Magneto-Rayleigh-Taylor instabiliity mitigation in multi-species gas-puff Z-pinches*

The gas-puff Z-pinch is a well-known, efficient source of X-rays and/or neutrons, in which an axially applied current interacts with the azimuthal self-magnetic field to drive a radial implosion. It is highly susceptible to the magneto-Rayleigh-Taylor instability (MRTI), which can disrupt the pinch if unmitigated.  Axial pre-magnetization can mitigate MRTI growth but tends to reduce yield [1] as the initial field, B_z0, is increased. Here, we present 2-D magnetohydrodynamic simulations [2] of Ne-liner, deuterium-target gas-puff loads driven by an 850 kA, 160 ns driver which show that the tradeoff between stability and yield can be reduced by adding a second liner. A B_z0 of 0.7 T is required to stabilize the single-liner implosion with initial radius 2.5 cm, but thermonuclear neutron yield decreases from 1.2x10⁹ with B_z0 = 0 T to 1.0x10⁷ with B_z0 = 0.7 T. When a second liner is added with radius 1.25 cm, the required B_z0 is reduced to 0.3 T. Consequently, the penalty to yield is significantly reduced: from 1.2x10⁹ with B_z0 = 0 T to 9.8x10⁸ with B_z0 = 0.3 T. We show this concept scales favorably with current to 10 MA, at which level thermonuclear yields of ~10¹³ are predicted.

[1] F. Conti et al., Phys. Plasmas 27, 012702 (2020).

[2] J. Narkis et al., Phys. Rev. E (under review).