Double planar wire arrays at enhanced current on Zebra

Double Planar Wire Arrays (DPWA), which consist of two parallel rows of wires, have demonstrated high radiation efficiency (up to 30 kJ), compact size (1.5-3 mm), and pulse shaping capabilities in experiments at 1 MA Zebra. DPWAs are also very suitable for the new compact multi-source hohlraum concept. It was shown that their implosion dynamics strongly depends on the critical load parameter, the aspect ratio (width to inter-planar gap Δ). Recently, we studied larger sized DPWAs at the increased current of 1.5-1.7 MA that provided enhanced energy coupling in plasma and better diagnostic access to observable plasma regions. The new regimes of implosions with asymmetric jets, no precursor formation and very early radiation for larger sized DPWAs (Δ=9 mm) with low aspect ratio of 0.54 were demonstrated. As a development of this work, new experiments at the enhanced current with the DPWAs from Alumel (mostly Ni) with Δ=6 mm and higher aspect ratio were performed. The different implosion and radiative signatures were observed that are presented and analyzed such as formation of the precursor in the middle of the array, no “foot” pulse emission but a very broad XRD signal, and L-shell radiation before the XRD peak but not so early as for larger PWAs. Also, simultaneously with soft x-ray L-shell Ni radiation, hard x-ray K-shell Ni radiation was recorded in a broad range from 13 ns before up to 18 ns after the XRD peak showing the temporal evolution of characteristic “cold” Ni Kα emission as well as some adjacent spectral features from hotter plasmas. Non-LTE modeling of such K-shell features provided time history of ionization balance of Ni ions and is compared with results of L-shell modeling.