Observation of >400-eV Precursor Plasmas from Low-Wire-Number Copper Arrays at the 1-MA Zebra Facility

Experiments with cylindrical copper wire arrays at the 1-MA Zebra facility show that high temperatures exist in the precursor plasmas formed when ablated wire array material accretes on the axis prior to the stagnation of a z pinch. In these experiments, the precursor radiated approximately 20% of the >1000 eV x-ray output, and time-resolved spectra show substantial emission from Cu L-shell lines. Modeling of the spectra shows an increase in temperature as the precursor forms, up to ∼450 eV, after which the temperature decreases to ∼220-320 eV until the main implosion