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 order to determine the energy distribution of their hot electrons. The expressions for these emissions are presented in order to compare their characteristics. Explanations are then given for an irregular feature observed at the tip of the spectrum for solid targets. More importantly, a type of diagnostics of energy distribution functions is proposed, based on analysis of the bremsstrahlung emissivity from thick targets. It can be implemented on experimental setups by purposely inserting a well-defined solid target into the electron trajectories, and it is applied as an example to the electron beam of microwave tubes. These diagnostics could also be taken advantage of to study runaway electrons hitting vessel walls.