Ionization

Ionization is an optional operator in GUERNICA that removes neutrals from the distribution function. In the current implementation, it acts as a linear loss term of the form

\[ \left.\frac{\partial f_n}{\partial t}\right|_{\mathrm{ion}} = -\nu f_n, \]

where \(f_n\) is the neutral distribution function and \(\nu\) is the ionization rate. In code, this is applied pointwise at each element and velocity state as a sink term added to the right-hand side.

Although the operator class is written to accept a general MFEM coefficient for \(\nu\), project it onto the finite element space, and pack the resulting nodal values for device use, the current input-file validation only allows the constant ionization model. In practice, this means the present user-facing configuration corresponds to a spatially constant ionization rate set by nu0.

Ionization is enabled through [components]. To use it, operators must include ionization, and species must include both n and e. The neutral species n is the distribution that evolves in time, while the electron species e is included as a required background species for this operator.

A minimal ionization setup therefore looks like:

[components]
species = n, e
operators = ionization

[ionization]
model = constant
nu0 = 10.0