An investigation into the effects of high cycle fatigue on REBCO coils along their axis of rotation was performed to establish design limits. Three coils were tested in liquid nitrogen via a hydraulic materials testing machine. The coils were fabricated with the same type of REBCO tape but had different co-wind materials and dimensions. The results showed that for a coil with REBCO tape wider than its co-wind, where the loads bear directly on the conductor, had 5% permanent critical current degradation at pressures near 100 MPa. A significant improvement was observed in a wax impregnated coil, which aided to distribute loads, with a 1.2% permanent critical current reduction after 50,000 load cycles to 125 MPa. Additionally, a coil with co-wind wider than its REBCO tape was also improved and reached 5% reduction after 50,000 cycles at pressures up to 100 MPa and continued loading to 151 MPa.

During the NHMFL 32 T magnet project, a program to develop a reliable method for making soldered lap joints between REBCO tape conductors was initiated. A standard process was adopted during the program, and then applied during coil fabrication and for quality control (QC) of incoming conductor. For each unique REBCO conductor piece procured for the 32 T project, a lap solder joint was made using the standard process and tested for resistance in liquid nitrogen. A total of 211 lap joints were made and tested. For the NHMFL 40 T magnet project, a similar study was performed using the same standard process on conductors procured for test coils. A total of 38 lap joints were made and tested. Results from both data sets are reported, and compared with findings from the initial study and published findings by others. In the stacked double-pancake construction adopted by the NHMFL for REBCO coils, each double-pancake is connected in series to adjacent modules with a crossover connection, made from an assembly of several REBCO tapes placed in parallel and soldered across the terminal ends of each adjacent module. Resistances of the crossovers in a 32 T test coil and from test articles and test coils made during the 40 T project, are reported here. The resistivity of the crossovers is estimated and compared with the findings from the lap joint measurements.

Zylon fibers, which are made of high-strength polymer, are used at the National High Magnetic Field Laboratory for structural reinforcement of high field pulsed magnet coils. Most polymers are subject to chain scission, which is the result of aging degradation of the fibers in the absence of chemical agent. We studied chain scission of Zylon fibers stored with and without visible light. No mechanical strength degradation was found in Zylon stored without exposure to visible light for 8 years. Prolonged exposure to lab-lighting rendered formation of surface defects, resulting in reduction in mechanical strength.