3D Dynamics of a Premagnetized Gas-puff Z-pinch implosion

Abstract

We present the first simultaneous, spatially-resolved measurement of all three velocity components (radial, azimuthal, and axial) in an annular magnetized argon gas-puff Z-pinch, performed using Collective Thomson Scattering along three orthogonal lines of sight from the same scattering volume at each time step. Measurements were carried out on the Llamp{ü}dke{ñ} pulse-power generator (400 kA peak, 200 ns rise time), for applied axial fields ranging from 0.04 to 0.26 T using two coil configurations: a double coil with negligible initial radial field at the probed plane ($z = 8$ mm), and a single coil that imposes a finite initial radial field. Three principal results are reported. First, the axial velocity component, which had not previously been measured experimentally in this configuration, reaches 60--70~km\,s$^{-1}$ near the axis at low applied fields ($B_{z0} < 0.1$ T) and is suppressed to within $\pm 20$~km\,s$^{-1}$ for stronger applied fields, in correlation with the reduction of the zippering angle, with direct implications for the implosion energy balance. Second, the self-generated rotation extends across the full plasma diameter, not only at the periphery, and the diametrical profile of the azimuthal velocity decreases toward the axis with an exponential-like shape consistent with the underlying current density distribution; this feature was not visible in previous edge-localized measurements. Third, rotation persists in the double-coil case ($B_{r0} \approx 0$) and is enhanced in the single-coil case (finite $B_{r0}$), supporting the interpretation that $B_r$ develops self-consistently during the implosion and drives the rotation through a $J_z \times B_r$ torque. These results constrain the role of each magnetic-field component and motivate direct measurement of $B_r$ and the current density distribution as the next step.