Neutral Particles

Neutral Particles of the gas kinds listed below are pre-defined with the appropriate charge and mass values. Users can also add custom neutral species.

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

kind (not editable)

Neutral 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. This is converted into a STFunc which is set to a constant in Cartesian coordinates. In cylindrical coordinates, it is important to recognize that the volume of a cell is a function of radius. Therefore, when a gas is in equilibrium, then statistically one expects to find fewer particles in a cell for small values of R. As a result, to maintain an equilibrium density in cylindrical coordinates, this thresholdFunc would be smaller for small values of R and larger for large values of R. The following function is used to determine the number of particles per cell for splitting: \(max(1.0,THRESHOLD*10^(1.5*(y/MAXR) - 0.75))\), where THRESHOLD is the value you specify in Composer, and MAXR is the maximum R grid value. If you want flexibility in adjusting this function,please contact Tech-X customer support.

    macroparticles per cell for combining

    If fewer than this many macroparticles are in a cell combining will not occur. All other aspects to this capability are otherwise similar to the “macroparticles per cell for splitting” described above.

    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.

    combining algorithm

    Algorithm to use in determining combined particle weights.

    maintain equilibrium (cylindrical only)

    If set to True, in cylindrical coordinates the combining and splitting thresholds will be modified to the following equation. max(1.0, threshold*10**(1.5*y/LY-0.75)) This attempts to handle the fact that cylindrical cells will increase in size as the value of r increases.

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 neutral particle. Options are:

  • H: Hydrogen (atomic)

  • H2: Hydrogen (molecular)

  • He: Helium

  • Ar: Argon

  • Xe: Xenon

  • Rn: Radon

  • Kr: Krypton

  • O: Oxygen (atomic)

  • O2: Oxygen (molecular)

  • Ne: Neon

  • N: Nitrogen (atomic)

  • N2: Nitrogen (molecular)

  • custom molecule

    Set the mass (in amu) and ionization energy (in eV) of a custom gas.

    • mass [amu] The mass of a single real particle in atomic mass units.

    • ionization energy [eV] The ionization energy of the molecule in electron volts.

Additional Features:

Emitters:

Boundary Conditions:

Loaders: