounts for the proportion of the grain boundary that is oriented for pinning. We apply a value of 0.5 for **, a value previously used for columnar grains

## Fp Very High for “High Jc” Nb3Sn

**1**

**10**

**100**

**0**

**5**

**10**

**15**

**20**

**25**

**Applied Field (T)**

**Bulk Pinning Force, **

***F***

**p**

** ****(GN/m3)**

**Nb-Ti:  APC strand Nb-47wt.%Ti with**

**24vol.%Nb pins (24nm nominal diam.) -**

**Heussner et al. (UW-ASC)**

**Nb-Ti: Best Heat Treated UW Mono-**

**Filament. (Li and Larbalestier, '87)**

**Nb-Ti: Nb-Ti/Nb (21/6) 390 nm multilayer**

**'95 (5°), 50 μV/cm, McCambridge et al.**

**(Yale)**

**Nb****3****Sn: Sn plated Cu APC, 40 hr@650**

**°C, R. Zhou PhD Thesis (OST), '94**

**Nb****3****Sn: Mitsubishi ITER BM3 Internal**

**Sn**

**Nb****3****Sn Strand: High *****J*****c**** Internal Sn RRP**

**(Parrell et al ASC'02)**

**Nb****3****Al: Transformed rod-in-tube Nb****3****Al**

**(Hitachi,TML-NRIM), Nb Stabilized - non-**

**Nb *****J*****c****, APL, vol. 71(1), pp.122-124), 1997**

**NbN: 13 nmNbN/2 nmAlN multi-layer || B,**

**Gray et al. (ANL) Physica C, 152 '88**

**YBCO: /Ni/YSZ ~1 μm thick**

**microbridge, H||ab 75 K, Foltyn et al.**

**(LANL) '96**

**Bi-2212:  19 filament tape B||tape face -**

**Okada et al (Hitachi) '95**

**Bi 2223: Rolled 85 Fil. Tape (AmSC) B||,**

**UW'6/96**

**MgB****2****: 10%-wt SiC doped (Dou et al**

**APL 2002, UW measurements)**

**Nb-Ti**

**MultiLayer**

**APC Nb-Ti**

**Nb**

**3**

**Sn**

**Cu plated APC**

**2223**

**Tape B||**

**2212 Tape**

**MgB**

**2**

**SiC**

**Nb**

**3**

**Sn**

**ITER**

**Nb**

**3**

**Sn Internal Sn**

**"High **

***J***

**c**

**"**

**Nb**

**3**

**Al RIT**

** ****HT Nb-Ti**

**NbN**

## High Jc Internal Sn (twisted): 0.5% Bend Strain

**Tensile**

**Compressive**

**Barrier**

**Cu**

**Nb****3****Sn**

**Nb****3****Sn is susceptible to filament breakage under small bend strains ~0.5%**
**If the Nb****3****Sn layer us continuous (as in the prototype IGC-AS strand) breakage spans the entire tensile side.**

## PIT geometry leaves thick unreacted Nb and corners of hexagonal filaments.

***After HT*****: Weakly bonded porous core left inside A15**

*SMI-PIT filaments are otherwise remarkably homogeneous in area cross-section*

***Before HT*****: Homogeneous stack of powder in Nb tubes**

***Commercial PIT strand is manufactured by Shapemetal Innovation BV, the Netherlands. This process was originally developed by ECN and is termed the ECN process.***

## Very high Sn levels can be achieved at elevated temperatures: PIT(Ta): SMI 34 64hrs@800C

**Nb(Ta)**

**A15**

**Core**

- * = ignoring Cu

- 25.20 (±0.1) At.%Sn*

- 24.8 (±0.2) At.%Sn*

- 24.5 (±0.3) At.%Sn*

***Very large grain sizes, however, result in low J******c***

## Powder-in-tube Nb(Ta): Twisted, 0.5% bend

- No cracking seen at 0.5% strain (eventually cracks at 0.6%)
- Although the Nb layer reduces the efficiency of the non-Cu package it applies more precompression to the A15

- Matthew C. Jewell, Peter J. Lee and David C. Larbalestier, "The Influence of Nb3Sn Strand Geometry on Filament Breakage under Bend Strain as Revealed by Metallography", Submitted at the 2nd Workshop on Mechano-Electromagnetic Property of Composite Super-conductors, for publication in Superconductor Science and Technology (SuST), March 3rd 2003. _[http://www.](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[cae](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[.wisc.edu/%7Eplee/pubs/](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[pjl](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[-](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[mcj](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[-mem03-](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[sust](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[.](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[pdf](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)_

## Summary: Recent UW Nb3Sn Results

- Remarkable improvements in the critical current densities (layer and non-Cu) of Nb3Sn have been observed in Nb3Sn strand fabricated by the PIT and Internal Sn process.
- Grain Size of this Ta-alloyed conductor is small enough to yield high *J*c but is larger (d*~180 nm) than found in Nb(Ti) MJR (d*~140 nm).
- Remarkably high *Q*gb suggests that the grain boundary chemistry is different.
- If Nb(Ta)3Sn grain size can be reduced without sacrificing stoichiometry further advances should be possible.
- Effective filament diameter is 30 (PIT) -100 μm (Internal Sn) and needs to be improved.
- PIT bend results suggest better strain tolerance could be achieved

- Lee: 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Accelerator Conductor Issues

- Can the effective filament size for “High *J*c” Nb3Sn strand be reduced.
- Can the cost of PIT strand be reduced?
- Can the cost of all the other Nb3Sn strands be reduced?
- Are we close to the limit for Nb3Sn strand *J*c?
- Can we engineer enough “Stress Relief” for Nb3Sn
- Can Nb3Al be made in long lengths at low cost?
- Will MgB2 continue to make gains, should it be supported?
- Can the high *T*c be exploited?

