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In the ohmically heated W VII-A stellarator, the behaviour of which is similar to that of a medium sized tokamak, the additional shearless external rotational transform t(0) improves the stability properties and allows stationary and reproducible helium discharges with large amplitude tearing modes to be produced for t(0) values between 0.10 and 0.15. Discharges of this type are used to study, by means of Thomson scattering, the modification of electron temperature and density profiles by large amplitude tearing modes. The two-dimensional shapes of the profiles found experimentally can be attributed to the magnetic islands predicted by tearing mode theory. These shapes are further used to define an effective, locally enhanced radial transport coefficient in a one-dimensional heat transport code. In this way, the measured temperature profiles can be reproduced quite well and the energy confinement time of discharges with tearing mode activity can be predicted quantitatively. The transport model is used to investigate the explicit dependence of this transport coefficient on the plasma current and to study the importance of plasma current driven instabilities for the energy confinement in the W VII-A stellarator as well as in tokamaks.

Additional information

Authors: JAENICKE R, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE);W VII-A TEAM, Max-Planck-Institut fur Plasmaphysik, Garching bei Munchen (DE)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 28 (1988), No. 10, pp.1737-1750
Record Number: 198910136 / Last updated on: 1994-12-01
Original language: en
Available languages: en