Experimental reduction of beam-breakup instability growth by external cavity coupling in long-pulse electron-beam transport

Experiments have demonstrated the reduction of the beam-breakup (BBU) instability growth rate by coupling the main cavities, through which an electron beam passes, to identical dummy cavities. When seven of the ten main cavities are coupled, an average reduction of about 6 dB in BBU microwave growth, from 36 to 30 dB, is observed. This reduction is consistent with a simple mode coupling theory. The electron beam parameters are 750 kV, 210 A, 0.5 {μ}s, with solenoidal focusing of 3.4 kG.