Fusion by laser-driven flame propagation in solid DT-targets

Abstract

When a laser light flux ϕ impinges on a solid target a radiation wave propagates which transforms the material into a hot plasma. The structure of the hot parts is known to show an overdense hot stationary deflagration structure followed by a nearly isothermal rarefaction. The temperature T of the hot plasma varies as (ϕ/nec)2/3, nec being the cut-off density. Then the ratio of the energy of the thermonuclear reaction products to the sum of the radiated energy plus the (kinetic + thermal) energy in the plasma is readily calculated for DT as a function of the duration of the interaction. For a 30% efficiency of the energy-conversion cycle, typical figures for a positive energy balance are ϕ = 5 × 1014W/cm2 (T = 108 °K), τ = 10−7 s for Nd glass, and ϕ = 5 × 1012W/cm2 (T = 108°K), τ = 10−5 s for CO2 laser. For both cases, the required laser energy density is a few 107 joules/cm2. In the latter case, a megagauss confining field could be successfully used to maintain a one-dimensional flame-propagation geometry.