Magnetically accelerated, ultrahigh velocity flyer plates for shock wave experiments

Abstract

The intense magnetic field produced by the 20 MA Z accelerator is used as an impulsive pressure source to accelerate metal flyer plates to high velocity for the purpose of performing plate impact, shock wave experiments. This capability has been significantly enhanced by the recently developed pulse shaping capability of Z, which enables tailoring the rise time to peak current for a specific material and drive pressure to avoid shock formation within the flyer plate during acceleration. Consequently, full advantage can be taken of the available current to achieve the maximum possible magnetic drive pressure. In this way, peak magnetic drive pressures up to 490 GPa have been produced, which shocklessly accelerated 850μm aluminum (6061-T6) flyer plates to peak velocities of 34km∕s. We discuss magnetohydrodynamic (MHD) simulations that are used to optimize the magnetic pressure for a given flyer load and to determine the shape of the current rise time that precludes shock formation within the flyer during acceleration to peak velocity. In addition, we present results pertaining to plate impact, shock wave experiments in which the aluminum flyer plates were magnetically accelerated across a vacuum gap and impacted z-cut, α-quartz targets. Accurate measurements of resulting quartz shock velocities are presented and analyzed through high-fidelity MHD simulations enhanced using optimization techniques. Results show that a fraction of the flyer remains at solid density at impact, that the fraction of material at solid density decreases with increasing magnetic pressure, and that the observed abrupt decrease in the quartz shock velocity is well correlated with the melt transition in the aluminum flyer.

Penetration of Rod Projectiles in Semi-Infinite Targets: A Validation Test for Eulerian X-FEM in Alegra

“…work by Lemke et al (2005) [14] for magnetically accelerated flyer plates; and Doney et al (2010) [7] for exploding wires, among others.…”

Analysis of cylindrical ramp compression experiment with radiography based surface fitting method

“…The beryllium liner is directly driven with a current pulse shape with a time rate of change in the drive pressure that avoids shock formation in the liner [4] and allows for the inner surface to be quasi-isentropically compressed since the magnetic diffusion wave is ahead of the thermal conduction wave. The design of the drive pressure made use of the LANL SESAME Be2020 equation of state.…”

“…Since only two radiograph frames are available per experiment, two experiments were performed with radiographs acquired at machine times 3.027 μs, 3.035 μs, 3.046 μs and 3.050 μs. The load current of the two experiments was repeated to within two percent as determined by VISAR unfold [4] and the radiograph timings between experiments has an uncertainty of order 300 ps.…”

“…The ability to achieve megabar drive pressures from a magnetic field, along with the capability to control the shape of the current drive over many hundreds of nanoseconds, has proved valuable for both shock [4] and ramp compression [5] experiments in the high energy density regime. The bulk of these magnetically-driven dynamic materials experiments are performed in divergent geometries [6] for which P ∝ I 2 L −2 0 where P is the drive pressure, I is the drive current, and L 0 is a constant scale factor dependent upon the initial geometry of the system.…”

Magnetohydrodynamics of Metallic Foil Electrical Explosion and Magnetically Driven Quasi-Isentropic Compression

“…As J.R. Asay said, it will be a new experimental technique widely used in shock dynamics, astrophysics, high energy density physics, material science and so on. The process of magnetically driven quasi-isentropic compression is typical magnetodynamics [14] , which refers to dynamic compression, magnetic field diffusion, heat conduction and so on. As described above, the electrical explosion of metallic foil and magnetically driven quasiisentropic compression is typically magnetohydrodynamic problem.…”