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

Runge, J.; Logan, B. G.
March 2009
Physics of Plasmas;Mar2009, Vol. 16 Issue 3, p033109
Academic Journal
A key issue in heavy-ion beam inertial confinement fusion is target interaction, especially implosion symmetry. In this paper the two-dimensional beam irradiation nonuniformity on the surface of a spherical target is studied. This is a first step to studies of three-dimensional dynamical effects on target implosion. So far nonrotated 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 modeled 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.


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