Recombination

Recombination is an optional operator that adds neutral atoms formed by electron–ion recombination. It is enabled by including recombination under operators in [components]. It does not depend on the current neutral distribution, so it acts as a volumetric source and is added to the right-hand side like the source operator. In fact it reuses the same discretely normalized Maxwellian source machinery: at each spatial node, the velocity-space integral of the injected distribution equals the recombination rate exactly.

Two models are available, selected by model in [recombination].

`model = Janev1987`

The normalized volumetric rate is

\[ R_{\mathrm{rec}}(\mathbf{x}) = \hat n_e\,\hat n_i\,(n_0 t_0)\,\alpha_{\mathrm{rec}}(T_e), \]

where \(\hat n_e\), \(\hat n_i\) are the electron and ion densities in units of \(n_0 = 10^{18}\ \mathrm{m^{-3}}\), \(T_e\) is in eV, and \(\alpha_{\mathrm{rec}}\) is the radiative recombination coefficient of Janev et al. (1987). The new atoms are injected with the ion Maxwellian, using the ion temperature and drift from [i:init].

levels selects the coefficient:

1s (default): recombination into the ground state only.
total: the sum of the resolved 1s, 2s and 2p fits plus the high-\(n\) formula summed for \(n = 3,\dots,\) n_max (default 500).

This model requires species e and i:

[components]
species = n, e, i
operators = recombination

[recombination]
model = Janev1987
levels = total
n_max = 500

`model = prescribed`

The normalized volumetric rate is given directly as a profile, together with the Maxwellian of the injected atoms. Electron and ion species are not required.

[components]
species = n
operators = recombination

[recombination]
model = prescribed
rate = rec_rate
temperature = rec_temperature
ux = default_u
uy = default_u
uz = default_u

[profile:rec_rate]
type = constant
value = 0.1

[profile:rec_temperature]
type = constant
value = 2.0

Keys specific to one model are rejected for the other (for example rate with Janev1987, or levels with prescribed). See Inputs Reference for the full list.