Numerical analysis of the direct drive illumination uniformity for the Laser MegaJoule facility

• Published in: Physics of plasmas 2014-01, Vol.21 (1)
• Main Authors: Temporal, M., Canaud, B., Garbett, W. J., Ramis, R.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; BEAMS; CAPSULES; Cones; Gaussian beams (optics); ILLUMINANCE; Illumination; INERTIAL CONFINEMENT; Inertial confinement fusion; IRRADIATION; Laser beams; LASERS; NUMERICAL ANALYSIS; Plasma physics; POSITIONING; SPHERICAL CONFIGURATION
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.4863460

The illumination uniformity provided during the initial imprinting phase of the laser foot pulse in a direct drive scenario at the Laser MegaJoule facility has been analyzed. This study analyzes the quality of the illumination of a spherical capsule and concerns the uniformity of the first shock generate in the absorber of an Inertial Confinement Fusion capsule. Four configurations making use of all or some of the 80 laser beams organized in the 20 quads of the cones at 49° and 131° with respect to the polar axis have been considered in order to assemble the foot pulse. Elliptical and circular super-gaussian laser intensity profiles taking into account beam-to-beam power imbalance (10%), pointing error (50 μm), and target positioning (20 μm) have been considered. It has been found that the use of the Polar Direct Drive technique can in some cases reduce the irradiation non-uniformity by a factor as high as 50%. In all cases, elliptical profile provides better results in comparison with the circular one and it is shown that the minimum of the non-uniformity is also a function of the capsule radius.