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Abstract

Arrays of edge magnetic coils and an insertable magnetic probe have been used to study the behaviour of the magnetic fluctuations in the HBTX1A Reversed Field Pinch. EDGE COILS: In the sustainment phase of the discharge poloidal arrays of edge coils show that the superficially random fluctuations can be attributed almost entirely to global modes of poloidal mode number m = 0 and 1 provided account is taken of the toroidal distortion of these instabilities. INSERTABLE PROBE: A statistical method for determining the radial amplitude distributions of instabilities is presented. This is used to analyse probe data from which it is possible to distinguish three types of instability. At low frequencies (4-20 kHz) the dominant internal fluctuations are to be associated with the global m = 1, /n/ approximately equal 10 resistive modes seen by the edge coils. At high frequencies (>30 kHz) the local turbulence dominates over the global modes. Finally, at about 1/4 the peak power of the dominant global modes and with similar frequency dependence, an m = 1 mode with some ideal characteristics is observed. Stability calculations show that ideal modes destabilized by a resistive shell or with growth rates reduced by a resistive liner would have the same radial structure and timescales as this mode.

Additional information

Authors: BROTHERTON RATCLIFFE D CULHAM LABORATORY, ABINGDON, OXON (UK), CULHAM LABORATORY, ABINGDON, OXON (UK)
Bibliographic Reference: PH.D. THESIS OF THE UNIVERSITY OF LONDON, EGHAM, ROYAL HOLLOWAY COLLEGE (UK), 1984
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