Time Evolution of the Pinch Region of a Deflagration Plasma Accelerator

A spectroscopic study of a plasma deflagration accelerator was carried out to investigate the temporal evolution of plasma density within the pinch region. A half-meter imaging monochromator, paired with a fast (10 MHz) camera operating at 1 MHz, was used to collect broadened chord-integrated spectral lines from the pinch region of a plasma deflagration device. Specifically, images of the $H_{\beta}$ and the $H_{\alpha}$ lines were taken - with the $H_{\alpha}$ used to find the background continuum. Voigt fits of the Abel inverted H$_{\beta}$ emission lines allowed for determination of the radial profile of the number density in the pinch at intervals of 1 $\mu$s. This provided insight into the formation, growth, and decay of the pinch in both the deflagration and detonation modes of the accelerator. It was found that the maximum density for the deflagration increased from $\sim 10^{20}$ m$^{-3}$ 1.4 cm away from the core of the pinch to $\sim 10^{23}$ m$^{-3}$ at the core of the deflagration pinch. In contrast, the detonation pinch featured a broader zone of relatively constant density on the order of $\sim 10^{20}$ m$^{-3}$. Furthermore, an energy balance of the plasma in the deflagration pinch and downstream, as informed by prior work, was done to get an estimate of temperatures in the core of the pinch where measurements are not currently possible revealing potential temperatures on the 550 eV in the core of the pinch suggesting departures from some of the assumptions in the analysis.