Magnetic liner implosion simulations for the ALT-3 experiment

We discuss two-dimensional magnetohydrodynamic simulations of the liner implosion, which model the development of Rayleigh-Taylor-like instability and interaction between the liner and PU glide planes. The simulations were conducted with variations in methodological parameters (random initial perturbations etc.) and in the glide plane shape. We found a glide plane shape that provides reliable electric contact with the liner during implosion and acceptable shape of the liner's front surface before the impact without jets that are dangerous for diagnostics of the liner as an impactor.

I. Introduction

Magnetic implosion of cylindrical liners can be of interest for shock experiments to measure Hugoniots in test materials at terapascal-range pressures [1]–[10]. In the envisaged LANL/VNIIEF joint explosive magnetic experiment ALT – 3, similar to ALT-1, 2 [2]–[3], we are planning to use an aluminum liner having a radius of 40 mm, height of ~ 40 mm and thickness of 3 mm [4]. 1D MHD simulations predict that with an expected drive current of 60–70 MA (azimuthal magnetic fields of 4–5 MGs) temperatures near the liner's back surface at the end of implosion can be as high as ~ 15 e V, but up to ~50% of liner mass adjacent to the front surface can remain solid and have a velocity of ~20 km/s at an impact radius of ~ l cm. The system chosen for the ALT-3 experiment [4] provides currents in the liner ponderomotive unit (PU) without precursor (Figs. 1a-b; current waveform I₄). With such a current waveform, major 2D effects of magnetically-driven liner implosion, such as the development of Rayleigh-Taylor-like instability and interaction with copper electrodes (glide planes), in 2D MHD simulations are weaker than with current waveforms having a precursor (Fig. 1a; current waveform I₅). As evidenced by simulations, liner/glide plane interaction effects can mostly involve the liner regions at the liner/glide plane interface. The central problem in liner implosion is the development of liner instability. Figure 1:

The ALT-3 experiment: possible current waveforms (a) and initial PU shape (b).