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

Abstract

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.

A review of conductor performance for the LARP high-gradient quadrupole magnets

“…BNL samples are reacted on a stainless steel 304 reaction holder, and the strands are then transferred to a Ti-6Al-4V measurement holder after reaction and soldered to copper rings that are permanently connected to the measurement holder, thereby addressing some of the disadvantages of the standard ITER method [19,20]. The witness samples for LBNL are reacted on the measurement holder using a recently proposed new system for high-current superconducting wires [21], which removes the post-reaction handling of the wires, while retaining the possibility to measure modern high-current wires, which is complicated, if not impossible, using the standard ITER method that was developed for medium-current wires.…”

“…The typical axial strain state for the Nb 3 Sn in a free wire after cool down to 4.2 K is of order −0.3 to −0.35%. Since a Nb 3 Sn composite wire will typically contract more than a Ti-6Al-4V ITER barrel, the wire will be slightly stretched during cool down on an ITER barrel [19,20]. To scale the eventual fit parameters to more realistic values, a generic compressive strain state = −0.2% is assumed for both the wire and for the conductor in the coil throughout the analysis in this paper.…”

Superconducting Properties of Titanium Alloys (Ti-64 and Ti-6242) for Critical Current Barrels

“…The excellent mechanical properties and good machinability of this material make it the material of choice for barrels [5]. It is a highly resistive material with low thermal conductivity which has a thermal contraction similar to Nb3Sn to minimize prestraining of the strands [6]. The high electrical resistivity of Ti-64 at cryogenic temperatures is due to the high Ti content in solid solution [7].…”

Effective Low Magnetic Field Jc(B) Scaling of ITER Nb3Sn Strands by Magnetization and Critical Current Measurements

“…Besides the magnetic field and temperature, the critical current density of the Nb 3 Sn superconductor is strongly dependent on the strain applied to the material [14], [15]. The Nb 3 Sn composite wire will contract under axial strain after cooling down to 4.2 K and typically contract more in comparison to a Ti6Al4V ITER barrel; it means that the wire will be slightly stretched during cool down on an ITER barrel [16], [17]. Furthermore, the strain stays within a narrow ranging window, and the average values of BR and IT strands are −0.19 and −0.13%, respectively [18].…”