Radiation drive in laser-heated hohlraums

Abstract

Nearly 10 years of Nova [E. M. Campbell, Laser Part. Beams 9, 209 (1991)] experiments and analysis have lead to a relatively detailed quantitative and qualitative understanding of radiation drive in laser-heated hohlraums. Our most successful quantitative modeling tool is two-dimensional (2-D) LASNEX numerical simulations [G. B. Zimmerman and W. L. Kruer, Comments Plasma Phys. Controlled Fusion 2, 51 (1975)]. Analysis of the simulations provides us with insight into the physics of hohlraum drive. In particular we find hohlraum radiation conversion efficiency becomes quite high with longer pulses as the accumulated, high-Z blow-off plasma begins to radiate. Extensive Nova experiments corroborate our quantitative and qualitative understanding.

Observation of High Soft X-Ray Drive in Large-Scale Hohlraums at the National Ignition Facility

“…[10][11][12][13] We find that simulations using less conservative atomic physics and electron heat transport models agree with the measurements and indicate a hohlraum x-ray conversion efficiency of approximately 90%. We find that the total reflected energy due to laser backscatter instabilities is less than 2% of the total incident energy.…”

X-ray spectroscopy from fusion plasmas

“…The comparison of the experimental wall temperatures with simulations [6,40] and scalings [2,50] indicate a laser conversion efficiency into x rays of 80% -90%. This estimate is based on the measured absorbed energy into the hohlraum where SBS and SRS losses are already subtracted.…”

“…This correction, called albedo correction, is performed on calculational basis [40] and corroborated by witness plate measurements [44] and xray emission measurements through the laser entrance hole [6,45,46]. Simultaneously, three independent detection systems have been applied for a complete measurement of the scattering losses.…”

Hard X-ray and hot electron environment in vacuum hohlraums at NIF

“…The x-rays in turn interact with and heat the unilluminated walls producing x-ray ablated plasma and reemitted x-rays. In contrast to laser-disk experiments [2], where the ablated plasma is free to expand, the hohlraum confines and accumulates the plasma [3]. As the plasma moves into the path of the incident laser beam and the hohlraum fills above ≈10% critical density (n c ), hot electrons (> 10 keV) can be produced by laser plasma instabilities such as the stimulated Raman instability.…”