Programmer’s Reference

Copyright 2018

Sigvald Marholm <marholm@marebakken.com> Diako Darian <diako.darian@gmail.com>

This file is part of langmuir.

langmuir is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

langmuir is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with langmuir. If not, see <http://www.gnu.org/licenses/>.

langmuir.analytical.OML_current(geometry, species, V=None, eta=None, normalization=None)

Current collected by a probe according to the Orbital Motion Limited (OML) theory. The model assumes a probe of infinitely small radius compared to the Debye length, and for a cylindrical probe, that it is infinitely long. Probes with radii up to 0.2 Debye lengths (for spherical probes) or 1.0 Debye lengths (for cylindrical probes) are very well approximated by this theory, although the literature is diverse as to how long cylindrical probes must be for this theory to be a good approximation.

geometry: Plane, Cylinder or Sphere

Probe geometry

species: Species or array-like of Species

Species constituting the background plasma

V: float or array-like of floats

Probe voltage(s) in [V]. Overrides eta.

eta: float or array-like of floats

Probe voltage(s) normalized by k*T/q, where q and T are the species’ charge and temperature and k is Boltzmann’s constant.

normalization: ‘th’, ‘thmax’, None

Wether to normalize the output current by, respectively, the thermal current, the Maxwellian thermal current, or not at all, i.e., current in [A/m].

float if voltage is float. array of floats corresponding to voltage if voltage is array-like.

langmuir.analytical.jacobsen_density(geometry, biases, currents, species=Species(q=-1.602176634e-19, m=9.1093837015e-31, n=100000000000.0, T=1000))

Density computed according to the slope in current squared versus voltage (the Jacobsen-Bekkeng method). This assumes that OML theory for a cylindrical probe is exact.

geometry: Cylinder

Probe geometry

biases: array-like of floats

Probe bias voltages [V] with respect to some common reference

currents: 2D array-like of floats

Current measurements. currents[i,j] is sample i, probe current j

species: Species

The attracted species. The density and temperature in the species object is disregarded by this function.

Array of computed densities, one element for each row in currents.

langmuir.analytical.normalization_current(geometry, species)

Returns the normalization current for the given species and geometry. The normalization current is the current the species would have contributed to a probe at zero potential with respect to the background plasma due to random thermal movements of particles, if the species had been Maxwellian.

geometry: Plane, Cylinder or Sphere

Probe geometry

species: Species or array-like of Species

Species constituting the background plasma

float

langmuir.analytical.thermal_current(geometry, species, normalization=None)

Returns the thermal current.

geometry: Plane, Cylinder or Sphere

Probe geometry

species: Species or array-like of Species

Species constituting the background plasma

float