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 probe array in the region from the scrape-off layer to just inside the last closed flux surface of neutral-beam-heated plasmas in a CHS. Radial profiles of magnetic fluctuation amplitude and their correlation length 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 length Lr _>; (average minor radius). The latter components, whose instability is not yet identified, have a relatively short correlation length r ∼ <a>/7.