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Manuscript Title: BOLTZ: a code to solve the transport equation for electron distributions and then calculate transport coefficients and vibrational excitation rates in gases with applied fields.
Authors: R.M. Thomson, K. Smith, A.R. Davies
Program title: BOLTZ
Catalogue identifier: ACWX_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 11(1976)369
Programming language: Fortran.
Computer: ICL 1906A.
Operating system: GEORGE 4.
RAM: 200K words
Word size: 48
Keywords: Boltzmann equation, Electron distribution, Transport coefficients, Vibrational Excitation rates, Laser physics, Plasma physics.
Classification: 15, 19.11.

Nature of problem:
BOLTZ is a set of two programs which calculates the electron distribution, transport coefficients, and electron vibrational excitation rates in a gas mixture with an applied electric field. With the test deck provided, BOLTZ calculates the excitation rates needed for TLASER - a laser kinetics code for CO2 : N2 : He lasers. Given the necessary cross-section data BOLTZ will calculate the electron distribution etc. for any gas mixture.

Solution method:
The program solves the time-independent Botlzmann equation for the electron energy distribution function in a gas mixture. Following Rockwood the Boltzmann equation is written in terms of the electron energy density. By partitioning the electron energy axis into K cells the time independent Boltzmann equation is converted to a set of K simultaneous linear equations. The equivalent matrix equation is first solved ignoring the effects of superelastic collisions, in which case the matrix is upper Hessenberg. The solution of the matrix equation proceeds rapidly by back-substitution. The vibrational excitation rates and transport coefficients are then obtained as the appropriate weighted integrals over the electron number density distribution. The program then solves the matrix equation taking into account the effect of superelastic collisions. The matrix is then a full matrix and the solution for the electron distribution is first obtained for a coarse mesh by converting the matrix to upper triangular form by column pivoting and solving by back substitution. The solution is interpolated to a fine mesh and is used as the initial guess to solve the matrix equation by Gauss-Seidel iteration.

Up to nine gases may be included. The value of the applied field has an upper limit set by the amount of store available for the matrix elements.