Nonuniformity for rotated beam illumination in directly driven heavy-ion fusion

Abstract

A bstractA key issue in heavy-ion beam inertial confinement fusion is target interaction, especially implosion symmetry. In this paper the 2D beam irradiation nonuniformity on the surface of a spherical target is studied. This is a first step to studies of 3D dynamical effects on target implosion. So far non-rotated beams have been studied. Because normal incidence may increase Rayleigh-Taylor instabilities, it has been suggested to rotate beams (to increase average uniformity) and hit the target tangentially. The level of beam irradiation uniformity, beam spill and normal incidence is calculated in this paper. In Mathematica the rotated beams are modelled as an annular integrated Gaussian beam. To simplify the chamber geometry, the illumination scheme is not a 4π system, but the beams are arranged on few polar rings around the target. The position of the beam spot rings is efficiently optimized using the analytical model. The number of rings and beams, rotation radii and widths are studied to optimize uniformity and spilled intensity. The results demonstrate that for a 60-beam system on four rings Peak-To-Valley nonuniformities of under 0.5% are possible. * Electronic address:

Spiral wobbling beam illumination uniformity in HIF fuel target implosion

“…In the time averaged energy deposition onto a spherical direct drive target, the averaged illumination nonuniformity was small, for example, less than a few percent [6]. However, it was found that the initial imprint of the rotating axis HIBs is serious and introduces a large illumination nonuniformity.…”

“…So far the wobbling HIBs illumination has been considered by the time averaged illumination [3][4][5][6]. In the time averaged energy deposition onto a spherical direct drive target, the averaged illumination nonuniformity was small, for example, less than a few percent [6].…”

“…By the spiraling trajectory of the HIB axis, a sufficiently small nonuniformity is successfully realized, and a small part of the HIBs particles do not hit the target in order to obtain the illumination high uniformity. The spectral analyses for the HIBs illumination nonuniformity are also performed based on the spherical harmonic function [5,6] and show that the mode (n, m) = (2, 0) is dominant throughout the HIBs illumination. Figure 5 shows the amplitude of the mode (2, 0) versus time, and Fig.…”

“…1), Ref. [5] shows a sufficiently small nonuniformity for circulaly wobbling HIBs in their steady state, and the nonuniformity is evaluated after the wobbling HIBs energy deposition is steady [6]. However, the wobbling HIBs illumination is time-dependent.…”

“…The 3-D HIBs illumination detail studies show that HIBs illumination uniformity depends strongly on the HIBs illumination scheme [5,6]. For the wobbling HIBs illumination (see Fig.…”