Wall ablation, gas dynamics, and the history of wall stresses in ICF target chambers

Calculations of the history of wall stresses for spherical aluminum laboratory microfusion facility (LMF)-type inertial confinement fusion (ICF) target chambers 10-cm thick with 1400-MJ pellets are made using a simple computer program called CHAMBER. The program incorporates the physics of first-wall ablation and chamber-gas dynamics, including dissociation, ionization, and gas reverberations. By considering the time dependence of the wall stresses, the author calculates peak stresses that are higher or lower than previous estimates based on the dynamic formula σ_dyn≈PR/ΔR, depending on the radius of the chamber. P is the interior pressure, R is the chamber radius, and ΔR is the wall thickness. In particular, the previous estimates are too small for chambers with radii R>4 m or R<0.5 m because the ablation impulse dominates the stress for R>0.5 m. CHAMBER also shows that considerably more wall mass can be ablated after the X-ray-vaporized mass fills the chamber if the thermalized vapor radiates more energy to the wall than the wall can conduct away by heat conduction (as in small chambers). Venting of a chamber can reduce the wall stress only to that caused by the ablation impulse, and only for vents with radii comparable to the radius of the chamber