The Calculated and Measured Resistance for Splices between Conductors in a MICE Superconducting Coil

Abstract

The resistance of superconducting joints within MICE coils is an important issue particularly for the coupling coils. The MICE tracker solenoids have only two superconducting joints in the three spectrometer set (end coil 1, the center coil and end coil 2). The AFC magnets may have only a single joint within the coil. The coupling coils may have as many as fifteen joints within the coil, due to relatively short piece lengths of the superconductor. LBNL and ICST looked at three types of coil joints. They are; 1) cold fusion butt joints, 2) side-by-side lap joints, and 3) up-down lap joints. A theoretical calculation of the joint resistance was done at LBNL and checked by ICST. After looking at the theoretical resistance of the three types of joints, it was decided that the cold welded butt joint was not an attractive alternative for joints within a MICE superconducting magnet coil. Side-by-side and up-down lap joints were fabricated at ICST using two types of soft solder between the conductors. These conductor joints were tested at LBNL at liquid helium temperatures over a range of magnetic fields. The joint resistance was compared with the theoretical calculations. Measurements of splice strength were also made at 300 K and 77 K.

Results from the Cooler and Lead Tests

“…These errors in the measurement voltage could be due to noise in the system. In any event, the resistance data for the splices suggests splice resistances in the tens of n-ohm range [28], [29], which very difficult to measure. The volt meters used for the splice resistance tests at Berkeley are much better than the volt meter used in the vendors shop.…”

“…In general, the splices used in the cooler-lead experiment were half the length of the same splices in the spectrometer magnet. In general, the I 2 R heating of the splices should be inversely proportional to their length [28], [29]. Figure 4 shows an electrical schematic of the cooler-lead experiment.…”

The Resistance and Strength of Soft Solder Splices Between Conductors in MICE Coils

“…This technique allows one to separate the signal voltage from the noise, so that one can determine the IR voltage across the splice. This technique yields more accurate measurements than the technique used for measuring splice resistance in 2008 [3].…”

“…The resistance of several 1000 mm long side-by-side and up-down hand made splices was measured in 2008 [3], [4]. These splices were made using Sn96-Ag.3.5-Cu0.5 solder (a lead free tin-silver soft solder commonly used for electronics) and Sn63-Pb37 solder (tin-lead eutectic solder).…”

“…Fig. 1 shows the three types of normal splices were studied; cold welded butt splices, soldered up-down lap splices, and soldered side-by-side lap splices [3], [4]. The fabricators for the coupling magnet [5] and the AFC magnet [6] have chosen to make their splices at the ends of a layer, so that the splice is a transition from one layer to the next.…”