The Beam Breakup Instability in Pulsed Transmission Line Linear Accelerators

The transverse Beam Breakup Instability (BBI) can result in reduced pulse length in linear accelerators. A brief summary of the instability mechanism and a gain formula are presented. Test bench measurements of the two relevant parameters, transverse shunt impedance Z
₁
, and cavity Q have been made. These measurements illustrate the importance of transmission line dielectric and cavity geometry to the gain. Results indicate that Q may vary from 10 - 75, and that Z
₁
/Q is in the range 4 - 70 Ω.