Collective effects on DCI

Collective effects already seen on storage rings such as head-tail, phase instabilities, bunch lengthening have been observed again on DCI. A new collective effect on the betatron Q value seems to have been seen until now only on DCI and PETRA. A few other instabilities seem to have been observed only on DCI, sometimes for obvious reasons (the 4-beam instability for instance). Most single beam instabilities on DCI were cured although not completely understood. In one case systematic investigations hit on a difficulty: the instability was not always present in apparently similar experimental conditions. However adequate routines were always found to overcome the presence of non-cured instabilities and did not affect the operation of the machine for colliding beams. For this reason little time was spent on systematic studies of these instabilities and search for theoretical models, most of the effort until a few months being devoted to 4-beam studies. This paper presents some of the results obtained by the ORSAY Storage Ring Group on single beam and beam-beam behavior over the past few years