Diagnosing radiation drive asymmetry and absorbed energy in ignition Hohlraums using gas-filled capsules

Abstract

The shape of the x-ray self-emission image from an imploded inertial confinement fusion capsule has been used to diagnose Hohlraum radiation drive asymmetry [L. J. Suter et al., Phys. Rev. Lett. 73, 2328 (1994); A. Hauer et al., Rev. Sci. Instrum. 66, 672 (1995); A. Hauer et al., Phys. Plasmas 2, 2488 (1995); N. D. Delameter et al., Phys. Plasmas 3, 2022 (1996)]. Timing of neutron yield from the implosion can also be used to diagnose the absorbed radiation drive energy. We propose a set of beryllium capsules filled with gas, rather than layered cryogenic ice, to diagnose asymmetry and absorbed energy in ignition Hohlraums. Capsules with a range of initial shell thickness have a corresponding range of implosion times, allowing sampling of drive conditions throughout an ignition pulse. For example a 12μm thick shell implodes during the foot of the ignition pulse, sampling the drive up to about 10ns. For such capsules, the foot pulse is a high-adiabat drive and leads to implosions that are rather robust against instability and mixing. In these capsules, the best time to record images for diagnosing asymmetry may be several hundred picoseconds after peak x-ray brightness, when the image distortion is increasing rapidly.