Nonaxisymmetric behavior of the central solenoid spiral cut pancakes for the Burning Plasma Experiment

The central solenoid for the Burning Plasma Experiment (BPX) is made up of spiral cut pancakes which are water-jet cut from plate. Two of these pancakes are joined at the ID, one plate having been turned over. Double-pancake modules are then stacked and jointed at the outside to form the full solenoid. Routing the inner turn around the inner joint to continue as the second turn introduces a region where structural and current behavior deviates from axisymmetry. The effect on peak stress is shown to be significantly less than previously reported. Cyclic symmetry model boundary conditions, avoidance of inner turn separation, and consistent geometries for field and structural calculations are key elements in revealing the minimal effect of the transition region. Based on optimum local joint characteristics, a 3% increase in hoop stress is recommended for the BPX central solenoid to address transition region effects