Helical plasma striations in liners in the presence of an external axial magnetic field

Abstract

Awe et al. found on the 20 MA Z machine [Acta Phys. Pol. A 115, 956 (2009)] that applying an externally generated axial magnetic field to an imploding liner leads to a helical pattern in the liner when viewed with soft x-ray radiography ([Phys. Rev. Lett. 111, 235005 (2013)] and [Phys. Plasmas 21, 056303 (2014)]). Here, we show that this phenomenon is also observed in extreme ultraviolet self-emission images of 10 mm long cylindrical metal liners having varying diameters and varying wall thicknesses on a 1 MA, 100–200 ns pulsed power generator. The magnetic field in these experiments is created using either twisted return current wires positioned close to the liner, generating a time-varying Bz, or a Helmholtz coil, generating a steady-state Bz.

Pulsed-power-driven cylindrical aluminium liner implosions with a high aspect ratio at an 8 MA facility

“…Striation features were clearly observed and developed in those experiments. Similar striations were observed on the 1 MA COBRA with a gated extreme ultraviolet (XUV) imaging diagnostic [21]. Quantitatively, the striation features are quasi-periodic structures with characteristic axial wavelengths of ∼ 1.67 mm at −59.8 ns and ∼ 2.24 mm at −45.8 ns, obtained by averaging over all the distances between the centers of all adjacent bumps.…”

Self-generated plasma rotation in a Z-pinch implosion with preembedded axial magnetic field

“…Z-pinch implosions with preembedded axial magnetic fields (B z0 ) have been intensively studied during the last decade [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] due to their importance both for inertial confinement fusion [1,2,8,9] and for the study of fundamental plasma physics [18,19]. A primary difference from standard Z-pinches (without B z0 ) is that during the implosion not only the plasma is compressed, but also the axial magnetic field, leading to a profound effect on the implosion dynamics.…”

Controlling Rayleigh-Taylor Instabilities in Magnetically Driven Solid Metal Shells by Means of a Dynamic Screw Pinch

“…Furthermore, no enhancement of x-ray/neutron production was observed in these systems. For each of these experiments, significant magnetic field penetration into the target is possible (and often measured [12,57]), invalidating a simple ideal MHD picture and suggesting that magnetic shear may play a role, but this remains an open question. In stark contrast, thick metal liners are much more amenable to an ideal MHD treatment like V&S, and the dominant physics influencing the MRTI-including the dynamic-polarization stabilization exhibited by the SLDSP-is less ambiguous.…”

“…Dynamic B z generation in thin foil [12], gas puff [55,56], and wire array [57] experiments demonstrated qualitative impacts on stability. However, detailed analyses of these experiments are lacking, and our understanding of MRTI in these complex systems is either cursory [58,59] or nonexistent.…”

“…Reducing MRTI growth could enable the use of thinner (and possibly higher-density) liners, increasing achievable peak shell velocities, stagnation pressures, and/or fuel confinement times. Extensive experimental and computational work has examined the formation [9][10][11][12] and evolution [5,[13][14][15][16][17][18] of MRTI in metal liners. Several authors also examine RTI in cylindrical shells analytically [8,[19][20][21][22][23][24].…”