Speaker
Description
Thomson scattering measurements have been performed on plasma jets created from a 15 µm thick radial Al foil load on COBRA, a 1 MA pulsed power machine. Two different spectrometers were used to collect both the ion acoustic wave (IAW) and the electron plasma wave (EPW) spectral features. The IAW feature gives a good measurement of the electron temperature, while the EPW feature measures the electron density. The laser used for Thomson scattering had an energy of 10 J at 526.5 nm and a 2.2 ns full width at half maximum duration. The IAW feature was recorded with a streak camera for time resolution of the scattering, while the EPW feature was integrated over the entire laser pulse but had spatial resolution. This Thomson scattering system was used to compare plasma conditions in the jets under different current polarities. Previous experiments and computer simulations showed that the direction of the current can significantly affect jet properties due to extended magnetohydrodynamic effects such as the Hall effect. Experiments show that around peak current, jets with current flowing radially outward (“reverse polarity”) through the foil were taller and denser than jets with current flowing radially inward (“standard polarity”). This caused reverse polarity jets to be heated from 20 to 40 eV from inverse bremsstrahlung by the probing laser, while standard polarity jets stayed relatively constant at 20 eV. The EPW feature measures densities outside of the jet to be around $5\times10^{17}$ cm$^{-3}$ while inside the jet the density was at least $2\times10^{18}$ cm$^{-3}$. In addition, the widths of the Thomson scattering peaks will be discussed, as they can give either information on the temperature of the plasma or other plasma properties.
Work supported by the NNSA Stewardship Science Academic Program under DOE Cooperative Agreement - DE-NA0003764.
