A novel arrangement scheme of laser quads for spherical hohlraum in laser indirect-driven facility

Abstract

In traditional laser quads arrangement schemes for spherical hohlraum in indirect-driven laser facilities, the laser quads to bring about the laser entrance hole (LEH) to close when they are incident at a large angle (55), while the complicated cross and overlap of laser quads inside the spherical hohlraum may be generated when they are incident at a small angle (35). To overcome these problems, a novel laser quads arrangement scheme for spherical hohlraum is proposed. The laser quads injected into the single LEH are divided into two cones (the incident angle of the inner cone is 35, and that of the outer cone is 55). Furthermore, the contrast and the fractional power above the intensity have been proposed to evaluate the irradiation uniformity of single laser quad, while the dispersion degree and the duty ratio are proposed to evaluate the distribution uniformity of all laser quads on the spherical hohlraum wall. Based on the beam smoothing scheme implemented by the combination of one-dimensional smoothing by spectral dispersion, the continuous phase plate and polarization control plate, the propagation model of laser quads in the spherical hohlraum has been built up, and further used to analyze the irradiation uniformity of single laser quad and all the laser quads on the spherical hohlraum wall. On this basis, the irradiation characteristics on the LEHs and the spherical hohlraum wall, and the propagation characteristic of laser quads in the novel and traditional laser quads arrangement schemes have been analyzed and compared. Results indicate that, compared with the traditional arrangement scheme of laser quads, the novel laser quads arrangement scheme has following advantages: The irradiation uniformity on the spherical hohlraum wall of single laser quad and all laser quads remains unchanged. Not only the LEH closure problem can be alleviated, but also the complicated cross and overlap of laser quads inside the spherical hohlraum in the traditional scheme could be avoided. The novel scheme may provide useful reference for the design of spherical hohlraum structure in laser indirect-driven facilities due to its obvious advantages over the traditional scheme.