The physics of hot, dense plasmas is a field rich with physics and mathematics, spanning many different length and time scales. To accurately simulate hot, dense plasmas requires resolving the physics of hydrodynamics, radiation and electron transport, atomic physics, burn physics, wave-wave interactions, wave-particle interactions and particle-particle interactions, to name a few processes.
To perform such a calculation that resolves such physics at all these length and time scales remains computationally unfeasible even with an exascale capability. Thus, it is important to differentiate between the physics that must be fully resolved, and the physics that can be included with a reduced model description in a fully integrated simulation. These fully integrated simulations including reduced model descriptions can then be validated through experiment.
A key example of such a computational problem is modeling support for the National Ignition Campaign (NIC). NIC seeks to demonstrate fusion in the laboratory via inertial confinement fusion. In this process, the National Ignition Facility (NIF) laser is incident upon a cylinder composed of gold, or other high-Z materials. The laser is converted to x-radiation at the cylinder walls, and bathes the cylinder interior with radiation. In the center of the cylinder is a pellet, composed of heavy hydrogen (deuterim + tritium). The radiation oven created within the cylinder bathes this pellet and compresses it to conditions where D and T atoms fuse, emitting a He nucleus and an energetic (14.6 MeV) neutron.
The story of the interplay among the length and time scales of this challenging scientific endeavor occurs in many different ways in modeling such an experiment. Here, the example of laser energy coupling to the cylinder is used to demonstrate the key challenges and deficiencies in computations of hot, dense plasmas.