High-temperature hohlraum designs with multiple laser-entrance holes

Abstract

Multiple laser-entrance-hole (LEH) designs are proposed which increase the number of LEHs, n, from two in standard designs. This is done to minimize the laser travel distance in the hohlraum and to obtain algebraically vanishing low order radiation moments, thereby allowing smaller case-to-capsule ratios. This leads to higher coupling efficiencies and temperatures. Symmetry is analyzed using group theory for n ≤ 12 with the LEHs placed at points given by solutions to the Thomson problem. Symmetry is improved beyond the standard n = 2 designs for n corresponding to Platonic solids: the tetrahedron (n = 4), octahedron (n = 6), and icosahedron (n = 12). The first, non-vanishing asymmetry present in the radiation drive is given. Two-dimensional radiation-hydrodynamic simulations are then performed using Lasnex to assess energetics for n = 4 and n = 12. The simulation domain is a conical section of a sphere with the total solid angle equal to 4π/n. The total LEH area is kept fixed as n increases, reducing the size of an individual LEH and the laser spot size. A foam block is recessed inside the LEH in order to capture all of the incident laser energy and prevent the rays from propagating large distances across the hohlraum. The radiation temperature near the capsule reaches ∼335 eV with a 400 TW peak laser power, and the electron density inside the LEH remains below quarter-critical density.

Characterization of radiation drive by measuring the localized re-emitted flux from the capsule in inertial confinement fusion experiments

“…Thirdly, the influence from the LEH closure can be avoided. Lastly, this method presents a new way for the evaluation of the drive flux in novel hohlraums, such as three-axis cylindrical hohlraums [42] and other alternatives hohlraums [43], for which the radiation fluxes escaping from different LEHs cannot be distinguished experimentally using Dante spectrometer or FXRD detector, and novel methods are urgently needed for the evaluation of the drive flux.…”