Spectroscopic Investigation of Nitrogen Loaded ECR Plasmas

Energy dispersive X-ray spectroscopy on ions in the plasma and magnetic q/A-analysis of the extracted ions were used to determine the plasmaproperties of nitrogen loaded ECR plasmas.As the beam expands from a limited plasma region and the ion extraction process alters the plasma properties in the extraction meniscus thebeam composition does not correspond to the bulk plasma composition. The analysis of measured spectra of characteristic X-rays delivers a method to determine the ion charge state distribution and the electron energy distribution inside the plasma and does not alter the plasma anddoes not depend on the extraction and transmission properties of the ion extraction and transport system. Hence this method seems to be moreaccurate than the traditional magnetic analysis and allows to analyse different plasma regions.A comparison between ion charge state distributions determined from X-ray spectra and such from q/A-analysis shows significant differencesfor the mean ion charge states in the source plasma and for the extracted ion beam.The use of a pin-hole camera allows to analyse the particle distribution inside the source chamber and give a clear picture of electron losscurrents inside the source.Furthermore, the influence of different source operating regimes and of additional electron injection into the plasma were analysed, wherebythe later one leads to a consideralbly higher output of highly charged ions. Especially efficient for reaching high currents of extracted ions is theuse of so-called reflection mode electrons (RME). The basic idea here is that electrons travelling from the cathode of an electron gun in a strongaxial field meet an anticathode potential (extractor potential), are reflected and go back to the cathode and so on. It can be supposed that theelectrons make reflections up to the moment when the anode aperture will be fullfilled and the electrons will be collected on the anodeelectrode.