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A method of measuring the q-profile (slightly off the centre) in a plasma is described. Radially injected molecular neutrals are ionised in the plasma and rotate according to the local magnetic field. After dissociation the neutral atom carries the information on the velocity of the molecular ion at the time of dissociation to a neutral particle analyser. This information can be used to calculate the local field. The production and penetration of molecular beams are discussed as well as the requirements to be met by the beam and analyser. Also discussed are the possible influence of neutral atom beams and their relevance to the same type of measurement. It is shown that the Shafranov shift can be determined by suitable choices of the injection and detection geometries. The method seems to be especially suited to measuring the time variation of local q-values with a time resolution of about 1 ms. Although the penetration of the particles depends on the plasma conditions, the quantity measured by this method only depends on the local field ratio. The method could also be applied in large plasma experiments the size of JET, and an accuracy in measuring q of better than or about 10% may be achieved.

Additional information

Authors: HERRMANN W, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP1/249 EN (1989)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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