Novel free-form hohlraum shape design and optimization for laser-driven inertial confinement fusion

Abstract

The hohlraum shape attracts considerable attention because there is no successful ignition method for laser-driven inertial confinement fusion at the National Ignition Facility. The available hohlraums are typically designed with simple conic curves, including ellipses, parabolas, arcs, or Lame curves, which allow only a few design parameters for the shape optimization, making it difficult to improve the performance, e.g., the energy coupling efficiency or radiation drive symmetry. A novel free-form hohlraum design and optimization approach based on the non-uniform rational basis spline (NURBS) model is proposed. In the present study, (1) all kinds of hohlraum shapes can be uniformly represented using NURBS, which is greatly beneficial for obtaining the optimal available hohlraum shapes, and (2) such free-form uniform representation enables us to obtain an optimal shape over a large design domain for the hohlraum with a more uniform radiation and higher drive temperature of the fuel capsule. Finally, a hohlraum is optimized and evaluated with respect to the drive temperature and symmetry at the Shenguang III laser facility in China. The drive temperature and symmetry results indicate that such a free-form representation is advantageous over available hohlraum shapes because it can substantially expand the shape design domain so as to obtain an optimal hohlraum with high performance.

Preliminary study on a tetrahedral hohlraum with four half-cylindrical cavities for indirectly driven inertial confinement fusion

“…The greatest challenges on the approach to ignition utilizing the cylindrical hohlraum configuration might reside in the drive symmetry and the LPIs, such as the significant stimulated Raman scatter (SRS) of the inner-cone beams [14] and cross-beam energy transfer (CBET) between the innercone and outer-cone beams [15], which would detract from the time-dependent drive symmetry [11]. These key challenges might still reside in the rugby-like hohlraums [16][17][18][19][20] with two LEHs. To date, diverse spherical hohlraums, upon which two [21,22], three [23], four [21,[24][25][26][27][28][29][30], six [31][32][33][34], or twelve [21] holes are drilled, with several sets of laser beams with different incident angles, have been investigated on the laser facilities of Iskra-5, OMEGA, or NIF.…”

“…the laser spots and the wall, which are assumed as separate homogeneous background by neglecting the flux difference within each section. In par ticular, IRAD3D can rapidly provide insight into the drive symmetry on the capsule under a variety of circumstances [44] and has been used for hohlraum shape optimization [16,45] and experimental data interpretation [46] in ICF.…”

“…A slight change in the shape of a hohlraum can improve the hohlraum performance [16]. There are three factors impacting the hohlraum performance: the drive symmetry, coupling efficiency, and plasma filling affecting the LPIs, which depend on the hohlraum configuration.…”

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

“…The indirect drive (ID) scheme has been proposed in which the laser beam energy is absorbed and converted into x-rays inside a high-Z cavity (hohlraum) to provide a highly uniform x-ray radiation field. 11,12 Recently, a series of hohlraums [13][14][15][16][17] with rugby and spherical shapes have been considered to improve implosion performance. The ID scheme promises high irradiation uniformity at the price of lower energy efficiency.…”

Comparison of three hohlraum configurations with six laser entrance holes for indirect-drive inertial confinement fusion

“…the considerable simulated Raman scatter (SRS) of the inner-quad beams [13] and cross-beam energy transfer (CBET) [14] near the LEHs, which would worsen the time-dependent drive symmetry [9,10] and degrade the implosion performance [15]. These daunting issues might still reside in the rugby-shaped geometries [16][17][18][19][20][21][22][23][24] with the same two LEHs and multi-cone quads.…”