A two-temperature thermonuclear burn condition for inertial confinement fusion targets with high-Z pushers

Two-temperature threshold conditions for the onset of thermonuclear (TN) self-heating and robust volume-burn in optically-thin plasma surrounded by a high-Z (opaque) pusher are presented. Volume-ignition ICF target designs employing high-Z metal pushers aim to minimize radiative plasma cooling by “trapping” bremsstrahlung radiation inside the fusion fuel cavity, lowering the required fuel energy for the onset of TN burn and ignition.[1] Traditional treatments have assumed that the onset of TN burn occurs while the plasma and radiation are in thermal equilibrium. However, simulations consistently suggest that this is not guaranteed. Here, a multi-fluid plasma model is used to derive threshold conditions for the onset of TN burn, where thermal equilibrium between the plasma and radiation at the initiation of TN self-heating is not assumed, and coupling between photons and electrons is retained.  Additionally, the role of the thermodynamic evolution of the pusher, specifically the time-evolution of the pusher-wall temperature, in regulating the power-balance in the plasma and the time-dependent evolution of the self-heating threshold is discussed.

 

[1] Peter Amendt et al., Phys. Plasmas 9, 2221 (2002); Kim Molvig et al., Phys. Rev. Lett. 116, 255003 (2016); D. S. Montgomery et al., Phys. Plasmas 25, 092706 (2018)