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Manuscript Title: MEDUSA - a one-dimensional laser fusion code.
Authors: J.P. Christiansen, D.E.T.F. Ashby, K.V. Roberts
Program title: MEDUSA
Catalogue identifier: ABUG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 7(1974)271
Programming language: Fortran.
Computer: ICL 4-70.
Operating system: ICL MULTIJOB.
RAM: 45K words
Word size: 32
Keywords: Plasma physics, Laser physics, Fusion, Inertial confinement, One dimensional, Lagrangian, Two-temperature, Implicit.
Classification: 15, 19.7.

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

Revision history:
Type Tit le Reference
correction 000A CORRECTION 15/8/75 See below

Nature of problem:
The feasibility of laser fusion as a method for generating controlled thermonuclear power has so far been mainly based on computer simulation. MEDUSA 1 has been written to investigate in one space dimension some of the hydrodynamic and plasma processes that take place in a small pellet which is irradiated by laser light.

Solution method:
The plasma is described by 4 main dependent variables rho, u, Ti, Te, which represent respectively the density, velocity and ion and electron temperatures. These are functions of the time t and of a single space variable r which can be chosen to correspond to slab, cylindrical or spherical geometry as required. Subsidiary variables represent the chemical composition of the plasma in terms of the fractions of the various ionic species that are present, the composition varying in space and time due to the thermonuclear reactions that occur. The Navier-Stokes equations are supplemented by separate heat conduction equations for the ion and electron temperatures and a variety of additional effects are included. A lagrangian difference mesh is employed, the integration scheme being explicit for the hydrodynamics, and implicit for the heat conduction equations using the Crank-Nicholson scheme and the Gauss elimination method. Several iterations are performed at each timestep in order to take into account the non-linear dependence of the physical coefficients on the density and temperatures and to ensure convergence.

Restrictions:
Version 1 of MEDUSA is intended to provide as simple a model of the laser fusion process as possible, and a number of physical phenomena and situations have therefore been omitted which may be included in later versions. Ad hoc sections of code can however be inserted at many points throughout the program in order to modify the working of the standard version for specific runs using the EXPERT facility. MEDUSA 1 will accept any realistically programmed laser pulse and will describe the resulting plasma phenomena with an accuracy that depends on the mesh size as well as on the convergence criteria. The maximum permissible mesh size is determined by the size of core store of the computer employed.

Unusual features:
MEDUSA 1 is written in Standard Fortran except for the use of the NAMELIST facility, and is optimized for speed rather than memory requirements. Subsets of the physics can be employed if appropriate logical switches are set. The structure of the whole program is highly modular and uses the OLYMPUS control and utility package described in Comp. Phys. Coummun. 7(1974)245and 237. The graphical output section which is part of the program at the Culham Laboratory has been excluded from the published version since it uses the GHOST Graphical Output System which is not generally available.

Running time:
Execution times depend on the mesh size and convergence criteria. On the ICL 4/70 at Culham Laboratory, 1000 timesteps with a maximum of 5 iterations per timestep take 300 s for a mesh size of 40.

CORRECTION SUMMARY
Manuscript Title: MEDUSA - a one-dimensional laser fusion code. (C.P.C. 7(1974)271).
Authors: J.P. Christiansen, D.E.T.F. Ashby, K.V. Roberts
Program title: 000A CORRECTION 15/8/75
Catalogue identifier: ABUG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 10(1975)251
Classification: 15, 19.7.