Theory of Plasma Simulation Using Finite-Size Particles

The elementary properties of a plasma, in which the small-separation force is smoothed from the Coulomb force, are developed. The modification is considered as being produced by spreading out the charge distribution of a particle to make a particle of finite size R (cloud). These clouds move freely through one another and interact through normal electromagnetic fields. A method to adapt point-particle results for plasma oscillations, shielding, fluctuations, and collisions, is shown, and the modifications to these plasma properties discussed in detail. The relevance of these considerations to computer simulation of plasmas (in which some smoothing is a consequence of the numerical methods used and additional smoothing is sometimes added) is discussed. It is found that smoothing the short wavelength interaction can be used without destroying the desired physics, while suppressing collisional effects and noise at wavelengths < R which are exaggerated in simulation due to the use of far fewer particles than in a real plasma.