Direct-drive laser fusion: Status and prospects

Abstract

Techniques have been developed to improve the unifoimity of the laser focal profile, to reduce the ablative Rayleigh-Taylor &stability, and to suppress the various laser-plasma instabilities. There are now three diiectdrive ignition target designs that utilize these techniques. Evaluation of these designs is still ongoing. Some of them may achieve the gains above 100 that are necessary for a fusion reactor. Two laser systems have been proposed that niay meet all of the requirements for a fusion reactor.

Effects of Nonuniform Illumination on Implosion Asymmetry in Direct-Drive Inertial Confinement Fusion

“…ρR asymmetry can be seen in sample D 3 He proton spectra from a single shot (25221), shown in Fig. 2.…”

“…Success requires a symmetric implosion, because significant deviation from spherical symmetry will result in shock dynamics that do not lead to ignition. In the direct-drive approach to ICF, where implosion occurs in response to a large number of high-power, individual laser beams illuminating the surface of a capsule, the requirement for spherical implosion imposes severe constraints on the uniformity of the laser drive [1][2][3] and on the sphericity of the capsule.…”

“…Attaining ignition and high gain in inertial confinement fusion (ICF) requires that deuterium-tritium (DT) filled capsules be spherically imploded to high temperature and density [1][2][3]. "Hot spot" ignition, where a capsule is compressed so as to form two different regions: a small mass of low density, hot (~10 keV) fuel at the center surrounded by a larger mass of high density, low temperature fuel, is the leading method envisioned to achieve this goal.…”

Laser performance of the SG-III laser facility

“…As essential drivers, several huge laser facilities have been constructed, such as the National Ignition Facility (NIF) in the United States [5] , the laser megajoule (LMJ) in France [6] and the SG-III laser facility in China [7] . These laser facilities are designed to provide timely tailored ultraviolet laser driving during as long as tens of nanoseconds, producing x-ray radiation in a hohlraum which then compresses DT pellet to achieve fusion ignition [4] . In order to deliver more energy onto the target, the lasers have to be converted to ultraviolet, and wavelength tuning is required to avoid energy loss.…”

“…As one of the major approaches to achieve controllable fusion ignition, laser driven inertial confinement fusion (ICF) has been widely studied around the world [1][2][3][4] . As essential drivers, several huge laser facilities have been constructed, such as the National Ignition Facility (NIF) in the United States [5] , the laser megajoule (LMJ) in France [6] and the SG-III laser facility in China [7] .…”