Measurements of the spatial magnetic field distribution in a z-pinch plasma throughout the stagnation process

Abstract

We report on measurements, made for the first time for an imploding plasma at its stagnation, of the magnetic field spatial distribution. Utilized for the measurements is a spectroscopic technique based on simultaneous recording of each of the left-and right-handed circularly polarized Zeeman emissions. While this method allows for overcoming the Stark-and Doppler-broadenings that obscure the Zeeman splitting, it requires a line of sight that is parallel to the magnetic field lines. To this end, the radial charge-state distribution in the stagnating z-pinch plasma was measured, and the method was employed for emission lines of several selected charge states located in various radial locations. This also allowed for measuring the time-resolved magnetic field radial distribution in a single discharge, which is advantageous for high-energy-density plasma experiments. These distributions were measured at various locations along the pinch axis. K : Plasma diagnostics-charged-particle spectroscopy; Plasma diagnostics-high speed photography; Plasma diagnostics-interferometry, spectroscopy and imaging 1Corresponding author.

Observation of fast current redistribution in an imploding plasma column

“…Specifically, we measure that during stagnation the current transitions out of the SP and into a low density plasma (LDP), residing at much larger radii, while the SP continues to implode. This phenomenon might be connected to the previous observations of low current in the SP of Zpinches [11,20,[24][25][26], and might be common to various pulsed-power systems, including those of lower density plasmas [11], such as plasma switches [12][13][14] and high power transmission lines [15,16].…”

“…A few experimental studies have measured the timedependent magnetic field radial distribution in the imploding Z-pinch plasma [22][23][24][25]; those that were performed at the time of stagnation [24][25][26], outside the SP but close enough to it, confirmed the flow of only a small fraction of the current in this plasma. However, in the present work, the temporal evolution of the current density radial distribution was determined down to the small radius of the SP and, in particular, with a high spatial resolution.…”

“…The experimental system used an initial gas column with a radial distribution that provided a peak density on axis, thus allowing for satisfactory reproducibility and symmetry due to the mitigation of the Magneto-Rayleigh-Taylor instabilities [27,28]. The diagnostics, based on Zeemanpolarization spectroscopy, allowed for determining B θ , even when the Zeeman-split pattern was fully obscured by the line broadening [22][23][24][25]29]. Also, the radial distribution of charge states in the plasma was measured, as in [22,24,25], and was used to obtain B θ as a function of r from the chordal measurements without the need to inverse Abel transform the observed line shapes (i.e.…”

Effects of a Preembedded Axial Magnetic Field on the Current Distribution in a Z -Pinch Implosion

“…However, reliable experimental data on the B-field distribution in Z-pinches are scarce due to the high electron densities, high ion velocities, and transient nature of the plasma, which make measurements of B-fields in such plasmas rather difficult. We note a few examples of such spectroscopic measurements in gas-puff Z-pinches [22][23][24], and measurements based on Faraday rotation in wire-array Z-pinches [25].…”

“…Here, we present an experimental determination of B θ throughout the magnetized plasma implosion, achieved using a noninvasive spectroscopic technique that provides a high sensitivity for the Zeeman effect [26]. This technique is based on the polarization properties of the Zeeman components for light emission viewed parallel to the B-field, as described in [27][28][29][30], and recently implemented for Z-pinch implosions [24]. These measurements showed that the application of an initial axial magnetic field (B z0 ) has a significant effect on the current distribution in the plasma: a large part of the current does not flow in the imploding plasma, rather it flows through a low-density plasma (LDP) residing at large radii (here, by "current distribution" we mean the partition of the total current between the flow in the imploding plasma and the LDP).…”