LIFE Chamber Chemical Equilibrium Simulations with Additive Hydrogen, Oxygen, and Nitrogen Page: 3 of 32
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LIFE Chamber Chemical Equilibrium Simulations with Additive Hydrogen, Oxygen, and Nitrogen
James A. DeMuth and Aaron J. Simon
Lawrence Livermore National Laboratory
In order to enable continuous operation of a Laser Inertial confinement Fusion Energy (LIFE)
engine, the material (fill-gas and debris) in the fusion chamber must be carefully managed. The
chamber chemical equilibrium compositions for post-shot mixtures are evaluated to determine
what compounds will be formed at temperatures 300-5000K. It is desired to know if carbon and
or lead will deposit on the walls of the chamber, and if so: at what temperature, and what
elements can be added to prevent this from happening. The simulation was conducted using
the chemical equilibrium solver Cantera with a Matlab front-end . Solutions were obtained by
running equilibrations at constant temperature and constant specific volume over the specified
range of temperatures. It was found that if nothing is done, carbon will deposit on the walls
once it cools to below 2138K, and lead below 838K. Three solutions to capture the carbon were
found: adding pure oxygen, hydrogen/nitrogen combo, and adding pure nitrogen. The best of
these was the addition of oxygen which would readily form CO at around 4000K. To determine
the temperature at which carbon would deposit on the walls, temperature solutions to
evaporation rate equations needed to be found. To determine how much carbon or any species
was in the chamber at a given time, chamber flushing equations needed to be developed.
Major concerns are deposition of carbon and/or oxygen on the tungsten walls forming tungsten
oxides or tungsten carbide which could cause embrittlement and cause failure of the first wall.
Further research is needed.
This work performed under the auspices of the U.S. Department of Energy by Lawrence
Livermore National Laboratory under Contract DE-AC52-07NA27344.
The LIFE Chamber Chemical Equilibrium Study was performed to better understand the
different compounds that would form when a target of specified composition was ignited inside
the chamber at various temperatures ranging from 300 to 5000K. A chemical equilibrium solver,
Cantera, was used to solve for the compound distributions inside the chamber. In equilibration
Cantera minimizes the free energy of the system by distributing individual atoms among a pre-
defined list of compounds at a specified temperature and specific volume. Specific heat data
fits are taken from the NASA Thermo Tables and are used by Cantera to calculate Gibbs free
energy for all the possible compounds.
In the LIFE chamber, there will be an initial density of Xenon at 4- , into which a
hohlraum will be injected and ignited. The temperatures will reach levels of 5000K or higher
initially, but will immediately cool. As the components of the hohlraum cool they will begin to
form compounds or condense/solidify onto the surrounding cooler walls of the system. The
main concern is that for a hohlraum made of Pb, C, Ta, N, O, H, D, and T, the Lead and the
Carbon would condense or deposit respectively on the walls of the chamber. Tantalum could
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DeMuth, J A & Simon, A J. LIFE Chamber Chemical Equilibrium Simulations with Additive Hydrogen, Oxygen, and Nitrogen, report, September 3, 2009; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc1014961/m1/3/: accessed August 14, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.