62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020;
Remote; Time Zone: Central Standard Time, USA
Session PI01: Invited: HED Fundamental Plasma Physics
2:00 PM–5:00 PM,
Wednesday, November 11, 2020
Chair: Cameron Geddes, LBNL
Abstract: PI01.00001 : Liner Implosion Experiments Driven by a Dynamic Screw Pinch
2:00 PM–2:30 PM
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Abstract
Author:
Paul Campbell
(Univ of Michigan - Ann Arbor)
Magnetically driven implosions are susceptible to magnetohydrodynamic
instabilities, including the magneto-Rayleigh-Taylor instability (MRTI). The
use of a dynamic screw pinch (DSP) has been proposed [1], to control the
MRTI growth in sold-metal liner implosions. In a DSP configuration a helical
return-current structure surrounds the liner, resulting in a helical
magnetic field that drives the implosion. Using the 1-MA, 100--200-ns COBRA
pulsed-power driver at Cornell, we present experimental tests of three DSP
cases (with peak axial magnetic fields of 2 T, 14 T, and 20 T) as well as a
standard z-pinch (SZP) case [2]. The liners had an initial radius of 3.2 mm
and were made from 650-nm-thick aluminum foil. Micro B-dot probes measured
the axial magnetic fields produced by the return current structures. A probe
placed inside the liner measured the axial field injected into the liner's
interior prior to the implosion and the degree of flux compression during
the implosion. Load current measurements made in COBRA's power feed suggest
that the amount of low-density plasma flowing in the power feed after peak
current is reduced in the DSP cases. Imaging revealed that helical MRTI
modes developed in the DSP cases while azimuthally correlated MRTI modes
developed in the SZP case and that the MRTI amplitudes for the 14-T and 20-T
DSP cases were smaller than in the SZP case. Specifically, when the liner
had imploded to half of its initial radius, the MRTI amplitudes for the SZP
case and for the 14-T and 20-T DSP cases were, respectively, 1.1\textpm 0.3
mm, 0.7\textpm 0.2 mm, and 0.3\textpm 0.1 mm. Relative to the SZP, the
stabilization obtained using the DSP agrees reasonably well with theoretical
estimates.
This work was conducted in collaboration with T. M. Jones, J. M. Woolstrum,
N. M. Jordan, and R. D. McBride (U. Michigan), P. F. Schmit (Sandia), and J.
B. Greenly, W. M. Potter, E. S. Lavine, B. R. Kusse, D. A. Hammer (Cornell).
This work was supported by NSF Grant PHY-1705418 of the NSF-DOE Partnership
in Basic Plasma Science and Engineering. COBRA support was provided by the
NNSA SSAP under DOE Cooperative Agreement DE-NA0003764.
[1] P. F. Schmit \textit{et al.}, Phys. Rev. Lett. \textbf{117}, 205001 (2016).
[2] P. C. Campbell \textit{et al.}, ``Stabilization of Liner Implosions via a Dynamic Screw
Pinch'', accepted in Phys. Rev. Lett. (2020).