Effect of Current Rise-time on the Formation of Precursor Structures and Mass Ablation Rate in Cylindrical Wire Array Z-Pinches

We present the first study to directly compare the mass ablation rates of cylindrical wire arrays as a function of the current rise-rate. Formation of the precursor column is investigated on both the MAPGIE (1 MA, 250ns) and COBRA (1 MA, 100ns) generators, and results are used to infer the change in the mass ablation rate induced by the rise-rate of the drive current. Laser shadowography, gated XUV imaging and x-ray diodes are used to compare the dynamical behavior both generators, and x-pinch radiography and XUV spectroscopy and provide density evolution and temperature measurements respectively. Results are compared to predictions from an analytical scaling model based on a fixed ablation rate, and the close correlation achieved suggests that the effective ablation velocity is not a strong function of the current rise rate.