- Lee: 1st Workshop on Advanced Accelerator Magnets, Archamps, France, March 17 and 18, 2003

## Bibliography

- M. T. Naus, "Optimization of Internal-Sn Nb3Sn Composites," Ph.D. Thesis, Materials Science Program, University of Wisconsin-Madison, 2002. _[http://128.104.186.21/asc/pdf_papers/theses/mtn02phd.](http://128.104.186.21/asc/pdf_papers/theses/mtn02phd.pdf)__[pdf](http://128.104.186.21/asc/pdf_papers/theses/mtn02phd.pdf)_
- P. J. Lee, C. M. Fischer, M. T. Naus, A. A. Squitieri, D. C. Larbalestier, "The Microstructure and Microchemistry of High Critical Current Nb3Sn Strands Manufactured by the Bronze, Internal-Sn and PIT Techniques," Applied Superconductivity Conference , 2002. _[http://128.104.186.21/asc/pdf_papers/760.pdf](http://128.104.186.21/asc/pdf_papers/760.pdf)_
- M. T. Naus, M. C. Jewell, P. J. Lee, D. C. Larbalestier, "Lack of Influence of the Cu-Sn Mixing Heat Treatments on the Super-Conducting Properties of Two High-Nb, Internal-Sn Nb3Sn Conductors," CEC-ICMC Advances in Cryogenic Engineering, 48[B], 1016-1022, 2002. _[http://128.104.186.21/asc/pdf_papers/698.](http://128.104.186.21/asc/pdf_papers/698.pdf)__[pdf](http://128.104.186.21/asc/pdf_papers/698.pdf)_
- C. M. Fischer, "Investigation of the Relationships Between Superconducting Properties and Nb3Sn Reaction Conditions in Powder-in-Tube Nb3Sn Conductors," M.S. Thesis, Materials Science Program, University of Wisconsin-Madison, 2002. _[http://128.104.186.21/asc/pdf_papers/theses/cmf02msc.pdf](http://128.104.186.21/asc/pdf_papers/theses/cmf02msc.pdf)_
- C. M. Fischer, P. J. Lee, D. C. Larbalestier, "Irreversibility Field and Critical Current Density as a Function of Heat Treatment Time and Temperature for a Pure Niobium Powder-in-Tube Nb3Sn Conductor," CEC-ICMC Advances in Cryogenic Engineering, 48[B], 1008-1015, 2002. _[http://128.104.186.21/asc/pdf_papers/704.pdf](http://128.104.186.21/asc/pdf_papers/704.pdf)_
- P. J. Lee, C. D. Hawes, M. T. Naus, A. A. Squitieri, D. C. Larbalestier, Compositional and Microstructural Profiles across Nb3Sn Filaments", IEEE Transactions on Applied Superconductivity, 11(1), pp. 3671-3674, 2001. _[http://128.104.186.21/asc/pdf_papers/662.](http://128.104.186.21/asc/pdf_papers/662.pdf)__[pdf](http://128.104.186.21/asc/pdf_papers/662.pdf)_
- Matthew C. Jewell, Peter J. Lee and David C. Larbalestier, "The Influence of Nb3Sn Strand Geometry on Filament Breakage under Bend Strain as Revealed by Metallography", Submitted at the 2nd Workshop on Mechano-Electromagnetic Property of Composite Super-conductors, for publication in Superconductor Science and Technology (SuST), March 3rd 2003. _[http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)__[pdf](http://www.cae.wisc.edu/%7Eplee/pubs/pjl-mcj-mem03-sust.pdf)_
- R. M. Scanlan, “Conductor development for high energy physics-plans and status of the US program,”, IEEE Transactions on Applied Superconductivity, 11(1) , pp: 2150 –2155, Mar 2001. _[http://ieeexplore.ieee.org/iel5/77/19887/00920283.pdf?isNumber=19887&prod=IEEE+JNL&arnumber=920283&arSt=2150&ared=2155&arAuthor=Scanlan%2C+R.M.%3B](http://ieeexplore.ieee.org/iel5/77/19887/00920283.pdf?isNumber=19887&prod=IEEE+JNL&arnumber=920283&arSt=2150&ared=2155&arAuthor=Scanlan%2C+R.M.%3B)_
- R. M. Scanlan, D. R. Dietderich, Progress and Plans for the U. S. HEP Conductor Development Program, ASC2002 presentation 5LA04.
- V. Braccini, L. D. Cooley, S. Patnaik, P. Manfrinetti, A. Palenzona, A. S. Siri, D. C. Larbalestier, "Significant Enhancement of Irreversibility Field in Clean-Limit Bulk MgB2," APL, 9 Dec. 2002; 81(24): 4577-9. _[http://arxiv.org/ftp/cond-mat/papers/0208/0208054.pdf](http://arxiv.org/ftp/cond-mat/papers/0208/0208054.pdf)_

## Acknowledgments

- Ron Scanlan (LBNL): Who leads the US-DOE HEP Conductor Development Program supplied additional slides.
- Jeff Parrell, Mike Field and Seung Hong at OI-ST have advanced the properties of Nb3Sn at a remarkable rate and have provided strand samples to both Labs and Universities.
- Tae Pyon and Eric Gregory (now with Accelerator Technology Corp) of IGC-AS (now Outokumpu Advanced Superconductors) supplied additional internal Sn strands for these studies.
- Jan Lindenhovius of Shapemetal Innovation BV, supplied the UW with PIT strand for these studies.
- Mike Naus and Chad Fischer (now with Intel) provided much of the internal Sn and PIT (respectively) data presented here as graduate students at the University of Wisconsin-Madison