Issues that are addressed in accordance with at least one presently preferred embodiment of the present invention, are: improvements upon the time it takes to physically swap degraders (done previously by hand); the safety involved in doing so, since the degraders become highly radioactive; possible improved energy resolution and beam stability if the accelerator can be left running continuously; and in-situ monitoring of beam current, beam position and stability. Particularly contemplated are methods and arrangements for changing degraders automatically, not manually, and in a safe manner.