# Charged Particles

Charged Particles can be used to define any kinetic particle with given mass and charge.

To add Charged Particles, right click on the “KineticParticles” element, hover over the “Add ParticleSpecies” and choose “Charged Particles”.

kind (not editable)
Charged Particles
nominal density
A positive value suggesting the nominal density for the particles. This will be used in conjunction with the weight setting to compute the density, weights, and number of particles in a macro particle for your kinetic particles.
description
A space to provide a descriptive comment for the particle species.
particle dynamics

Whether to use relativistic or non-relativistic particles.

• relativistic: Use the relativistic particle pushing algorithm to update the particle positions and velocities by including a gamma term.
• non-relativistic: Use the non-relativistic particle pushing algorithm to update the particle positions and velocities.
particle weights

Whether to use constant or variable weight particles.

• variable weights: The weights of the macroparticles can vary throughout the simulation.

• constant weights: The weights of the macroparticles are constant throughout the simulation.

• managed weights: Variable weight particles that are managed to allow for maximum and minimum weights, and maximum and minimum number of macroparticles per cell. Note if working in cylindrical coordinates, some computational artifacts may arise in a few simulation types with managed weights. Contact Tech-X support if this becomes a concern.

macroparticles per cell for splitting

If more than this many macroparticles are in a cell splitting will not occur.

macroparticles per cell for combining

If fewer than this many macroparticles are in a cell combining will not occur.

minimum split particle weight

If the split particles would weigh under this value, splitting will not occur.

maximum combined particle weight

If the combined particle would weigh over this value, combination will not occur.

splitting periodicity

Number of time steps between assessing if particles should be split.

combining periodicity (not editable)

Number of time steps between assessing if particles should be combined.

splitting algorithm

Algorithm to use in determining split particle weights. This interaction is designed to use variable-weight species. Kind of MonteCarlo interaction that splits macroparticles of a single species into two or more macroparticles. This interaction is designed to use variable-weight species. This interaction is applied at each time step. The attribute algorithm_kind specifies the type of algorithm to be used when splitting macroparticles. The possible values are 1 and 2. Algorithm 1 (default) performs a simple, fast split operation, whereas option 2 is more accurate but more computationally intensive. In algorithm 1, the weight of the macro particle is simply split to one half and a new macroparticle gets added at the same location with one half weight value. In algorithm 2, the split operation is done such that the number of macro particles within a cell meets the requirement of the threshold value specified by the user.

combining algorithm

Algorithm to use in determining combined particle weights. Kind of MonteCarlo interaction that combines macroparticles of a single species together into one single macroparticle. The algorithm_kind specifies the kind of algorithm to be used when combining macroparticles. The possible values are 1, 2, 3, 4, 5, or 6. Option 1 indicates a simple pair-wise combination of macroparticles, deleting one and adding the number of real particles (weight) to the other (decimation). Option 2 indicates a slightly more accurate pair-wise approach, deleting one macroparticle and assigning the other the mean position and velocity of the pair as well as the total weight of the pair (inelastic). Option 3 is an elastic combination approach, where quartets of macroparticles are combined into pairs that conserve energy and momentum (elastic). Option 4 is a pair-wise combining approach similar to Option 2 except that it allows users to avoid combining particles that are above the user specified limit. Option 5 is a pairwise approach in which the particles within a cell are grouped in velocity phase-space bins and then particles in each velocity phase-space bin are combined pair-wise. In this approach energy and momentum are conserved. Option 6 is a fluxConserving approach, combining 3+ particles into 2. This has enough degrees of freedom to conserve energy, momentum and a third quantity. We chose the center of momentum frame flux, which has the nice property that the solution is always real. This conserves the original phase space of the particles.

Note

This feature replaces the selfCombCollision previously implemented in Vorpal collision.

weight setting

Whether to use computed weights or explicitly set weights.

• computed weights:

Let VSim calculate your macroparticle weights for you based on the number of macroparticles per cell you specify as well as the nominal density. The weights are calculated such that the number of particles in a macro particle is equal to the nominalDensity * cellVolume / macroparticles per cell.

macroparticles per cell: The number of macroparticles per cell.

• explicitly set weights:

Declare the number of particles in a macro particle explicitly.

particles per macroparticle: The number of particles in a macroparticle.

molecule

Molecule of the charged particle. A custom ion is available for those not pre-defined.

• mass [amu]
The mass of a single real particle in atomic mass units.
• charge number
The charge number of a single particle, multiple of the fundamental charge.
• ionization energy [eV]
The ionization energy of the molecule in electron volts. This value will be used by particle interactions set thresholds and determine energy losses.