Bremsstrahlung from thick targets and a diagnostic for electron energy distributions

The bremsstrahlung from solid material caused by runaway electrons may blur severely the bremsstrahlung that is recorded from gases or plasmas in orde r to determine the energy distribution of their hot electrons. The expressi ons for these emissions are presented in order to compare their characteris tics. Explanations are then given for an irregular feature observed at the tip of the spectrum for solid targets. More importantly, a type of diagnost ics of energy distribution functions is proposed, based on analysis of the bremsstrahlung emissivity from thick targets. II can be implemented on expe rimental setups by purposely inserting a well-defined solid target into the electron trajectories, and it is applied as an example to the electron bea m of microwave tubes. These diagnostics could also be taken advantage of to study runaway electrons hitting vessel walls.