get_ion_density_OML

plasmapy.diagnostics.langmuir.get_ion_density_OML(probe_characteristic, probe_area, gas, visualize=False, return_fit=False)

Implement the Orbital Motion Limit (OML) method of obtaining an estimate of the ion density.

Parameters:

• probe_characteristic (Characteristic) – The swept probe characteristic that is to be analyzed.
• probe_area (Quantity) – The area of the probe exposed to plasma in units convertible to m^2.
• gas (Quantity) – The (mean) mass of the background gas in atomic mass units.
• visualize (bool, optional) – If True a plot of the OML fit is shown. Default is False.
• return_fit (bool, optional) – If True the parameters of the fit will be returned in addition to the ion density. Default is False.

Returns:

n_i_OML – Estimated ion density in m^-3.

Return type:

Quantity

Notes

The method implemented in this function holds for cylindrical probes in a cold ion plasma, ie. T_i = 0 eV. With OML theory an expression is found for the ion current as function of probe bias independent of the electron temperature:

\[I = A_p n e \frac{\sqrt{2}}{\pi} \left( \frac{|eV_b|}{m_i} \right)^{1/2}\]