Dark current related breakdown mechanism.

High power tests of an 805 MHz pillbox cavity for the Muon Collider program have shown that the breakdown related damage increases and the sustainable gradient decreases with the application of a strong external magnetic field. To try to explain these results, a model of dark current associated breakdown was formulated and simulated with the Track3P code. The results show in general how the gradient could be reduced as function of magnetic field. This paper summarizes these studies to date. [ABSTRACT FROM AUTHOR]