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Trace: • logging

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Time dependent logging of averaged surface data

Particle balance at surfaces

During simulation, particles are absorbed and desorbed from surfaces and/or flowing through transparent membranes. In order to better track the current state of the simulation run, these processes are time averaged over physical surfaces and put into ASCII logfiles. The following log files are automatically created during simulation:

  • absorption_log.txt - Particle absorption on surfaces
  • desorption_log.txt - Particle desorption from surfaces
  • transmission_log.txt - Particle flow through transparent membranes
  • pressure_log.txt - Kinetic pressure due to particle impingement on surfaces

By default, 100 log entries are created per simulation run. This number can be modified with the global variable NCOUNTS in the parameter file, e.g. 

NCOUNTS = 1000;

Each of the log files has the physical time in the first column. The other columns contain particle fluxes / pressures according to the headlines given in the file. The choice of columns is performed automatically according to the absorption / desorption mechanisms defined within the wall reactions.

Depending on if the particles are charged/neutral, absorption, desorption and transmission are given in [A] / [sccm]. Both units are proportional to the total number of particles per second:

  • $ 1\,\rm{sccm} = 4.47796\times 10^{17}\,\rm{particles/s} $
  • $ 1\,\rm{A} = 1/q = 6.2415 \times 10^{18}\,\rm{particles/s} = 13.9382\,\rm{sccm}$

For the kinetic pressure $p_{kin}$, the average momentum transfer on surfaces by particle collision is accumulated:

$ p_{kin} = \frac{1}{A \times \delta t}\sum_{i} 2 m_i v_{\perp i} $

The variables are

  • $A$ = Total surface area of physical surface
  • $\delta t$ = Sampling time interval
  • $m_i$ = mass of i'th particle
  • $v_{\perp i}$ = normal velocity of i'th particle

This only works correctly, if the whole area $A$ of the physical surface is in contact with the gas volume. If there is additional area which is not in contact with the gas, the pressure number in the log file is normalized with respect to the whole area and will therefore be lower than the actual pressure in the gas volume.

For transparent membranes pressure logging currently is omitted because the contribution of the net flow through a membrane has to be handled separately, which is not yet working properly.

Potentials of conductive electrodes

The electric potentials for conductive electrodes are being logged into a TXT file potentials_log.txt as a function of time. The time resolution is the same as for the particle-balance related log files such as absorption_log.txt etc. and can be controlled via the NOUNTS parameter. There are the following cases of electrodes:

Dielectric insulating electrodes Since the electric potential on dielectrics is not unique, such surfaces are ignored.
Electrodes with fixed voltage The time-dependent evaluation of the vf parameter is logged.
Single floating electrodes The floating potential is logged.
Double floating electrodes with relative bias The absolute potentials of both electrodes are logged.
RF electrode with self bias Only the self bias is logged.

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