Insights and applications of two-dimensional simulations to Z-pinch experiments

Abstract

A two-dimensional (2D) Eulerian radiation-magnetohydrodynamic code has been used to successfully simulate hollow metallic z-pinch experiments fielded on several facilities with a wide variety of drive conditions, time scales, and loads. The 2D simulations of these experiments reproduce important quantities of interest including the radiation pulse energy, power, and pulse width. This match is obtained through the use of an initial condition: the amplitude of a random density perturbation imposed on the initial plasma shell. The perturbations seed the development of magnetically driven Rayleigh–Taylor instabilities which greatly affect the dynamics of the implosion and the resulting production of radiation. Analysis of such simulations allows insights into the physical processes by which these calculations reproduce the experimental results. As examples, the insights gained from the simulations of Sandia “Z” accelerator [R. B. Spielman et al., Phys. Plasmas 5, 2105 (1998)] experiments have allowed for the investigation of possible physical processes which produce high powers in “nested array” implosions and high temperatures within “dynamic hohlraum” loads. Building on these insights, the 2D code has been used in designing new experiments to optimize the desired physical conditions and in interpreting the experimental results obtained. These examples and others will be discussed as well as examples of simulation results where improvement is needed and what steps are being taken to make that improvement.

Dynamics of a Z-pinch x-ray source for heating inertial-confinement-fusion relevant hohlraums to 120–160 eV

“…5), and is referred to as the time of stagnation in the following figures. In this baseline E-RMHC model, the random density perturbation used to seed the RT instability in the outer shell has been chosen so that the off-axis radiated power pulse matches those measured in experiments for a pinch without an axial target [34]. Using this~rturbation (random fluctuations in density varying +670 seeded into each O.lmm x O.lmm zone), the shape of the calculated off-axis power is bracketed by that measured (Fig.…”

“…Simulations of the imploding wire arrays using the Scnnmer circuit code [49,50] and a baseline 2D E-RMHC model [34] are illustrated in Fig When two shells collide, momentum is conserved and the mass of the inner shell is accrued to the outer one, which continues to accelerate inward to the next collision (resulting in a discontinuity in velocity and kinetic energy at the time of the collision Fig. 4C]).…”

“…The slope of the wire-array glide plane, betwtxm the inner array and the targe~is set to 3 degrees (Fig. lD) to prevent premature sliding of tungsten plasma across the REH, which would block the radiation generated in the target from reaching the hohlraum [34]. To minimize the efftxt of variations in the magnetic pressure acting on the imploding array, the current-return surrounding the load is solid except for a 3-mm diameter hole, which permits the radiation external to the target to be monitored.…”

“…These target high energy-density simulations [32][33][34] provide insight into the underlying dynamics. The simulations; take into account the development of the magnetically-driven RT (Rayleigh-Taylor) instability in the r-z @ane of the imploding tungsten load, x-ray generation as the tungsten plasma strikes the target, and radiation transport to the hohlraum.…”

Hot Dense Capsule-Implosion Cores Produced byZ-Pinch Dynamic Hohlraum Radiation

“…The fill was 2.8 atm CD 4 + 0.085 atm Ar. CD 4 was chosen to avoid the difficulty of retaining D 2 inside large-diameter thin-CH-wall capsules.…”