Single beam instabilities in DORIS

In the electron- and positron rings of DORIS, strong reverse and longitudinal single beam instabilities caused current limitations. The most severe transverse and longitudinal instabilities were induced by excitation of higher modes in the rf-cavities. When these instabilities were cured by damping the higher cavity modes, the thresholds for these types of instabilities were greatly increased. The origin of the remaining transverse and longitudinal instabilities is not yet understood. The thresholds of these instabilities were increased by Landau-damping and by changing the betatron- and synchrotron frequencies from bunch to bunch. The head-tail effect was observed at high peak currents and was cured by compensating the chromaticity. In the electron ring, a transverse instability is induced by the ions. Ion clearing, in combination with some vacuum improvements, is sufficient to avoid this instability. (auth)