ENERGETICS AND SYMMETRY OF HOHLRAUM TARGETS DRIVEN BY ION-BEAM PULSESWITH SIMPLE TIME SHAPE

The energetics of hohlraum targets for inertial fusion are studied by means of one-dimensional radiation hydrodynamics simulations, assuming that a pulse of thermal X-rays with a simple time shape is fed into t he cavity. A fusion yield E(fus) = 160-250 MJ is released by a capsule with fuel mass m(DT) = 3.3 mg, driven by a two-step pulse. The requir ed input energy is E(x) approximate to 3.4 MJ for a hohlraum area rati o a = 9 and 6.6 MJ for a = 20, corresponding to gains of G(x) = E(fus) /E(x) = 50-73 and 25-35 respectively. Higher gains are obtained by thr ee-step pulses. Targets with m(DT) = 0.4 mg require better-shaped puls es, with at least three steps. Driven by E(x) = 0.85-1.7 MJ, they rele ase E(fus) = 8-10 MJ. Symmetry aspects of axially symmetric hohlraums driven by heavy ion beams are studied by a viewfactor code, employing wall motion and re-emissivities provided by the one-dimensional hydro- simulations. The dependence of the capsule irradiation asymmetry on th e hohlraum aspect ratio, area ratio and fill density is analyzed. Redu ctions of wall motion and converter expansion, and the use of shields appear necessary to allow for the use of a moderate area ratio alpha a pproximate to 10-15.