Investigating magnetised, radiatively driven plasmas with a university scale pulsed-power generator *

We present first results from a novel experimental platform which is able to access physics relevant to topics including indirect-drive ICF, MAGLIF, and laboratory astrophysics (for example the penetration of B-fields into HED plasmas).

This platform uses the X-Rays from a wire array Z-Pinch to irradiate a solid target, producing an outflow of ablated plasma. Target materials include silicon, aluminium, and polycarbonate. The ablated plasma expands into ambient, dynamically significant B-fields (∽ 10 T) which are supported by the current flowing through the Z-Pinch. The outflows have a well-defined (quasi-2D) morphology, enabling the study of fundamental processes typically only available in more complex, integrated schemes.  

Experiments were fielded on the MAGPIE generator (1.4 MA, 240 ns). On this machine a wire array Z-Pinch produces an X-Ray pulse carrying a total energy of  ∽15 kJ over ∽30 ns.

A suite of spatially resolved diagnostics including interferometry, Thomson scattering, and Faraday rotation were used to characterise plasma conditions. These have enabled the measurement of electron density, plasma temperature, average ionisation, flow velocity, drift velocity, and B-field. Electron densities lie in the range 10¹⁷ – 10¹⁸  cm^-3, and temperatures are typically ∽10  eV.

Results have been compared to rad-hydro and atomic codes including Chimera, HeliosCR, FLYCHK, and IMP.  When considering B- field, our comparisons indicated that resistive-MHD predicts a more diffusive profile than was observed in experiment. When considering ionisation, we found a collisional-radiative approach under-predicts the average charge state seen in experiments.

The platform will also allow the direct measurement of charge state distribution (with absorption spectroscopy), and the comparison of expansion for plasmas flowing parallel/perpendicular to the B-field.