Low initial aspect-ratio direct-drive target designs for shock- or self-ignition in the context of the laser Megajoule

Abstract

Analysis of low initial aspect ratio direct-drive target designs is carried out by varying the implosion velocity and the fuel mass. Starting from two different spherical targets with a given 300 /xg-DT mass, optimization of laser pulse and drive power allows to obtain a set of target seeds referenced by their peak implosion velocities and initial aspect ratio (A = 3 and A = 5). Self-ignition is achieved with higher implosion velocity for A = 5-design than for A = 3-design. Then, rescaling is done to extend the set of designs to a huge amount of mass, peak kinetic energies and peak areal densities. Self-ignition kinetic energy threshold Ek is characterized by a dependance of Ek ~ v& with ^S-values which depart from self-ignition models. Nevertheless, self-ignition energy is seen lower for smaller initial aspect ratio. An analysis of Two-Plasmons Decay threshold and Rayleigh-Taylor instability e-folding is carried out and it is shown that two-plasmon decay threshold is always overpassed for all designs. The hydrodynamic stability analysis is performed by embedded models to deal with linear and non-linear regime. It is found that the A = 5-designs are always at the limit of disruption of the shell.

Influence of laser induced hot electrons on the threshold for shock ignition of fusion reactions

“…Among known SI designs 4,25,[32][33][34][35][36] , two targets are considered: (i) the baseline pure-DT target proposed in the original HiPER project in Ref. 25 and (ii) an advanced design with increased gains and robustness to hydrodynamic instabilities, proposed in the Celia laboratory.…”

Effect of ‘wandering’ and other features of energy transfer by fast electrons in a direct-drive inertial confinement fusion target

“…The adjustment of the parameters of such a target and laser pulse ensures achievement of maximal shell velocity up to the values of 400 km/s and evaporation of the most part of ablator (75-90% of its mass) at the DT-shell aspect ratio not exceeding 5-10. The initial parameters and implosion characteristics of this kind of targets, discussed in various laboratories [1,10,11], differ slightly from each other. Therefore, the features of the kinetics of fast electrons in such targets have a general nature.…”

“…The initial parameters and implosion characteristics of this kind of targets, discussed in various laboratories [1,10,11], differ slightly from each other. Therefore, the features of the kinetics of fast electrons in such targets have a general nature.…”

Irradiation uniformity at the Laser MegaJoule facility in the context of the shock ignition scheme

“…The cryogenic nuclear fuel is surrounded by a thin ( ) shell of plastic ( devoted to the laser energy absorption. Detailed parametric studies have been performed showing that the self-ignition threshold in the implosion velocity is about [53] and that the maximum energy gain is with an incident energy of about 500 kJ and laser peak power of 230 TW [54] . In the considered LMJ design, the available energy (1.3 MJ) is above that needed by the capsule, which means we retain some energy margin against constraints mainly related to the required irradiation uniformity.…”