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%.
Preliminary target design for integrated direct-drive fast ignition experiments on Shenguang-II upgrade facility
