Observations of the Effect of Ionization-Potential Depression in Hot Dense Plasma

Abstract

The newly commissioned Orion laser system has been used to study dense plasmas created by a combination of short pulse laser heating and compression by laser driven shocks. Thus the plasma density was systematically varied between 1 and 10 g/cc by using aluminum samples buried in plastic foils or diamond sheets. The aluminum was heated to electron temperatures between 500 and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. The K-shell spectra show the effect of the ionization potential depression as a function of density. The data are compared to simulated spectra which account for the change in the ionization potential by the commonly used Stewart and Pyatt prescription and an alternative due to Ecker and Kröll suggested by recent x-ray free-electron laser experiments. The experimental data are in closer agreement with simulations using the model of Stewart and Pyatt.

Energy Penetration into Arrays of Aligned Nanowires Irradiated with Relativistic Intensities: Scaling to Terabar Pressures

“…Simulations indicate a pressure of 0.5 Gbar, and an energy density approaching 1 × 10 8 J cm −3 was obtained. Similar temperatures were achieved at a density of 9 g/cc, and therefore higher pressure and energy density, using diamond tamped Al targets compressed with a pair of 200-J, long laser pulses before the arrival of the short heating pulse (10). Several other experiments in which pulses of 0.35-to 2-ps duration irradiated plastic foils with buried metal layers reported similar temperatures (11)(12)(13)(14).…”

“…Heating by hot electrons using today's most energetic short pulse lasers has just surpassed the boundary into the UHED regime (for example, achieving 2 Gbar). For example, temperatures of 0.6 keV at a density of 1.5 g/cc were recently reported for a 0.15-mm-thick Al foil tamped by 10 mm of plastic on both sides, irradiated by 100-J pulses of 0.5-ps duration (10). Simulations indicate a pressure of 0.5 Gbar, and an energy density approaching 1 × 10 8 J cm −3 was obtained.…”

Density functional theory calculations of continuum lowering in strongly coupled plasmas

“…More recently, Hoarty et al 15 have constrained the possible values of the IPD in Al plasmas heated to temperatures in excess of 500 eV, and over a range of ion densities, using very thin Al foils embedded in plastic or diamond, compressed and heated by the Orion laser at AWE. Their results agree qualitatively with the predictions of SP, and are inconsistent with the EK model for the temperatures and densities they quote to have reached.…”

“…Their results agree qualitatively with the predictions of SP, and are inconsistent with the EK model for the temperatures and densities they quote to have reached. Bearing in mind that although the LCLS and AWE experiments were conducted in moderately different plasma coupling conditions, the two models still remain mutually incompatible 12,15 , and the large continuum lowering observed in the LCLS experiments has proven challenging to explain with existing models.…”

A study of density effects in plasmas using analytical approximations for the self-consistent potential

“…This interest has been revived recently by the availability of lineshift measurements in dense plasma emission [2,3]. The description of such effects is complex since it implies the elaboration of a quantum theory of a very large system.…”