Writing output

Supported output types

By default, output is written in the Silo format. More information about this format and other output options can be found in the Afivo documentation.

Description of variables

name	meaning
e	Electron density (1/m3)
electric_fld	Electric field strength (V/m)
M_min	Negative ion species (if no chemistry is defined) (1/m3)
M_plus	Positive ion species (if no chemistry is defined) (1/m3)
phi	Electric potential (V)
rhs	-rho/eps0, right-hand side for Poisson's equation, where rho is the charge density and eps0 the dielectric permittivity of vacuum.

Species defined by the plasma chemistry will also be present in the output.

Binary output

Afivo-streamer allows a simulation to be continued at a later time through the use of binary output files (DAT files). To do this, the simulation is initially run and set up to write DAT files, which could be achieved by using the following .cfg file options:

• datfile%write - set to true if you want to write DAT files
• datfile%per_outputs - control when DAT files are written by equating this to an integer (e.g. datfile%per_outputs = 20 means that a DAT file is created every after 20 output files are written)

The created DAT files would have the same name as the SILO files written by the program. To begin another simulation run from a particular DAT file, set the flag restart_from_file equal to a string with the name (and location, if in a different directory) of the DAT file you want to use as the starting point of the other simulation run.

The log file

The log file is a text file containing information about the physics and numerical properties of the simulation. It is possible to write extra variables to the log file by defining the routine user_log_variables(), see m_user_methods.

Which variables the log file contains depends on the dimensionality of the run. The meaning of these variables is described below

name	meaning
it	simulation iteration
time	simulation time
dt	time step
v	estimate of streamer velocity (compared to last output)
sum(n_e)	integral of electron density
sum(n_i)	integral of first positive ion species
sum(charge)	integral of charge density (considering all species)
max(E) x y	maximum electric field + location
max(n_e) x y	maximum electron density + location
max(E_r) x y	maximum radial field + location
min(E_r)	minimum radial field
voltage	current applied voltage
ne_zmin, ne_zmax	Min/max location where the electron density exceeds a threshold
max(Etip) x y	Maximum electric field at streamer tip (tries to avoid boundaries) + location
wc_time	simulation wall-clock time (how long it has been running)
n_cells	number of grid cells used in simulation
min(dx)	minimum grid spacing
highest(lvl)	highest refinement level

2D planes

It is possible to extract output in a 2D plane using the following settings:

[plane]
    # Use this many pixels for plane data:
    npixels = 64 64

    # Relative position of plane maximum coordinate:
    rmax =  1.0000E+00  1.0000E+00

    # Relative position of plane minimum coordinate:
    rmin =  0.0000E+00  0.0000E+00

    # Names of variable to write in a plane:
    varname = 'e'

    # Write uniform output in a plane:
    write = F

1D lines

It is possible to extract output along a line using the following settings:

[lineout]
    # Use this many points for lineout data:
    npoints = 500

    # Relative position of line maximum coordinate:
    rmax =  1.0000E+00  1.0000E+00

    # Relative position of line minimum coordinate:
    rmin =  0.0000E+00  0.0000E+00

    # Write output along a line:
    write = F

It is also possible to extract such data from normal Silo files using the visit_lineout.py script in the tools folder.