Publications

Mode-selective symmetry control for indirect-drive inertial confinement fusion hohlraums

Vesey, Roger A.; Slutz, S.A.; Herrmann, Mark H.; Mehlhorn, Thomas A.; Campbell, R.B.

Achieving a high degree of radiation symmetry is a critical feature of target designs for indirect-drive inertial confinement fusion. Typically, the radiation flux incident on the capsule is required to be uniform to 1% or better. It is generally possible to design a hohlraum that provides low values of higher-order asymmetry (Legendre mode P10 and above) due to geometric averaging effects. Because low-order intrinsic asymmetry (e.g., Legendre modes P2 and P4) are less strongly reduced by geometric averaging alone, the development of innovative control techniques has been an active area of research in the inertial fusion community over the years. Shields placed inside the hohlraum are one example of a technique that has often been proposed and incorporated into hohlraum target designs. Simple mathematical considerations are presented indicating that radiation shields may be designed to specifically tune lower-order modes (e.g., P4) without deleterious effects on the higher order modes. Two-dimensional view factor and radiation-hydrodynamics simulations confirm these results and support such a path to achieving a highly symmetric x-ray flux. The term "mode-selective" is used because these shields, essentially ring structures offset from the capsule, are designed to affect only a specific Legendre mode (or multiple modes) of interest. © 2008 American Institute of Physics.