MEASUREMENT OF MAGNETIC-FIELD FLUCTUATIONS NEAR PLASMA EDGE WITH MOVABLE MAGNETIC PROBE ARRAY IN CHS HELIOTRON TORSATRON/

Magnetic fluctuations are measured with a newly developed movable prob e array in the region from the scrape-off layer to just inside the las t closed flux surface of neutral-beam-heated plasmas in a CHS. Radial profiles of magnetic fluctuation amplitude and their correlation lengt h are derived for low frequency (less than 40 kHz) coherent components with low mode number and for relatively high frequency (greater than 60 kHz) coherent components are inferred to an ideal interchange mode excited in the plasma interior and have a large radial correlation len gth L-r greater than or equal to[a] (average minor radius). The latter components, whose instability is not yet identified, have a relativel y short correlation length L-r approximate to[a]/7. (C) 1997 Elsevier Science S.A.