Heat waves and ionization fronts

Summary form only given. In the literature regarding the penetration of energy into matter in experiments at high energy density, one often encounters discussions of “Marshak waves”, or of “ionization fronts” or sometimes of “heat waves” or “heat fronts”. Looking a bit deeper, one finds that these terms are used rather inconsistently. In addition, many of the papers refer to connections with similar phenomena in astrophysics, but there is rarely any discussion of how the experiment actually connects with real astrophysical cases. We believe that better experiments, and better papers, would result from attention to the fundamental mechanisms at work in these phenomena, and to how one might use language to draw relevant distinctions among cases. In addition, an examination of similarities and differences with actual astrophysical cases ought to offer some further clarity. In this presentation we will begin with a discussion of these fundamental mechanisms, and consideration of the circumstances under which they each are dominant. We will proceed toward a unified discussion of the laboratory and astrophysical phenomena within this general category of penetration of energy.