Quantitative Measurements of Ablation in Wire Array Z-Pinches

Abstract

Summary form given only. We report on detailed density measurements of the ablating plasma in wire array z-pinch experiments. Previously such measurements have been restricted to relatively early times in an experiment, where laser probing could penetrate the ablated plasma without being refracted by steep gradients. Here we show measurements made by 2 new diagnostics that compliment the earlier laser based data. In one system XUV point projection backlighting is used to probe both the ablated plasma streams and the precursor plasma column formed on the axis of the array by collision of the streams. Radiation for the back lighter is produced by a 5.1 laser pulse focused to a Cu target within a few cm of the array. Recording is via a large format MCP camera. In the second system, the KeV radiation from an X-pinch is projected along the axis of an array. Using this probing direction the relatively long lengths of plasma provide significant absorption of the probing radiation even at the multi KeV energies produced by the X-pinch, allowing good estimates of the plasma density. Results of experiments utilizing the diagnostics are compared to the rocket ablation model and 2 and 3-D MHD simulations. Attempts are now being made to improve both the XUV and hard X-ray systems by using spherical multilayer mirrors (for XUV) and spherical crystals (for X-pinch) to project parallel beams of monochromatic radiation through the array. This will allow absolute density measurements of the ablated plasma.