Length scaling of dynamic-hohlraum axial radiation

Abstract

Radiation generated within a 10-mm-long foam-target DH (dynamic hohlraum) is used for high-temperature (>200 eV) radiation-flow and inertial-confinement-fusion studies [Sanford et al., Phys. Plasmas 9, 3573 (2002)]. The length of this DH is varied from 5 to 20 mm, keeping the mass/unit length constant in an effort to study the scaling of axial radiation power with length, and better understand its production. Measurements show a greater variation in this power with length than would be expected from simple arguments [Slutz et al., Phys. Plasmas 8, 1673 (2001)]. Maximum axial power of ∼10 TW is produced with a length of ∼7.5 mm, similar to the typical power for the baseline 10 mm DH. The decreasing axial power (at a rate of ∼0.65 TW per mm at longer lengths) is bounded by radiation-magnetohydrodynamic simulations [Peterson et al., Phys. Plasmas 6, 2178 (1999)] that include the development of the magnetic Rayleigh–Taylor instability in the r–z plane. The dramatic drop in axial power below 7.5 mm, by contrast, was unanticipated. This decrease suggests the presence of differing mechanisms for limiting power at short and long lengths.