VAMAS intercomparison of critical current measurement in Nb/sub 3/Sn wires

Tachikawa, K.; Itoh, K.; Wada, Hitoshi; Gould, Daniel; Jones, H.; Walters, C.R.; Goodrich, Loren F.; Ekin, John W.; Bray, S L.

doi:10.1109/20.92784

Cited by 16 publications

(3 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The history of interlaboratory comparisons of measurements on superconductors tells us that careful measurement methods are needed to obtain consistent results [1][2][3][4][5][6][7][8][9][10]. Inconsistent results can lead to many problems including: a mistrust of the results of others, unfair advantages in commerce, and erroneous feedback in the optimization of conductor performance.…”

Section: Introductionmentioning

confidence: 99%

Final Technical Report

Goodrich¹

2011

View full text Add to dashboard Cite

Section: Introductionmentioning

confidence: 99%

Final Technical Report

Goodrich¹

2011

View full text Add to dashboard Cite

“…Although the thermal contraction of barrel material is known, that of the present high-strand is not. Composites like the wire used for VAMAS comparative measurements [2] typically had a contraction of 0.28% for a bronze process wire and 0.26% for an internal-Sn processed wire [3]. Table I lists the average contraction of barrel materials and that of superconductor, not the composite [4]- [6].…”

Section: Introductionmentioning

confidence: 99%

Effect of Barrel Material on Critical Current Measurements of High-${\rm J}_{\rm c}$ RRP ${\rm Nb}_{3}{\rm Sn}$ Wires

Ghosh

2011

IEEE Trans. Appl. Supercond.

View full text Add to dashboard Cite

strands extracted from a 20-strand rectangular Rutherford cable were reacted on either stainless steel or Ti-alloy barrels and the critical current, , in the field range of 8-11.5 T was measured on ITER-type barrels made from Ti-6Al-4V alloy, 304 stainless steel and G-10. Measurements on the "standard" Ti-alloy barrel using the test procedure employed at BNL are shown to reproduce for extracted strands to 2%. The data for the sample mounted on the "standard" Ti-alloy are fit to the deviatoric strain scaling model developed for by the University of Twente group using an arbitrary pre-strain. Using the parameters for this fit, the data for the other barrels are fitted by only adjusting the strain. Using this procedure, the strain difference due to the barrel material is determined. Assuming a thermal pre-strain of 0.2% for the sample measured on the Ti-alloy barrel, the use of stainless steel barrel increases the compressive strain by 0.07%, that of G-10 by 0.10%. With the wire soldered to the stainless steel barrel, the strain increases to 0.15%. Details of this study are presented.

show abstract

“…The superconductor community has learned that careful measurement methods are needed to obtain consistent results on superconductors because subtle differences in methods can lead to unacceptable measurement biases. Two key international inter-laboratory comparisons of I c measurements with the sample in liquid helium have been conducted by Versailles Project on Advanced Materials and Standards (VAMAS) [ 5 – 7 ]. In the first comparison, the coefficients of variation were 8.0 and 20.6 % for I c and n -value, respectively, on a Nb 3 Sn sample at 12 T. The most significant influence quantity in the first comparison was the strain state of the sample.…”

Section: Introductionmentioning

confidence: 99%

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors

Goodrich¹,

Cheggour²,

Stauffer³

et al. 2013

J. RES. NATL. INST. STAN.

Self Cite

View full text Add to dashboard Cite

We review variable-temperature, transport critical-current (Ic) measurements made on commercial superconductors over a range of critical currents from less than 0.1 A to about 1 kA. We have developed and used a number of systems to make these measurements over the last 15 years. Two exemplary variable-temperature systems with coil sample geometries will be described: a probe that is only variable-temperature and a probe that is variable-temperature and variable-strain. The most significant challenge for these measurements is temperature stability, since large amounts of heat can be generated by the flow of high current through the resistive sample fixture. Therefore, a significant portion of this review is focused on the reduction of temperature errors to less than ±0.05 K in such measurements. A key feature of our system is a pre-regulator that converts a flow of liquid helium to gas and heats the gas to a temperature close to the target sample temperature. The pre-regulator is not in close proximity to the sample and it is controlled independently of the sample temperature. This allows us to independently control the total cooling power, and thereby fine tune the sample cooling power at any sample temperature. The same general temperature-control philosophy is used in all of our variable-temperature systems, but the addition of another variable, such as strain, forces compromises in design and results in some differences in operation and protocol. These aspects are analyzed to assess the extent to which the protocols for our systems might be generalized to other systems at other laboratories. Our approach to variable-temperature measurements is also placed in the general context of measurement-system design, and the perceived advantages and disadvantages of design choices are presented. To verify the accuracy of the variable-temperature measurements, we compared critical-current values obtained on a specimen immersed in liquid helium (“liquid” or Ic liq) at 5 K to those measured on the same specimen in flowing helium gas (“gas” or Ic gas) at the same temperature. These comparisons indicate the temperature control is effective over the superconducting wire length between the voltage taps, and this condition is valid for all types of sample investigated, including Nb-Ti, Nb3Sn, and MgB2 wires. The liquid/gas comparisons are used to study the variable-temperature measurement protocol that was necessary to obtain the “correct” critical current, which was assumed to be the Ic liq. We also calibrated the magnetoresistance effect of resistive thermometers for temperatures from 4 K to 35 K and magnetic fields from 0 T to 16 T. This calibration reduces systematic errors in the variable-temperature data, but it does not affect the liquid/gas comparison since the same thermometers are used in both cases.

show abstract

VAMAS intercomparison of critical current measurement in Nb/sub 3/Sn wires

Cited by 16 publications

References 1 publication

Final Technical Report

Final Technical Report

Effect of Barrel Material on Critical Current Measurements of High-${\rm J}_{\rm c}$ RRP ${\rm Nb}_{3}{\rm Sn}$ Wires

Kiloampere, Variable-Temperature, Critical-Current Measurements of High-Field Superconductors

Contact Info

Product

Resources

About