Demonstrated transparent mode in nested wire arrays used for dynamic hohlraum Z pinches

The mass of the outer and inner wire array used to drive the baseline dynamic hohlraum (DH) with pedestal target [Sanford et al. , Phys. Plasmas 13, 012701 (2006)] is reversed in order to determine if the nested wire array is operating in a hydrodynamic, or transparent-like mode [J. Davis et al. , Appl. Phys. Lett. 70, 170 (1997)], when the outer array arrives at the radius of the inner array. In contrast to the baseline, mass reversal allows the modes to be distinguished by the difference in the timing of characteristic features of the x-ray radiation pulses in the two modes. For the reversed-mass DH, all parameters such as wire number, array radii, and target remained the same, except the diameters of the individual wires were adjusted to reverse the array masses. Measurements show unambiguously that the reversed-mass DH operates in a transparent-like mode, the outer array passing through the inner array with limited collisional interaction. Numerical simulations in the r - θ plane suggest that the underlying physics of the outer array collision with the inner between the two DHs (baseline and reversed-mass), remains similar, implying that the baseline also operates with transparency. Inflection in the rate of change of the current is measured 4 – 7 ns after the radiation signal and is associated with the outer-inner array interaction, indicating that the rear portion of the resulting plasma shell of the outer array carries the current prior to the collision. Numerical simulations together with analytic theory describe probable dynamics of the current switching from the outer to inner array.