Conceptual design of initial opacity experiments on the national ignition facility
Accurate models of X-ray absorption and re-emission in partly stripped ions are necessary to calculate the structure of stars, the performance of hohlraums for inertial confinement fusion and many other systems in high-energy-density plasma physics. Despite theoretical progress, a persistent discrepancy exists with recent experiments at the Sandia Z facility studying iron in conditions characteristic of the solar radiative–convective transition region. The increased iron opacity measured at Z could help resolve a longstanding issue with the standard solar model, but requires a radical departure for opacity theory. To replicate the Z measurements, an opacity experiment has been designed for the National Facility (NIF). The design uses established techniques scaled to NIF. A laser-heated hohlraum will produce X-ray-heated uniform iron plasmas in local thermodynamic equilibrium (LTE) at temperatures$${\geqslant}150$$ eV and electron densities$${\geqslant}7\times 10^{21}~\text{cm}^{-3}$$. The iron will be probed using continuum X-rays emitted in a$${\sim}200$$ ps,$${\sim}200~\unicode[STIX]{x03BC}\text{m}$$diameter source from a 2 mm diameter polystyrene (CH) capsule implosion. In this design,$2/3$$of the NIF beams deliver 500 kJ to the$${\sim}6$$ mm diameter hohlraum, and the remaining$$1/3$directly drive the CH capsule with 200 kJ. Calculations indicate this capsule backlighter should outshine the iron sample, delivering a point-projection transmission opacity measurement to a time-integrated X-ray spectrometer viewing down the hohlraum axis. Preliminary experiments to develop the backlighter and hohlraum are underway, informing simulated measurements to guide the final design.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC52-07NA27344
- OSTI ID:
- 1358319
- Report Number(s):
- LLNL-JRNL-700383; applab
- Journal Information:
- Journal of Plasma Physics, Vol. 83, Issue 01; ISSN 0022-3778
- Publisher:
- Cambridge University Press
- Country of Publication:
- United States
- Language:
- English
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