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Manuscript Title: RAMSES: a two-dimensional, PIC type laser pulse propagation code.
Authors: H.D. Dudder, D.B. Henderson
Program title: RAMSES
Catalogue identifier: ABUL_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 10(1975)155
Programming language: Fortran.
Computer: ICL 4/70.
Operating system: ICL MULTIJOB.
RAM: 199K words
Word size: 8
Keywords: Plasma physics, Laser physics, Particle code, Inertial confinement, two-dimensional, Simulation, Trajectories, Refraction, Pulse, Laser target, Focusing, Defocusing, Olympus, Laser fusion, Fusion reactor, Laser propagation.
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

Nature of problem:
The model used in RAMSES is intended to study the propagation of a laser pulse through a background gas or plasma. The laser pulse is composed of macroscopic photons whose trajectories are calculated. Gradients in the refractive index, which may be computed self- consistently from photoionization of the plasma, change the direction of the photons and this can lead to focusing or defocusing of the pulse. Rotational symmetry is assumed for both the laser pulse and the background. Computations with the model may support laser-fusion reactor studies and laser-target studies as well as general work on the propagation of laser light.

Solution method:
A particle simulation model has been applied to the problem of calculat- ing the trajectories of macroscopic photons. The photons carry variable amounts of energy in order to obtain arbitrary pulse shapes. The model evaluates the refractive index from the local electron density which may be supplied either explicitly or calculated self-consistently from local densities and ionization rates. The gradients of the refractive index determine the photon motion using a two-step predictor- corrector scheme. Analytic functions for ionization rates, pulse shape and neutral and electron density profiles are tabled in appropriate FUNCTION subprograms which may be amended as necessary.

Only initially parallel or focused laser pulse can be computed. The background density is assumed to be time-dependent if ionization is involved, but if the electron density is supplied explicitly it may also be time-dependent.

Unusual features:
RAMSES is written in Standard Fortran except for the use of the NAMELIST facility. The structure of the program is based on the OLYMPUS system which facilitates a transfer to other computers. The graphical output package is excluded since it makes use of the Culham GHOST system which is not generally available. SI units are used throughout the code.