langmuir 0.6.3

Functions for work on Langmuir probe theory

Programmatically accessible current-voltage characteristics for ideal and non-ideal Langmuir probes. See documentation on ReadTheDocs.

Installation

Install from PyPI using pip (preferred method):

pip install langmuir

Or download the GitHub repository https://github.com/langmuirproject/langmuir.git and run:

python setup.py install

Getting Started

The Langmuir library contains a collection of functions that compute the current collected by a Langmuir probe according to various theories and models. These functions take as arguments the probe geometry, for instance Cylinder, and a plasma, where a plasma may consist of one or more Species.

As an example, consider a 25mm long cylindrical probe with radius 0.255mm. The plasma consists of electrons and singly charged oxygen ions, both with a density of 1e11 and a temperature of 1000K. The current-voltage charactersitic according to OML theory is easily computed and plotted:

>>> from langmuir import *
>>> import numpy as np
>>> import matplotlib.pyplot as plt

>>> plasma = []
>>> plasma.append(Species('electron' , n=1e11, T=1000))
>>> plasma.append(Species(amu=16, Z=1, n=1e11, T=1000))

>>> Vs = np.linspace(-2, 2, 100)
>>> Is = OML_current(Cylinder(r=0.255e-3, l=25e-3), plasma, Vs)

>>> fig = plt.figure()
>>> ax = fig.add_subplot(111)

>>> ax.plot(Vs, -Is*1e6)
>>> ax.set_xlabel(r'$V_{\mathrm{p}} [\mathrm{V}]$')
>>> ax.set_ylabel(r'$I_{\mathrm{p}} [\mathrm{\mu A}]$')
>>> ax.grid(True)
>>> plt.show()

Notice that the characteristic includes all regions (ion saturation, electron retardation and electron saturation), and do not rely on approximations to the OML theory requiring the voltage to be within a certain range. What’s more, it’s easy to take into account for instance finite-radius effects, by replacing OML_current() with finite_radius_current().