Spectroscopic Investigations of Nitrogen Loaded ECR Plasmas

Kuechler D.1, Ovsyannikov V.P.2, Ullmann F., Werner T., Zschornack G.
Technische Universitaet Dresden, Fachrichtung Physik, Institut fuer Kern- und Teilchenphysik, Mommsenstr. 13, D-01062 Dresden, Germany

Energy dispersive X-ray spectroscopy on ions in the plasma and magnetic q/A-analysis of the extracted ions were used to determine the plasma properties 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 the beam 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 and does not depend on the extraction and transmission properties of the ion extraction and transport system. Hence this method seems to be more accurate 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 differences for 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 loss currents inside the source.
Furthermore, the influence of different source operating regimes and of additional electron injection into the plasma were analysed, whereby the later one leads to a consideralbly higher output of highly charged ions. Especially efficient for reaching high currents of extracted ions is the use of so-called reflection mode electrons (RME). The basic idea here is that electrons travelling from the cathode of an electron gun in a strong axial field meet an anticathode potential (extractor potential), are reflected and go back to the cathode and so on. It can be supposed that the electrons make reflections up to the moment when the anode aperture will be fullfilled and the electrons will be collected on the anode electrode.

1permanent Address: CERN-PS-HP Division, CH-1211 Geneva 23
2permanent Address: Joint Institute for Nuclear Research, LHE, Moscow Region, RU-141980 Dubna

Presenting Author : Kuechler D.
Presentation : Poster
Tuesday Poster Session at 16:00