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P: Plasmaphysik
P 6: Discharges
P 6.5: Vortrag
Donnerstag, 5. April 2001, 17:40–17:55, 2053
Isotope effect in an ECR ion source in mixtures of 15N/14N — •K. Wiesemann, Y. Kawai, A. Nadzeyka, and D. Meyer — Experimentalphysik, insbes. Gaselektronik, Ruhr-Universität Bochum, D-44801 Bochum
We have investigated the so-called isotope anomaly in an ECR (Electron Cyclotron Resonance) ion source in mixtures of 14N and 15N. The ratio of the extracted currents I(15Nq+)/I(14Nq+) increases with increasing q+. This trend, however, gradually disappears when the partial pressure of 15N is increased at constant total pressure. The isotope effect also disappears when helium is added like in 17O/18O mixtures. Further, it disappears if the endplate on the gas inlet side of the discharge chamber is biased negatively. Usually, the isotope anomaly is discussed in terms of the No-dqion coolingNo-dq model, which is based on the mass dependence of thermal particle transport. However the No-dqion coolingNo-dq model can not give a quantitative explanation especially of the new effects reported here. Therefore we suggest a new model, which considers ion heating by low frequency plasma noise.