Abstract: An electron cyclotron resonance ion source in which a plasma is confined in a magnetic configuration having a first group of coils located in the plane defined by the tight window of an ultra-high frequency injector and surrounding the latter, supplying the magnetic field creating and confining a plasma as well as a second group of coils supplied in counter-field compared with the first group and surrounding an ion extraction system. Ion extraction takes place in a magnetic field well below that corresponding to the cyclotron resonance. This ion source has numerous applications in the field of thin layer sputtering, microetching, ion implantation, accelerators, etc.