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Internal disruptions in tokamak plasma often exhibit an m=1 poloidal mode structure prior to the collapse. In this paper tomographic reconstructions of such m=1 modes are analyzed with a new method, based on magnetohydrodynamic (MHD) invariants computed from the two-dimensional emissivity profiles, which quantifies the amount of profile flattening not only after the crash but also during the precursor oscillations. The results are interpreted by comparing them with two models which simulate the measurements of m=1 redistribution by soft x-ray emissivity prior to the sawtooth crash. One model is based on the magnetic reconnection model of Kadomtsev. The other involves ideal MHD motion only. In cases where differences in magnetic topology between the two models cannot be seen in the tomograms, the analysis of profile flattening has an advantage. The analysis shows that in Rijnhuizen Tokamak Project (RTP) the clearly observed m=1 displacement of some sawteeth requires the presence of convective ideal MHD motion, whereas other precursors are consistent with magnetic reconnection of up to 75% of the magnetic flux within the q=1 surface.

Additional information

Authors: TANZI C P, FOM-Instituut voor Plasmafysica Rijnhuizen, Nieuwegein (NL);DE BLANK H J,
Bibliographic Reference: Article: Physics of Plasmas, Vol. 4 (1997) No. 3, pp. 696-708
Record Number: 199710964 / Last updated on: 1997-08-14
Original language: en
Available languages: en