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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.

Additional information

Authors: GIANNONE L, Max-Planck-Institut für Plasmaphysik, Garching-bei-München (DE);ASDEX, Max-Planck-Institut für Plasmaphysik, Garching-bei-München (DE);NI, Max-Planck-Institut für Plasmaphysik, Garching-bei-München (DE);ECRH AND PELLET TEAMS, Max-Planck-Institut für Plasmaphysik, Garching-bei-München (DE)
Bibliographic Reference: Report: IPP III/138 EN (1989)
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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