Ablation dynamics and stagnation physics of copper wire array Z-pinch implosions at 20 MA

K-shell x-rays have been studied with various materials at the 20-MA (pre-refurbished) Z accelerator. This paper presents results obtained for the ablation dynamics and stagnation physics of single and nested copper Z-pinches with varying initial load diameters. Monochromatic imaging and shadowgraphy provide detailed information regarding the ablation of the wires and the initial implosion, including instability growth. Time-resolved pinhole images near stagnation illustrate a cold blanket (≪ 1 keV, several mm diameter)/hot core (≫ 1 keV, ∼ 1mm diameter) structure and are used to provide estimates of the late time implosion velocity. Plasma parameters extracted from modeling of time-integrated K-shell spectra, as well as L-shell spectra, also suggest that temperature gradients are present in the plasma. Measurements of the Cu K-shell yield are also presented, although it generally appears that bright spots dominate the K-shell radiation pulse for single arrays. The experimental results will be compared with multi-dimensional Gorgon calculations, as well as a K-shell scaling theory.