Progress in direct-drive fusion studies for the Laser Mégajoule

Abstract

In the context of the French Laser Mégajoule (LMJ) fusion research program, direct drive is an alternate to indirect drive to reach ignition and thermonuclear burn. We present recent progress in the direct-drive fusion studies for LMJ. Calculations have shown that the LMJ irradiation uniformity is characterized by long wavelength asymmetries compatible with direct drive requirements. Calculations of the irradiation uniformity in the context of indirect drive beam positioning have been done. We show that non-uniformity can be minimized by repointing the beams. Unfortunately, a time analysis shows that this nonuniformity increases strongly in time above levels usually considered inconsistent for direct drive. Finally, a recent baseline target design is presented and consists of a DT ice shell surrounded by a low-density CH foam wicked with cryogenic DT. This design can potentially reach a gain of 90 with a 1-MJ on-target laser driver. Hydrodynamic stability is increased at the ablation front and the laser–target coupling efficiency achieves 85%.