Abstract
We present the first experimental measurement of temperature and density of a warm dense plasma produced by a pulsed power driver at the Nevada Terawatt Facility (NTF). In the early phases of discharge, most of the mass remains in the core, and it has been challenging to diagnose with traditional methods, e.g. optical probing, because of the high density and low temperature. Accurate knowledge of the transport coefficients as well as the thermodynamic state of the plasma is important to precisely test or develop theoretical models. Here, we have used spectrally resolved non-collective X-ray Thomson scattering to characterize the dense core region. We used a graphite load driven by the Zebra current generator (0.6 MA in 200 ns rise time) and the Ti He-α line produced by irradiating a Ti target with the Leopard laser (30 J, 0.8 ns) as an X-ray probing source. Using this configuration, we obtained a signal-to-noise ratio ~2.5 for the scattered signal. By fitting the experimental data with predicted spectra, we measured T = 2±1.9 eV, ρ = 0.6±0.5 gr/cc, 70 ns into the current pulse. The complexity of the dense core is revealed by the electrons in the dense core that are found to be degenerate and weakly coupled, while the ions remain highly coupled.
Highlights
High Energy Density (HED) plasmas are frequently produced in pulsed power systems either by plasma compression using the intense Lorentz force (JXB) or when the plasma starts from solid, metallic materials where the phase state of the material changes from Warm Dense Matter (WDM) up to a plasma state as the current Ohmically heats the material[1]
Only a few facilities in the world exist that couple a high-intensity laser to a pulsed power driver, limiting the implementation of this technique on pulsed power facilities. One such facility is Sandia National Laboratories, where in a recent work on the Z pulsed power generator, space-resolved X-ray Thomson scattering from shocked carbon foams was accomplished[14]
The goal of the work was to enable the advances of WDM physics by combining the powerful X-ray Thomson scattering (XRTS) diagnostic with the extreme environment created at the Sandia Z pulsed power accelerator
Summary
High Energy Density (HED) plasmas are frequently produced in pulsed power systems either by plasma compression using the intense Lorentz force (JXB) or when the plasma starts from solid, metallic materials (such as wire arrays or liners) where the phase state of the material changes from Warm Dense Matter (WDM) up to a plasma state as the current Ohmically heats the material[1]. Only a few facilities in the world exist that couple a high-intensity laser to a pulsed power driver, limiting the implementation of this technique on pulsed power facilities One such facility is Sandia National Laboratories, where in a recent work on the Z pulsed power generator, space-resolved X-ray Thomson scattering from shocked carbon foams was accomplished[14]. The goal of the work was to enable the advances of WDM physics by combining the powerful XRTS diagnostic with the extreme environment created at the Sandia Z pulsed power accelerator Another Facility capable of coupling a high intensity laser to a pulsed power generator is the Nevada Terawatt Facility (NTF), where the work presented here was carried out. The scattering wave vector k in the non-relativistic limit (or small momentum transfer) is defined as: k
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