Solid liner implosions on Z for producing multi-megabar, shockless compressions

Abstract

Current pulse shaping techniques, originally developed for planar dynamic material experiments on the Z-machine [M. K. Matzen et al., Phys. Plasmas 12, 055503 (2005)], are adapted to the design of controlled cylindrical liner implosions. By driving these targets with a current pulse shape that prevents shock formation inside the liner, shock heating is avoided along with the corresponding decrease in electrical conductivity ahead of the magnetic diffusion wave penetrating the liner. This results in an imploding liner with a significant amount of its mass in the solid phase and at multi-megabar pressures. Pressures in the solid region of a shaped pulse driven beryllium liner fielded on the Z-machine are inferred to 5.5 Mbar, while simulations suggest implosion velocities greater than 50kms-1. These solid liner experiments are diagnosed with multi-frame monochromatic x-ray backlighting which is used to infer the material density and pressure. This work has led to a new platform on the Z-machine that can be used to perform off-Hugoniot measurements at higher pressures than are accessible through magnetically driven planar geometries.

Stability of fusion target concepts on Z.

“…The short pulse mode current used in 2104 drives a shock into the liner, which is evident as a step in velocity at time 3.06e-6 s. In contrast, there is no evidence of shock up in the 2207 liner velocity; the load current for 2207 is designed to accelerate the Be liner shocklessly [10], which was evidently successful. Filled contours of simulated liner density are plotted in Figure 16 for both shots, at times when the liner inner surfaces are at approximately the same position.…”

“…This pressure is several times what could be achieved in the standard planar geometry [8]. Significantly more detail on this work can be found in these publications [8,9,10]. This LDRD project contributed to the development of the targets, radiography diagnostics, and hardware platform used in these experiments, however, most of the work specific to these experiments was funded by the Dynamic Materials Program at Sandia.…”

“…Thus, the main thrust of this LDRD proposal was to study the key physics issue of liner stability. These experiments were extremely successful and resulted in several high-profile publications [6,7,8,9,10,11,12]. The results of these studies are summarized in Section 2.…”

“…The liner shocks up during acceleration in 2104; it is shocklessly accelerated in 2207 [10]. Solid liners composed of Be, density ρ=1.85 g/cc, coaxial with a 1.3 cm radius anode return current can, also composed of Be, were used in both shots.…”

“…The experiments used radiography images of the liner implosions to infer the radial density profile at several times during the implosion. A detailed, self-consistent method was developed for using the radiography data to infer the pressure and density in the material [9,10], and peak pressures up to 5.5 Mbar were inferred from the data. This pressure is several times what could be achieved in the standard planar geometry [8].…”