Modified helix-like instability structure on imploding z-pinch liners that are pre-imposed with a uniform axial magnetic field

Abstract

Recent experiments at the Sandia National Laboratories Z Facility have, for the first time, studied the implosion dynamics of magnetized liner inertial fusion (MagLIF) style liners that were pre-imposed with a uniform axial magnetic field. As reported [T. J. Awe et al., Phys. Rev. Lett. 111, 235005 (2013)] when premagnetized with a 7 or 10 T axial field, these liners developed 3D-helix-like hydrodynamic instabilities; such instabilities starkly contrast with the azimuthally correlated magneto-Rayleigh-Taylor (MRT) instabilities that have been consistently observed in many earlier non-premagnetized experiments. The helical structure persisted throughout the implosion, even though the azimuthal drive field greatly exceeded the expected axial field at the liner's outer wall for all but the earliest stages of the experiment. Whether this modified instability structure has practical importance for magneto-inertial fusion concepts depends primarily on whether the modified instability structure is more stable than standard azimuthally correlated MRT instabilities. In this manuscript, we discuss the evolution of the helix-like instability observed on premagnetized liners. While a first principles explanation of this observation remains elusive, recent 3D simulations suggest that if a small amplitude helical perturbation can be seeded on the liner's outer surface, no further influence from the axial field is required for the instability to grow.

Scaling magnetized liner inertial fusion on Z and future pulsed-power accelerators

“…As discussed above, the beryllium liners shown in red have an aspect ratio, A R ¼ R out /DR ¼ 6 for all simulations presented in this study. Numerical simulations 4 indicated and experiments [7][8][9][10][11] have confirmed that A R ¼ 6 liners should be sufficiently robust to the RT instability. These experiments were performed with drive currents of approximately 18 MA.…”

“…The fuel preheating and the magnetically inhibited radial conduction reduce the required volume compression and thus the convergence needed to achieve fusion temperatures. Numerical simulations and experiments 4,[7][8][9][10][11] indicate thick walled liners with an aspect ratio (A R ¼ R outer /DR wall $ 6) should be adequately robust. Larger aspect ratios may be possible with the suppression of the electro-thermal instability, 12 but we use the conservative value A R ¼ 6 for this study.…”

Coupling of sausage, kink, and magneto-Rayleigh-Taylor instabilities in a cylindrical liner

“…[2][3][4][15][16][17][18] Without an axial magnetic field, MRT structure is typically oriented along nearly horizontal planes perpendicular to the z-axis with limited or no pitch. 12,13 However, with the inclusion of an axial magnetic field, helical structures were found with significant inclination during the implosion phase. 12,13 In the fully integrated MagLIF experiments (with axial magnetic field and a preheated fuel in the central region inside the liner), possible kink-like perturbations of the plasma column were reported at stagnation.…”

“…12,13 However, with the inclusion of an axial magnetic field, helical structures were found with significant inclination during the implosion phase. 12,13 In the fully integrated MagLIF experiments (with axial magnetic field and a preheated fuel in the central region inside the liner), possible kink-like perturbations of the plasma column were reported at stagnation. 14 These non-axisymmetric MHD activities are yet to be explained.…”

“…[4][5][6][7] They have become an important issue in the recent magnetized liner inertial fusion (MagLIF) experiments [8][9][10][11][12][13][14] on the Z-machine at Sandia National Laboratories. While there have been extensive studies of MRT on the MagLIF liner without an axial magnetic field, [9][10][11] many of these MRT theories were based on a slab geometry which is incapable of describing the conventional sausage mode and kink mode.…”