collision_frequency¶

plasmapy.formulary.
collision_frequency
(T: Unit("K"), n: Unit("1 / m3"), species, z_mean: Unit(dimensionless) = <Quantity nan>, V: Unit("m / s") = <Quantity nan m / s>, method='classical') > Unit("Hz")¶ Collision frequency of particles in a plasma.
 Parameters
T (
Quantity
) – Temperature in units of temperature. This should be the electron temperature for electronelectron and electronion collisions, and the ion temperature for ionion collisions.n (
Quantity
) – The density in units convertible to per cubic meter. This should be the electron density for electronelectron collisions, and the ion density for electronion and ionion 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 nonclassical impact parameters.z_mean
is a required parameter ifmethod
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 straightline LandauSpitzer 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 ofCoulomb_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 the n_e, T, or V are not Quantities.
RelativityError – If the input velocity is same or greater than the speed of light.
 Warns
UnitsWarning
– If units are not provided, SI units are assumedRelativityWarning
– If the input velocity is greater than 5% of the speed of light.
Notes
The collision frequency is given by 1
\[ν = n σ v \ln{Λ}\]where \(n\) is the particle density, \(σ\) is the collisional crosssection, \(v\) is the interparticle velocity (typically taken as the thermal velocity), and \(\ln{Λ}\) is the Coulomb logarithm accounting for small angle collisions.
See Equation (2.14) in 2.
Examples
>>> from astropy import units as u >>> n = 1e19*u.m**3 >>> T = 1e6*u.K >>> species = ('e', 'p') >>> collision_frequency(T, n, species) <Quantity 70249... Hz>
References