Temperature and Density Measurements of an Optically Thick, Dense Aluminum Plasma Heated by Monochromatic Electrons

Temperature and density measurements of range-thin pure aluminum foils heated by an intense, relativistic, monochromatic electron beam have been performed for the first time. Electron density measurements are obtained from a 532-nm air-wedge shearing interferometer and indicate a large, long-lived volume of dense plasma. The plasma grows to extend more than 5 mm off the target face, and lasts more than 500 ns from the initial deposition of energy. Spatially-and temporally-resolved visible spectroscopy normal to the target foil provides a complimentary diagnostic of the plasma plume temperature and density. The spectrometer measures the Al-I 3p–4s resonance lines, which were consistently observed to be optically thick. Stark broadening of the Al-I doublet, after correcting for self-absorption effects, yields electron densities >4x10 17 cm -3 and electron temperatures around 1 eV. Initial atomic kinetics calculations are presented to threshold plasma temperatures based on the Al-I line profiles. A spectroscopic-quality radiation transport model is developed to post-process results of a radiation-hydrodynamics simulation of the energy deposition and subsequent hydrodynamic expansion of the plasma, including estimating the optical depth of the Al-I lines.