Tracking Solver Overview

The tracking solver is primarily capable of tracking charged particles through electro- and magnetostatic fields. The governing equation of the particle tracking are the momentum and position update:

	Analytic	Discrete
Momentum update:
Position update:

The CST PARTICLE STUDIO® offers multiple emission models for particles leaving a cathode.

Particle Tracking

The particle tracking simply computes the trajectory of the particles through a pre-calculated electromagnetic field. Since electric and magnetic fields are computed on

a computation grid, it is necessary to interpolate the fields to the particle position with a linear interpolation scheme.

Optionally the particles' current and space charge can be computed. This simple tracking procedure does not consider any reaction of the particles' movement back to the electromagnetic field.

Gun-Iteration

The gun-iteration consists of an iterative application of electrostatic solver and particle tracker. After calculating the electrostatic field the particles are emitted and tracked and there space charge is monitored. This space charge is used to modify the right hand side of the electrostatic solver (the charge-vector). Afterwards a new electrostatic field is calculated which incorporates some knowledge of the particles' flight path. This procedure is repeated until the relative difference of the emitted current and space charge meets a specific convergence criteria. The flow chart of the gun solver results in:

The convergence curve in dB can be checked in the 1D Result folder (Gun Code Accuracy). It is calculated from the relative difference of the charge-distribution q between two subsequent calculation steps (steps i and i+1).

For visualization purposes the logarithmic values are recorded:

Note: During each tracking calculation only one set of particles is emitted but the resulting trajectory and electromagnetic field reflect the behaviour of a continuous particle beam. This kind of self-consistent gun simulation is only capable of simulating a steady-state particle beam and can not be used for simulating transient effects as the switching characteristic of an emitting source.