Noninvasive measurement of electron-beam size with diamagnetic loops

Diamagnetic loops can be used as a noninvasive method for measurements of beam size in electron beam accelerators that use solenoidal magnetic transport. A comprehensive theory for interpreting data from a diamagnetic loop is developed. It is shown that the change in flux through a diamagnetic loop can be simply related to the rms beam radius to high accuracy, regardless of the details of the current profile, when the ratio of beam current to Alfven current Ib/IA is small. The difficulty in making this measurement lies in the fact that the diamagnetic-loop signal is also small to the same order