Tungsten wire-array dynamics and power variations from 20 mm arrays on the Sandia Z facility

Summary form only given. The radiation source for Z-pinch-driven hohlraum, inertial confinement fusion (ICF) tests on the 20 MA Z facility is a single (or nested) 20 mm diameter tungsten wire array. Full-scale ICF designs call for these arrays to be driven by currents of about 60 MA. To ensure that the scaling requirements of these loads are well understood, we conducted an extensive set of experiments to characterize the performance of these arrays. These tests used a comprehensive set of diagnostics developed for this purpose, including monochromatic 1865 eV and 6151 eV crystal backlighters, 527 nm optical shadowgraphy diagnostics, and various X-ray self-emission diagnostics. During these experiments, the wire array diameter (20 mm), height (10 mm), and wire number (300) were kept constant, but the mass of the array was varied (by altering the initial wire diameters) to obtain substantially different implosion times. Statistics were obtained at total masses of 1.14 mg, 2.5 mg, and 6.0 mg (65 ns, 81 ns, and 100 ns implosion times, respectively), resulting in average peak powers of about 100 TW, 120 TW, and 95 TW, respectively. The higher powers obtained using lower masses are notable because the peak currents achieved were lower due to the shorter implosion times (12.7 MA, 16.3 MA, and 17.3 MA, respectively.) Radiography and shadowgraphy measurements of these arrays show that they retain core/corona structure until 55-60% of the total implosion time. Once the core/corona structure disappears, the arrays appear nominally shell-like and the bulk of the mass starts to move radially inward. Radiography measurements at the same absolute time during the implosion suggest that the ablation dynamics of each array are identical up until the start of the array motion. We present the experimental results and hypotheses for these trends.