Spectroscopic Measurement of High-Frequency Electric Fields in the Interaction of Explosive Debris Plasma with Ambient, Magnetized Background Plasma

The explosive expansion of dense, high-beta debris plasma into relatively tenuous, magnetized background plasma is relevant to a wide variety of astrophysical and space environments. Electric fields play a fundamental role in the coupling of momentum and energy from debris to background, and emission spectroscopy provides a powerful diagnostic for assessing electric fields via the Stark effect. A recent experiment utilizing a unique experimental platform at UCLA that combines the Large Plasma Device and the Raptor laser facility has investigated the super-Alfv\'enic, quasi-perpendicular expansion of a laser-produced carbon (C) debris plasma through a preformed, ambient, magnetized helium (He) background plasma via emission spectroscopy. Spectral profiles of the He II 468.6 nm line have been analyzed via single-mode and multi-mode time-dependent Stark broadening models for hydrogen-like ions, yielding large magnitude ($\sim$100 kV/cm), high-frequency ($\sim$100 GHz) electric fields. The measurements suggest the development of an electron beam-plasma instability, and a simple instability saturation model demonstrates that the measured electric field magnitudes are feasible under the experimental conditions.