ON A NEW INSTABILITY IN ELECTRON-POSITRON STORAGE RINGS (HEAD-TAIL EFFECT)

It is shown that a bunched electron or positron beam of a storage ring can become unstable because of an effect not previously considered; the instability is due to the regenerative effect introduced by synchrotron oscillations, which enhances the action on the beam of rapidly decaying electromagnetic signals excited by the beam itself on its surrounding media. The results obtained show that the effect can produce instabilities for small beam currents (in the milliampere range), and that it can be influenced and reduced by properly choosing some parameters of the storage ring. © 1969 Società Italiana di Fisica.