Current and current density limitations in existing electron storage rings

Storage rings dedicated for synchrotron light sources must show good beam performances in order to obtain high flux and brilliance. In particular bunch length, energy spread, beam intensity and transverse emittances have to satisfy special requirements. We intend here to briefly overview twenty years of experience obtained with small and medium size storage rings which were initially built as high energy physics facilities. The limiting effects will be extensively discussed by comparing theoretical models with systematic experimental studies. The possible means to remedy the inconveniences are also mentioned. (orig.)