Plasma ion mass spectrometry in the boundary of the DITE Tokamak

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Abstract
Very limited diagnostic techniques are available for the study of flux and charge state distribution of impurities and plasma ions in the Tokamak scrape-off layer. The author describes an in situ plasma ion mass spectrometer (PIMS) which provides real time information on the charge-to-mass ratio of the ions in the scrape-off layer. The instrument, which is being developed on the DITE Tokamak, is based on the cycloidal focusing system and achieves a mass resolution of approximately=20. Results are presented which demonstrate the performance of the device. The observed charge state distributions are compared with theoretical predictions and an explanation for the near equality of the oxygen and carbon fluxes is presented.