Dynamic hohlraum driven inertial fusion capsules

A dynamic hohlraum is formed when an imploding annular cylindrical Z-pinch driven plasma collides with an internal low density convertor. This collision generates an inward traveling shock wave that emits x rays, which are trapped by the optically thick Z-pinch plasma and can be used to drive an inertial fusion capsule embedded in the convertor. This scheme has the potential to efficiently drive high yield capsules due to the close coupling between the intense radiation generation and the capsule. In prior dynamic hohlraum experiments [J. E. Bailey et al., Phys. Rev Lett. 89, 095004 (2002)] the convertor shock wave has been imaged with gated x-ray pinhole cameras. The shock emission was observed to be very circular and to be quite narrow in the radial direction. This implies that there is minimal Rayleigh-Taylor imprinting on the shock wave. Thus, the dominant source of radiation asymmetry is not random and in principle could be significantly decreased by proper design. Due to the closed geometry of the dynamic hohlraum, the most convenient way to diagnose the radiation symmetry is to image the x rays from the core of an imploded capsule. However, the core temperatures in the prior experiments were not high enough to obtain images. Using numerical simulations we have redesigned the dynamic hohlraum to obtain higher capsule core temperatures. This has enabled us to obtain x-ray pinhole images and Ar K-shell spectra from the imploded cores of 1.7-2.0 mm diameter CH-wall capsules filled with either D2 or CD4 and doped with a small amount of Ar. These capsules absorbed approximately 20 kJ of x-ray energy from the radiation drive, which peaked at a temperature of about 200 eV. Core temperatures of approximately 1 keV were inferred from the Ar spectrum. Our present understanding of the physics of dynamic hohlraums is presented along with our plans to improve this system