EXPERIMENTAL OBSERVATIONS OF BROADBAND MAGNETIC FLUCTUATIONS IN ASDEX
Broadband magnetic fluctuations in ASDEX were previously studied with Mirnov coils fixed at a distance of 12 cm from the separatrix. This report documents the extension of that work. The magnetic probe is mounted on a pneumatically driven manipulator. This allows the radial position of the probe to be scanned during the discharge, or a stationary probe to be fixed at a chosen distance from the separatrix. Magnetic probes in major tokamaks have been usually positioned close to the vessel wall and strongly shielded. Signal-to-noise ratios then deteriorate above a few hundred kiloHertz. The probe system on ASDEX can provide a measurable response at 1 MHz in Ohmic discharges. Measurements on ASDEX indicate that edge plasma conditions play a role in determining the level of broadband magnetic fluctuations. This was inferred from observations of a perturbation of the magnetic fluctuation amplitude coincident with the arrival of the heat pulse induced by a sawtooth crash. The measurement of a mode with m about 25 in the toroidal field component of the fluctuating magnetic field in the vicinity of the separatrix in ohmic discharges and the behaviour of this component during the H-mode supports this hypothesis.
Bibliographic Reference: REPORT: IPP III/138 (1989) AVAILABLE FROM MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, 8046 GARCHING BEI MUENCHEN (DE)
Record Number: 1989128017400 / Last updated on: 1990-11-09
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