Optimizing design of irradiation uniformity of direct drive cone-in-shell target for fast ignition

Abstract

The irradiation uniformity of a cone-in-shell target directly driven by laser beams has been considered. First, a model is established to include the influence of the cone on laser beam propagation. Then, the irradiation uniformity on the target surface outside the cone during the initial imprinting phase is analyzed, and highly uniform irradiation on the target surface outside the cone is achieved by optimizing the intensity distribution within laser beams, as well as the polar direct drive displacement. As an illustrative example, direct drive irradiation uniformity of a typical cone-in-shell target is improved for Shenguang III laser facility, the illumination non-uniformity is reduced from 5.8% to 1.1%. Irradiation on the cone surface outside the target is also analyzed, and it is found that for the laser-target configuration considered in this work, a gold cone thicker than 50μm is needed to avoid shock breakout. Moreover, sensitivity to beam uncertainties (power imbalance and pointing error) is analyzed, indicating that this scheme can tolerate a certain amount of beam errors.