Nonequilibrium hydro-burn simulations of early laser-driven-compression experiments indicate that low-energy photons from the vicinity of the ablation surface are preheating the microballoon pushers, thereby severely limiting the compression achieved (similar degradation may result from 1-4% energy deposition by superthermal electrons). This implies an 8- to 27-fold increase in the energy requirements for breakeven, unless radiative preheat can be drastically reduced by, say, the use of composite ablator pushers.

• Received 2 June 1975

DOI:https://doi.org/10.1103/PhysRevLett.35.520