Enhanced stability of imploding liners caused by material strength

Implosion stability is a key issue for magnetically driven liners, with the magneto-Rayleigh-Taylor (MRT) instability providing one of the main challenges for magneto-inertial fusion schemes such as MagLIF [1]. Late-time growth of the MRT instability is strongly influenced by early time behaviour, which is determined not only by the liner material and surface finish, but also the shape of the current drive, and especially how it influences melting and vapourisation of the liner outer edge.

A known stabilisation mechanism for the MRT instability is material strength, however this is usually insignificant for fast liner implosions. Liner implosion experiments carried out in 2002 on a 6 MA, 7 μs rise-time machine by Reinovsky et al [2] demonstrated stable implosion of very high aspect ratio (AR~60) liners. Using our 3D MHD code B2, we present simulations of these experiments with and without material strength, demonstrating how it can significantly enhance implosion stability.

Furthermore, we present work on the design and implosion of high aspect ratio liners on our 8 MA, 1.5 μs pulsed power machine M3, where implosion parameters have been optimised to maximise the time that material strength is important and hence to minimise MRT instability growth.

[1] Slutz et al, Physics of Plasmas 17, 056303 (2010)

[2] Reinovsky et al, IEEE Transactions on Plasma Science 30, 5 (2002)