Impact of Sample Preparation Procedure on the Test Results of Four US ITER TF Conductors

In the scope of the qualification tests of the ITER TF conductors, four samples for the SULTAN facility have been prepared, each consisting of two conductor sections manufactured by the US ITER Domestic Agency. The samples are nicknamed USTF1, USTF2, USTF3 and USTF4. The conductor sections used for USTF1 and USTF3, as well as those for USTF2 and USTF4, are identical. The conductor terminations for the samples USTF1 and USTF4 are prepared by the "solder filling" method, where a copper sleeve is swaged on the dismantled conductor before the heat treatment, and the cable space is filled with a soldering alloy by siphon after the heat treatment. In USTF2 and USTF3, the conductor terminations are dismantled after the heat treatment, and the cable ends are dipped into a bath of molten solder. The main test of the conductor characterization in SULTAN is the current sharing temperature (T_cs) test at 10.78 T background field. The current is raised up to 68 kA current in steps of 10 kA. Then, the coolant temperature is raised in steps of 0.25 K till quench occurs. Early voltage is observed during the current ramp before heating even at relatively low current. Due to the broad voltage-temperature (V-T) transition, the early voltage causes an uncertainty in the assessment of the conductor performance. The comparison of the test result of USTF1 vs. USTF3 and USTF2 vs. USTF4 enables to clarify the impact of the termination preparation procedure on the early voltage. In the case the early voltage is caused by non-uniform current distribution and high inter-strand resistance at the joints, the V-T behavior should be clearly different. In this paper, the joint preparation procedures are described, and the impact of the joint preparation on the conductor performance is discussed.