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Information stored in picmc cell structure

Most of the data volume is given as time- and particle averaged values within the cell structure. They are provided as POS files which can be viewed and further processed within GMSH.

These data can comprise information on gaseous species as well as on particle absorption and status of walls. Additionally, some data on particle absorption can be also given in the resolution of the surface mesh.

The time-averaging feature is activated by setting TAVG=1; at top of the parameter file. By setting TAVG=0; momentary snapshots are displayed instead, however in most cases they will be quite noisy or a very large number of particles has to be simulated to get reasonable statistics. Therefore, TAVG=1; is the default setting.

The number of time averages within the whole physical simulation time interval is defined in the variable NPLOTS at top of the parameter file. The selection of output data by species is defined via lists in the upper part of the parameter file.

The following lists for cell-oriented information are available:

  • Information on gaseous species
    • NUMBER = Number of simulation particles per cell
    • DENSITY = Density of simulation particles in physical units [1/m³]
    • PRESSURE = Partial pressure in [Pa]
    • TEMPERATURE = Translational kinetic temperature in [K]
    • ENERGY = Mean particle energy in [eV]
    • VELOCITY = Mean particle velocity in [m/s]. This is a vector plot for three components vx, vy, vz.
  • Information on wall absorption and wall state
    • ABSORPTION = Particle absorption on walls in [1/m²s]
    • DESORPTION = Particle desorption from walls in [1/m²s]
    • COVERAGE = Surface coverage fraction of a wall material (between 0 and 1)
    • DEPOSITION = Deposition rate of a wall material [nm/s]
  • Information on fields
    • FIELD = Quantities concerning electromagnetic field computation

All of these data go into sub folders of the simulation data folder. This behaviour can be suppressed by setting SINGLE_PLOT_FOLDER=1; (which can be found in the bottom part of the parameter file).

The filename structure is <type>_<species>_<time>ms.pos, e.g. the Ti absorption after 50 ms will be stored in a file absorption/absorption_Ti_50.00ms.pos. These files can be opened and further processes in GMSH.

The list COLLISION enables the plotting of collision statistics on quad resolution for every used cross section defined in the sigma.r file. By putting a species name in that list all reactions involving this species are written in a separate file including the energy threshold to identify the corresponding cross section. The weighted sum of all quads for a specific collision matches the total collision rate written in the collision.txt files present in the same folder.

Additionally, with the list MESHDATA particle absorption information is given in the resolution of the surface mesh. The filename for mesh absorption data for Ti after 50 ms will be e.g. meshdata/meshdata_Ti_50.00ms.pos. These data files contain multiple plots:

  • Absorption
  • Desorption
  • Mean energy of absorbed particles
  • Mean angle of incidence α
  • Mean cos(α)

The POSITION list has to be handled with care. If you put a species in there, for all particles of that species the position and energy is plotted. This plot is used normally with a low number of particles, e.g. a high NREAL or individually distributed particles with the Init_Particles block. An example would be the movement of single electrons in the electromagnetic field.

A typical setting of these lists may look as follows:

# ===================================================== #
# 3D data extraction                                    #
# Examples: NUMBER = ["Ar", "e"]; FIELD = ["PHI", "E"]; #
# ===================================================== #
NUMBER      = [];
DENSITY     = [];
PRESSURE    = ["Ar", "O2", "Ti"];
ENERGY      = [];
VELOCITY    = ["Ar", "O2", "Ti"];
ABSORPTION  = ["Ti"]; 
DESORPTION  = ["Ti"]; 
MESHDATA    = ["Ti"];
# POSITION plots can get very large, so handle with care!
POSITION    = [];
# "PHI" = electric potential, "PHI_MEAN" = time averaged electric potential, "E" = electric field
# "JICP" = source current density, "EICP" = current induced electric field, "BICP" = current induced magnetic field
FIELD       = [];
# For COVERAGE and DEPOSITION fill in required surface materials:
COVERAGE    = ["TiO2"];
DEPOSITION  = ["Ti_metal", "TiO2"];

With these settings, the pressure and velocity are plotted for three species, Ar, O2 and Ti, respectively. For Ti, additionally the absorption plot in cell resolution and absorption data in mesh resolution are generated. Finally, for wall materials TiO2 and Ti_metal the deposition rate is plotted together with the surface coverage fraction for TiO2.