Power enhancement from nested titanium wire arrays with foam targets on the Z accelerator

Summary form only given, as follows. In the years since the 20 MA Z accelerator has come online, many experiments have been performed to study the radiation emitted from wire array Z-pinches. Several K-shell sources have been studied in recent years at Z, including aluminum, titanium, stainless steel, nickel, and copper. Observations from these experiments show that low wire number (interwire gaps >0.7 mm) nested arrays produce higher powers with narrower pulsewidths and faster risetimes than single wire arrays. They also produce smaller diameter pinches with improved axial uniformity, and higher plasma temperatures and densities. Theory suggests that this improvement could result from the mitigation of the Rayleigh-Taylor instability, and reduced asymmetry development due to current switch between arrays. Spectral analyses indicate that the radiation output in the K-shell is limited due to low densities and low mass fractions, however. To investigate one method for increasing the density on-axis, low Z foam targets have been used at the center of nested wire arrays. The foams could lead to additional improvements in the stagnation and implosion stability. TPX foams with densities of 10 - 30 mg/cm/sup 3/ and diameters of 2.0-2.8 mm were mounted at the center of 50 mm diameter nested nickel-clad titanium wire arrays. This nested wire array configuration has been fielded numerous times with no target and therefore provides excellent comparative data. The presence of the foam target resulted in an enhancement of the total radiated power from 120 TW (no foam) to 160 TW (30 mg/cm/sup 3/). The Kshell power increased from 8 TW to 11 TW. These improvements likely result from decreases in pulsewidth that were observed; the K-shell FWHM decreased from 7ns (no foam) to 4 ns (30 mg/cm). The risetimes were relatively constant. In general, the pulsewidth decreased, and the power increased, with increased foam density. The radiated yields remained similar to the loads with no foam, however. In this paper, the results of the foam target experiments will be presented and compared to nested and single aff ay experiments without targets.