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")[source]
Collision frequency of particles in a plasma.
Deprecated since version The:
collision_frequency
function has been replaced by the more generalSingleParticleCollisionFrequencies
class. To replicate the functionality ofcollision_frequency
, create aSingleParticleCollisionFrequencies
class and access theLorentz_collision_frequency
attribute.- 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 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 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 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.
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 (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>
See also