# get_ion_density_OML

plasmapy.diagnostics.langmuir.get_ion_density_OML(probe_characteristic: plasmapy.diagnostics.langmuir.Characteristic, probe_area: Unit('m2'), 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. :math: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 [mott-smith.langmuir-1926]:

$I_i \xrightarrow[T_i = 0]{} A_p n_i e \frac{\sqrt{2}}{\pi} \sqrt{\frac{e \left( V_F - V \right)}{m_i}}$

References

mott-smith.langmuir-1926

H. M. Mott-Smith, I. Langmuir, Phys. Rev. 28, 727-763 (Oct. 1926)