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P: Plasmaphysik

P 6: Discharges

P 6.5: Talk

Thursday, April 5, 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(¹⁵N^q+)/I(¹⁴N^q+) 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.