The open-quotes laser greenhouseclose quotes thermonuclear target with distributed absorption of laser energy

We propose a new type of target for laser-driven thermonuclear fusion, which can ensure uniformity in the distribution of laser energy absorbed by the target and thus uniformity in the pressure required to compress the thermonuclear material (fuel). A distinctive component of this target is a special absorber of laser radiation placed between an external inertial shell and an internal spherical capsule that contains the thermonuclear material. Laser radiation is introduced into the absorber through apertures in the external shell. The absorber consists of low-density material (e.g., a porous material or gas) made up of light elements with a density lower than the critical density of the plasma formed by the laser. The distribution of absorbed energy is equalized by propagation of supersonic electron thermal conduction waves as distributed inverse-bremsstrahlung absorption of the laser radiation takes place in the subcritical plasma of the absorber. Our theoretical studies have shown that for a target with a high thermonuclear gain coefficient G ≥ 1, thermal equalization of nonuniformities in the plasma heating is possible even when a laser with as few as six beams is used. The target we propose has excellent energy characteristics: one-dimensional numerical calculations show that the threshold value of laser energy for the ignition of this type of target is 100-200 kJ, i.e., considerably smaller than that required for indirect drive. Moreover, calculations show that the gain coefficient increases rapidly for this type of target with increasing laser energy. Thus, for a laser energy of 1 MJ the amplification coefficient is approximately equal to 50. 24 refs., 5 figs