⁵For a plasma with a single fully ionized impurity, the fast electron bremsstrahlung may be determined using the effective charge Z_eff, from which n_s may be evaluated, as shown in Sec. ***. However, when heavy impurities partially ionized are present in the plasma, their densities n_s = ∑ _s^′n_ss^′ must be determined from an impurity transport code, which gives the contribution of all different states. Indeed, when kinetic energies of the fast electrons are much larger than the fundamental Rydberg state, only the charge state of the nucleus must be considered for the bremsstrahlung calculations, since screening effects with bounded electrons is negligible.