Particle Motion

Direct Simulation Monte Carlo (DSMC) Method

DSMC, or Direct Simulation Monte Carlo, is a particle based method for simulating gas kinetics. Popularized by G.A. Bird in the 60's, this method is now commonly used as an alternative to CFD. In addition, DSMC is commonly combined with PIC codes to include collisions in plasma simulations. This article demonstrates the method with an interactive HTML5 DSMC demo.

Efficient Particle Data Structures

Particle codes have very different memory optimization requirements than fluid-based solvers. Here we consider three types of data structures for holding particles that offer an efficient way of adding and removing particles and compare their performance.

Loading an isotropic velocity distribution

Tutorial on the simple but important topic of loading particles with uniform spatially distributed velocity. This loading is important when loading background gas for particle simulations or when loading drifting Maxwellian beams.

Monte Carlo Collisions (MCC) Example

Monte Carlo Collisions (MCC) is a simple algorithm for modeling particle collisions in situations where the target species is much denser than the source. In this example we use this method to model the charge-exchange (CEX) process in the plume of an ion thruster. We include an animation and the example Java source code.

Charge Exchange Collisions (CEX)

Charge exchange is an important reaction occurring in the plumes of electric propulsion devices. In this reaction, an ion and neutral come into a close contact and exchange an electron without any corresponding change in the momentum of the two particles. In the EP plumes this results in the formation of slow moving ions near the thruster exit. These ions are then accelerated radially out of the plume into areas with no line of sight to the thruster.

Particle Push in Magnetic Field (Boris Method)

A follow up on the previous article, in this tutorial we show you how to integrate the particle motion in the presence of a magnetic field. Inclusion of the magnetic field makes the integration an implicit problem, and care needs to be taken to conserve energy. A simple forward differencing would result in a non-physical energy gain, and the particle would spiral away from the guiding center.

Leapfrog Particle Push (Velocity Integration)

In this article we discuss probably the most fundamental aspect of numerical simulations with the particle in cell (PIC) method: pushing particles. We introduce the commonly used leapfrog method, and provide a simple numerical algorithm in the form of an Excel spreadsheet that implements this method.