Thermal bremsstrahlung

Thermal bremsstrahlung is free-free electromagnetic radiation from the acceleration of charged particles during Coulomb encounters in a thermal plasma. Its frequency-integrated emissivity in a fully ionized, nonrelativistic plasma scales approximately as $n_e{n}_i{T}^{1/2}$.

The Gaunt factor is the dimensionless quantum correction to a classical free-free radiation calculation. Its weak temperature and frequency dependence modifies the approximate thermal bremsstrahlung scaling; a frequency-averaged value appears in the bolometric cooling coefficient.