Temporal and spatial filtering remedies for dispersion in electromagnetic particle codes
There has been considerable interest over the last decade in the physics of intense electromagnetic signals in plasmas -- much of it in the context of laser fusion and pulsar astrophysics. Simulations of these phenomena test the limits of particle simulation and in particular the standard leapfrog algorithm for advancing the electromagnetic fields. As shock fronts and sheaths develop within the plasma in response to intense electromagnetic waves, numerical dispersion in trinsic to the leapfrog algorithm can cause unphysical ripples to appear in the field solution which can interact with particles. Fourier analysis of the leapfrog scheme in 1D yields the dispersion relation for a Courant number /nu/ /triple bond/ c/Delta/t//Delta/x = 0.5. As we can see, the phase velocity of the modes falls off the light line at high k/Delta/x. Thus modes that are poorly resolved will tend to disperse and trail the main pulse as ripples. There are several approaches to finding a remedy for these ripples. High-order finite difference methods can be considerably less dispersive. Also, improving resolution can move the physics to lower k/Delta/x where the dispersion is less. Often these options are not available, either because of difficulty in implementation or because computer resources are insufficient. This leaves filtering as the main option, with two routes to schemes that remove high k/Delta/x modes -- temporal and spatial filtering. In this paper we present techniques to remove dispersion from particle simulations using both methods. 5 refs., 1 fig.
- Research Organization:
- Lawrence Livermore National Lab., CA (USA)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5808584
- Report Number(s):
- UCRL-101395; CONF-890931-7; ON: DE89017534
- Country of Publication:
- United States
- Language:
- English
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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
700101* -- Fusion Energy-- Plasma Research-- Confinement
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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALGORITHMS
COMPUTERIZED SIMULATION
COSMIC RADIO SOURCES
DISPERSION RELATIONS
ELECTROMAGNETIC FIELDS
FINITE DIFFERENCE METHOD
ITERATIVE METHODS
LASER-PRODUCED PLASMA
MATHEMATICAL LOGIC
NUMERICAL SOLUTION
PLASMA
PULSARS
SIMULATION