Shock ignition of direct-drive double-shell targets

Shock ignition is investigated for non-cryogenic direct-drive double-shell targets. The fuel assembly is obtained by direct laser light absorbed in the external shell. The latter implodes and impacts the inner shell. The ignition is produced by a spherically convergent shock launched by a laser spike added at the end of the main laser drive. Analyses are carried out with and without a correction for the fuel assembly laser pulse. The correction is made by lowering the assembling laser pulse in order to maintain the implosion velocity constant when the ignitor spike is added. The results indicate that a moderate thermonuclear gain (similar to 2 for spike power in the range 100-250 TW) can be achieved while the ignition threshold is displaced towards lower laser energies. The thermonuclear yield is tuned by the power in the spike which is a free parameter. A better gain is obtained when the main drive laser pulse is not corrected due to the dual effect of the increases in implosion velocity and in the DT ion temperature when the ignitor shock collapses.