A method to probe Rosseland and Planck mean opacities with high-order harmonics

Abstract

An experimental method to measure frequency-averaged Rosseland and Planck mean opacities is presented. We propose using high-order harmonics (HHG) from a laser-plasma source to probe plasma opacities at multiple photon energies enabling the determination of accurate values of the frequency-averaged opacities. The requirements for the number of harmonic sets, maximum photon energy and laser line width are investigated. Additionally, effects of experimental errors such as transmission measurements, plasma uniformity and temperature diagnostics on the accuracy of the probed mean opacity values are discussed. Assuming temperatures are measured to 10% accuracy, we show that it is possible to measure directly Rosseland and Planck mean opacities with an accuracy of approximately 20% using HHG probing. We show that the accuracy of the HHG technique, and most other opacity probing techniques, is primarily determined by the accuracy of the measurement of plasma temperature. The experimental opacity data that can be obtained in this way will enable a direct measure of the Rosseland and Planck opacities for use in simulations of relevance to high energy density matter, particularly inertial fusion and astrophysics.