They're making the assumption that the ions and electrons can be held outside of thermal equilibirium (and provide no evidence for this). In reality thermalisat

They're making the assumption that the ions and electrons can be held outside of thermal equilibirium (and provide no evidence for this). In reality thermalisation is likely to occur rapidly due to frequent collisions, once thermalised a normal Maxwell distribution will apply and Bremsstrahlung losses will return with a vengeance.