Beam-breakup and image-displacement instability coupling impedances in high-current electron-beam induction accelerators

It is noted that the beam breakup instability, together with its low-frequency limit, the image displacement instability, is a potentially serious issue for high-current electron induction accelerators. Earlier studies are generalized to obtain analytically derived coupling impedances for heavily loaded radial lines of arbitrary width, numerically determined coupling impedances for more complex gap geometries, and beam response to very low Q lines. In general, it is found that instability growth can be suppressed adequately for terawatt devices by suitable choices of gap shapes, line-termination impedances, and magnetic field strengths