Magnetic Field Compression in ICF and its Effects on Thermal Conduction and Alpha Heating

Typical inertial confinement fusion (ICF) implosions lose energy and temperature from the central hot spot by thermal, radiative, and fusion-product (alpha-particle) losses. Applying a magnetic field to these hotspots can help trap the charged particles and insulate against thermal losses and alpha-particle escape into the cold fuel reservoir. However, one outstanding issue that complicates our theoretical understanding is that both the thermal and alpha-particle insulation are sensitive to the magnetic field topology and to the temperature profiles (which are themselves sensitive to the magnetic field topology). In this work, we develop a comprehensive model for magnetized hotspots, including (1) how do fields compress spherically, (2) how do the resulting magnetic (rotational) discontinuities evolve, (3) what is the magnetized temperature profile, and (4) what is the overall effect on thermal and alpha-particle insulation. This model explains the intricate magnetic field and temperature profiles observed in radiation-magnetohydrodynamics simulations, as well as providing a framework to develop magnetized ignition criteria and hotspot models. We show that magnetothermal insulation is maximized for highly compressive implosions, providing a future design goal in the optimization of magnetized igniting ICF targets.