Comparative Measurements of ITER Nb₃Sn Strands Between Two Laboratories

Abstract

ITER Nb3Sn strand quality verification tests require large quantities of precise measurements. Therefore regular cross-checking between testing laboratories is critically important. In this paper, we present results from a cross-checking test of 140 samples between the National High Magnetic Field Laboratory, USA and the University of Twente, the Netherlands. The tests comprise measurements at 4.2 K on critical current, RRR and hysteresis loss, while at room temperature the chromium layer thickness, Cu/nonCu ratio, filament twist pitch, and diameter were determined. Our results show very good agreement between the two labs. The reasons for small random discrepancies are discussed.

Influence of heat treatment excursion on critical current and residual resistivity ratio of ITER Nb3Sn strands

“…Figures 3(a) and (b) show 12 T I c versus heat treatment temperatures for the JASTEC and KAT samples respectively. Evidently I c is not sensitive to heat treatment temperature or time within the experimental uncertainty which can be up to 5% of I c [25]. When the heat treatment time in step two is reduced to 20 h or less, however, I c of the JASTEC strand reduces significantly as shown in figure 4(a) where data can be fitted (solid line) using an exponential function…”

Verification Testing of MQXFA Nb3Sn Wires Procured Under LARP

“…Straight wires approximately 25 cm long were inserted into 1 mm interior diameter quartz tubes to create RRR samples. The ends of the Nb 3 Sn wire for both the I c and RRR samples were welded shut using a spot welder to prevent tin leak during the heat treatment [3], [4]. Groups of samples were wrapped in stainless steel foil before being placed in the center of the furnaces.…”

“…The set up used for RRR measurements was the same as previously reported [3], [4]. Unlike for the ITER project, which defined RRR as the ratio of resistances at 273 K and 20 K, the LARP specification called for the use of the IEC standard [5], which is defined as the ratio of resistance at room temperature (295 K) to that determined by the intersection of two straight lines extrapolated from the resistance versus temperature curve, as shown on Fig.…”