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Manuscript Title: FIRE: a code for computing the response of an inertial confinement fusion cavity gas to a target explosion.
Authors: T.J. McCarville, R.R. Peterson, G.A. Moses
Program title: FIRE
Catalogue identifier: AAHP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 28(1983)367
Programming language: Fortran.
Computer: UNIVAC 1110.
Operating system: UNIVAC 1110 EXEC VIII.
RAM: 60K words
Word size: 36
Peripherals: disc.
Keywords: Inertial confinement Fusion reactor design, Deposition of target X-ray, Deposition of target Debris, Gas protection concept, Plasma physics, Laser physics, Cavity gas response.
Classification: 15, 19.7.

Subprograms used:
Cat Id Title Reference
AAHO_v1_0 MIXERG CPC 28(1983)405

Nature of problem:
One of the methods that has been suggested for protecting the first wall of a commercial inertial confinement fusion (ICF) reactor from the X-rays and ions emitted by an exploding target is to fill the cavity with a gas. The Fire code described in this article simulates the interaction of the target X-rays and ions with the gas, and computes the response of the gas to a target explosion. The results computed by the Fire code are useful for analyzing the thermal and mechanical response of a first wall that is protected with a cavity gas.

Solution method:
The deposition of target X-rays into the gas is computed with an expotential attenuation model. A table of X-ray attenuation coefficients for atoms with atomic numbers ranging from 1 to 100 and X- ray energies ranging from 0.01 keV to 1 MeV is supplied with this version of the code. The initial X-rays that are absorbed ionize the gas near the target, and reduce the photoelectric attenuation coefficient for subsequent X-rays. The X-ray deposition model used by by the FIRE code accounts for the reduction in the attenuation coefficient with increasing ionization. The internal energy and momentum transferred from the target debris to the gas are computed from the results of an ion transport code. The results of the ion transport code are fit to analytic functions, and these analytic functions are used to estimate the rates at which internal energy and momentum are deposited as functions of time and space. The FIRE code simulates the response of a cavity gas to the deposition of target X-rays and ions by solving differential equations of energy and momentum conservation. These equations are solved in the Lagrangian reference frame by finite difference methods. A tabulated equation of state and tabulated Planck and Rosseland mean free paths are needed to compute the response of the gas. The MIXER code has been developed to compute this data for the FIRE code. The TSTRESS code then uses the heat fluxes and overpressures at the first wall computed by FIRE to analyze the response of the first wall.

The FIRE code assumes one-dimensional symmetry in computing the interaction of the target X-rays and ions with the gas, and also in computing the gas response. The cavity gas can be divided into a maximum of 97 Lagrangian zones, and either planar, cylindrical or spherical geometry can be assumed. The gas is assumed to be composed of only one atomic number in computing the X-ray deposition. At present, the model for computing the reduction in the photoelectric attenuation coefficient with increasing ionization is only used if the gas is neon, argon or xenon. To compute the reduction in the attenuation coefficient for additional gases, the energy of the K, L and M shells of the neutral gas and the number of electrons in each shell must be added to the subroutine EDATA.

Unusual features:
The FIRE code is written in standard FORTRAN except for the manner in which the COMMON blocks are used. The COMMON blocks are listed only at the beginning of the program, where they are equated to INCLUDE statements. Thereafter, the INCLUDE statements are used to represent the COMMON blocks. The use of INCLUDE statemenets abberviates the listing of a program that uses the same COMMON blocks in many subroutines, beacuse an INCLUDE statement occupies only one line, whereas a COMMON block might occupy many lines. InCLUDE statements only have meaning to a Univac compiler, so the user may wish to replace them with the respective COMMON blocks.

Running time:
The CPU time required to compute the deposition of target X-rays and ions into the gas is minimal compared to the time required to compute the gas response. On the Univac 1110, the CPU running time required to compute the gas response is about 2*10**-3s /zone cycle.