# collision_frequency

plasmapy.formulary.collisions.frequencies.collision_frequency(T: Unit("K"), n: Unit("1 / m3"), species, z_mean: ~numbers.Real = nan, V: Unit("m / s") = <Quantity nan m / s>, method='classical') -> Unit("Hz")

Note

The collision_frequency function has been replaced by the more general SingleParticleCollisionFrequencies class. To replicate the functionality of collision_frequency, create a SingleParticleCollisionFrequencies class and access the Lorentz_collision_frequency attribute.

Collision frequency of particles in a plasma.

Parameters
• T (Quantity) – Temperature in units of temperature. This should be the electron temperature for electron-electron and electron-ion collisions, and the ion temperature for ion-ion collisions.

• n (Quantity) – The density in units convertible to per cubic meter. This should be the electron density for electron-electron collisions, and the ion density for electron-ion and ion-ion collisions.

• species (tuple) – A tuple containing string representations of the test particle (listed first) and the target particle (listed second).

• z_mean (Quantity, optional) – The average ionization (arithmetic mean) of a plasma for which a macroscopic description is valid. This parameter is used to compute the average ion density (given the average ionization and electron density) for calculating the ion sphere radius for non-classical impact parameters. z_mean is a required parameter if method is "ls_full_interp", "hls_max_interp", or "hls_full_interp".

• V (Quantity, optional) – The relative velocity between particles. If not provided, thermal velocity is assumed: $$μ V^2 \sim 2 k_B T$$ where $$μ$$ is the reduced mass.

• method (str, optional) – The method by which to compute the Coulomb logarithm. The default method is the classical straight-line Landau-Spitzer method ("classical" or "ls"). The other 6 supported methods are "ls_min_interp", "ls_full_interp", "ls_clamp_mininterp", "hls_min_interp", "hls_max_interp", and "hls_full_interp". Please refer to the docstring of Coulomb_logarithm for more information about these methods.

Returns

freq – The collision frequency of particles in a plasma.

Return type
Raises
• ValueError – If the mass or charge of either particle cannot be found, or any of the inputs contain incorrect values.

• UnitConversionError – If the units on any of the inputs are incorrect.

• TypeError – If any of n_e, T, or V is not a Quantity.

• RelativityError – If the input velocity is same or greater than the speed of light.

Warns

Notes

The collision frequency (see Ch. 5 of Chen [2016]) is given by

$ν = n σ v \ln{Λ}$

where $$n$$ is the particle density, $$σ$$ is the collisional cross-section, $$v$$ is the inter-particle velocity (typically taken as the thermal velocity), and $$\ln{Λ}$$ is the Coulomb logarithm accounting for small angle collisions.

See Equation (2.14) in Callen [n.d.].

Examples

>>> import astropy.units as u
>>> n = 1e19 * u.m**-3
>>> T = 1e6 * u.K
>>> species = ('e', 'p')
>>> collision_frequency(T, n, species)
<Quantity 70249... Hz>