Instabilities in storage rings

The last generation of storage rings is designed to operate with low emitta nces (longitudinal and transverse) and rather high currents. Performances o f these machines are limited by the collective effects. The interaction of a beam with the surrounding walls produces parasitic fields which, acting b ack on the beam, can lead to instability phenomena. Other instability effec ts are known, where the beam interacts with foreign (ions, electrons, dust, etc.). Recently, new types of instabilities have drown the attention of ac celerator physicists. Here pre give a short review of the instability effec ts and discuss their basic features.