Abstract-A joint in the superconductor and stabilizer is added to the ETM conductor in the POPE. The joint design is similar to that proposed by Westinghouse for the SMES ETM field joints.Fabrication of the joint is described. Measurements on the performance of the superconducting joint operated in subcooled He II and of the stabilizer joint at 14 K are reported. Measured superconductor joint resistance is 1.6 n o , which agrees with previous analytic calculations. The stabilizer joint RR matches the conductor stabilizer RR. The joint met or exceeded all operational requirements throughout the experiment demonstrating its reliability and small joule heating
L INTRODUCTIONThe test coil for the POPE (Proof of Principle Experiment) is three one meter diameter turns of conductor consisting of eight Cu/NbA'i superconducting strands soldered into grooves in the 2.54 cm diameter high purity aluminum (€PAL,) stabilizer, shown in Fig. 1. This cross section is identical to that of the conductor proposed for a larger SMES coil [l]. The total conductor length in the POPE test coil, including the leads, is 11 meters. A schematic layout of the test coil is shown in Fig. 2 In its original configuration, the conductor for the POPE test coil did not have any strand joints. The stabilizer contained one joint, approximately in the middle of its length. This joint was made by flash butt welding of the aluminum prior to inserting the strands into the groove during the initial construction of the test coil in 1989, and has operated well ever since.A full size SMES will contain many stabilizer and strand joints. These joints will be made at the construction site as the coil is being wound, and are thus called "field joints." The proposed field joint consists of a flash butt welded joint in the aluminum stabilizer, and cold upset welds in each of the eight superconducting strands. For each weld the upset material is trimmed away, so that the cross section of the conductor is maintained through the joint area. In general, joints would not be noticeable, except under close visual inspection. Since the conductor is immersed in a helium bath, there are no cryostat or conduit joints that must coincide with the conductor joint.A failure in the positive lead of the POPE test coil occurred in August 1993. The failure occurred due to current being applied during a RR test at 15 K for an excessive period of time. The aluminum conductor and superconducting strands melted in a section of the positive lead at the location shown in Fig. 2. This failure required a rapid fix in order to finish the POPE testing on schedule and presented the opportunity of testing a repair similar to the proposed field joint in a large SMES.The POPE test coil is repaired in one month, allowing completion of the test program on schedule. Despite tight schedule and significant technical constraints caused by the nature of the in-situ repair, a satisfactory joint is produced. In this report, we describe the fabrication and performance of this joint. Through this effort, we...
