Isochoric heating of solid-density plasmas beyond keV temperature by fast thermal diffusion with relativistic picosecond laser light

Abstract

The interaction of relativistic short-pulse lasers with matter produces fast electrons with over megaampere currents, which supposedly heats a solid target isochorically and forms a hot dense plasma. In a picosecond timescale, however, thermal diffusion from hot preformed plasma turns out to be the dominant process of isochoric heating. We describe a heating process, fast thermal diffusion, launched from the preformed plasma heated resistively by the fast electron current. We demonstrate the fast thermal diffusion in the keV range in a solid density plasma by a series of one-dimensional particle-in-cell simulations. A theoretical model of the fast thermal diffusion is developed and we derive the diffusion speed as a function of the laser amplitude and target density. Under continuous laser irradiation, the diffusion front propagates at a constant speed in uniform plasma. Our model can provide a guideline for fast isochoric heating using future kilojoule petawatt lasers.

Heating in multi-layer targets at ultra-high intensity laser irradiation and the impact of density oscillation

“…There are several processes known to transfer energy from the laser to bulk temperature, e.g. isochoric heating by particle acceleration at the front surface [24][25][26], subsequent heat diffusion [26,27], shocks [28,29], or in the case of ultra-intense lasers also return current generation balancing the dense relativistic electron beam accelerated by the laser [17,[30][31][32]. The latter usually dominates the heating for short time scales (100 s fs) and has the advantage of relatively homogeneous heating through the target compared to diffusion or shocks.…”