Technique for fabrication of ultrathin foils in cylindrical geometry for liner-plasma implosion experiments with sub-megaampere currents

Abstract

In this work, we describe a technique for fabricating ultrathin foils in cylindrical geometry for liner-plasma implosion experiments using sub-MA currents. Liners are formed by wrapping a 400 nm, rectangular strip of aluminum foil around a dumbbell-shaped support structure with a non-conducting center rod, so that the liner dimensions are 1 cm in height, 6.55 mm in diameter, and 400 nm in thickness. The liner-plasmas are imploded by discharging ∼600 kA with ∼200 ns rise time using a 1 MA linear transformer driver, and the resulting implosions are imaged four times per shot using laser-shadowgraphy at 532 nm. This technique enables the study of plasma implosion physics, including the magneto Rayleigh-Taylor, sausage, and kink instabilities on initially solid, imploding metallic liners with university-scale pulsed power machines.

A Primer on Pulsed Power and Linear Transformer Drivers for High Energy Density Physics Applications

“…III, we find Z 0 = L/C ≈ 0.16 Ω, I peak = V 0 /Z 0 ≈ 900 kA, and τ peak = (π/2) √ LC ≈ 200 ns. These results agree reasonably well with experiments conducted on MAIZE [29], [108]- [112], especially given the simplicity of the LC model. Note that with V c = ±70 kV (|V 0 | = 2|V c | = 140 kV), the initial energy stored in the MAIZE capacitors is…”

Seeded and unseeded helical modes in magnetized, non-imploding cylindrical liner-plasmas

“…15 The two types of non-imploding targets used were unseeded and kink-seeded ultrathin liners, fabricated using a technique similar to Ref. 16. For this experiment, the targets were fabricated by directly wrapping the foil around an unmodified straight-cylindrical or threadedcylindrical (1/4 00 -20 imperial) plastic rod.…”

Evolution of sausage and helical modes in magnetized thin-foil cylindrical liners driven by a Z-pinch

“…The liner loads were fabricated using a rectangular (2.2 cm  1.2 cm) aluminum foil (400-nm thick) wrapped around a cylindrical support structure, where the support structure consisted of two conducting ends (outer diameter, OD ¼ 6.55 mm) and a dielectric center, which was either solid-cylindrical (OD ¼ 6.35 mm) or dumbbell-shaped (OD ¼ 1-2 mm) 16 [see Fig. 1(c)].…”

“…When kA is small, the instability growth may be modeled by linear perturbation theory (recall that the product kA can be used as the dimensionless expansion parameter in a nonlinear theory). The linear theory, which yields simple exponential growth, fails 23 if kA > 1, i.e., if A=k > 0: 16. The values of instability wavelength are plotted as a function of time for shot 1189 (B z ¼ 0 T) in Fig.…”

“…Thus, a new platform was developed at the University of Michigan to experimentally investigate cylindrical MHD and MRT instabilities on MAIZE using aluminum liners with a wall thickness of 400 nm. 16 This platform accommodates three experimental configurations, which were designed to investigate: (1) MHD instabilities in a non-imploding geometry, where the plasma acceleration, and thus the coupling to the MRT instability, is minimized; (2) MHD-MRT coupled instabilities in an imploding geometry; and (3) the effects of the magnitude and direction of an applied axial magnetic field on a seeded m ¼ 1 kink instability.…”