ECR ion sources today Physics, performance and technology

ECR ion sources are now widely used in accelerators because of their ability to produce highly charged heavy ion beams. This article is an attempt to give an overview of the research and development devoted to these devices. The understanding of the physics of these sources (and especially of their plasma), although still partial, is steadily improving; the state of the art of the present knowledge on ECRIS is described in the first part of the paper. In the second part the technological aspects related to ECRIS are presented. In the third part of the article the various existing sources, their design and performances, are surveyed. At last the trends for future developments are examined.