Bremsstrahlung in hot plasmas with partially ionized atoms

Analytical bremsstrahlung results are obtained in an ionic radial potential whose screening constant lambda(i) due to the bound electrons can be parametrized in terms of the atomic number and the degree of ionization. By comparison with exact numerical results published for various incident electron energies E, the precision obtained for the cross sections is discussed in view of-determining the energy losses W, and the emissivity coefficients J and total power losses P for Maxwellian plasmas of temperature T. The discrepancy between the Born and Elwert-Born results for these three quantities is explained and the evolution with decreasing ionization from the Coulomb to the neutral case is studied. The relative reduction of the radiation with increasing screening is obtained satisfactorily in the simple approximations. Extrapolations using these reductions and tables of exact W's published for neutral atoms lead to ionic energy losses accurate to within 5%. However W, J, and P can all be determined successfully by direct simple expressions involving E/lambda(i)(2), h nu/lambda(i)(2), and/or kT/lambda(i)(2). The precision is at worst 25% and in most cases only a few percent, especially in the range of a few tens of keV.