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Manuscript Title: GLOWCODE: a one-dimensional code for the simulation of plasma afterglows.
Authors: J.W. Long, A.A. Newton, M.C. Sexton
Program title: GLOWCODE
Catalogue identifier: ABUP_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 12(1976)213
Programming language: Fortran.
Computer: ICL SYSTEM 4.
Operating system: MULTIJOB.
RAM: 24K words
Word size: 32
Keywords: Plasma physics, Afterglow, Ionisation, Magnetic confinement, Radiative, Recombination, Diffusion, Implicit, Lagrangian.
Classification: 19.9.

Subprograms used:
Cat Id Title Reference
ABUF_v1_0 OLYMPUS CPC 7(1974)245
ABUF_v2_0 OLYMPUS FOR IBM 370/165 CPC 9(1975)51
ABUF_v3_0 OLYMPUS FOR CDC 6500 CPC 10(1975)167

Nature of problem:
GLOWCODE is a one-dimensional cylindrical code which simulates the decay of a hydrogen plasma in which the dominant loss mechanism is three body collisional-radiative recombination. In addition the processes of ionisation, radiation, diffusion, heat conduction and equipartition are described. Optically thin conditions are assumed; the limiting case of complete opacity can be studied with the appropriate choice of atomic coefficients.

Solution method:
The afterglow is described by the variables ne, ni, na, Te, Ti, Ta which represent the electron density, the ion density, the atom density, electron temperature, ion temperature and atom temperature, respectively. The cylindrical volume is divided into a system of concentric shells and the computation proceeds by solving the various collisional-radiative processes taking place within each shell, and by computing the energy transfer across each shell to its neighbour. At each stage of the calculation pressure balance is re-established by adjusting the cylindrical shells, changing the plasma parameters adiabatically, until the pressure gradient is zero across the plasma radius. Implicit numerical schemes are used for the solution of the conduction and diffusion equations so that there is no stability restriction on the time step for the spatially dependent equations.

The number of cylindrical mesh points can be varied up to a maximum of 41 in the existing program. Ad hoc changes can be made to the code using the EXPERT facility provided by the OLYMPUS package (C.P.C. 7 (1974)245).

Unusual features:
GLOWCODE uses the NAMELIST facility which is not a STANDARD FORTRAN feature. The modular structure and the use of the OLYMPUS package provide the prospective user with a highly adaptable program for the investigation of hydrogen afterglows. Under certain conditions the calculations could possibly fail if highly non-equlibrium pressure situations arise. This is because in the establishment of pressure equilibrium an iterative implicit numerical technique is applied which may not converge if large departures from pressure equilibrium develop. A reduction in the time step should remedy this effect.

Running time:
The execution time depends on the number of mesh points required and on the print out frequency. On the ICL 1905 at Oxford Polytechnic a typical run using 21 mesh points with a print out every 100 steps takes around 1100 s to compute 1000 time-steps. i.e. 0.05 s/mesh point/time- step approximately. The ICL 4/70 at Culham Laboratory takes approximately one-fifth of this time.