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In a Tokamak fusion plasma, the induced plasma current and the external magnetic field coils create an appropriate magnetic field structure for confinement and stability of the plasma. The Motional Stark Effect diagnostic (MSE) is the main tool for the determination of the toroidal current density and the magnetic field configuration inside a Tokamak fusion plasma.
Within this work, the MSE data acquisition in ASDEX Upgrade was improved towards a real-time diagnostic. This real-time MSE diagnostic shall be used for the current profile, j, control during the experiment.
During the analysis of structures in the MSE measurements, a central region in the plasma without current density and without confining poloidal magnetic field was found, a so-called 'current hole'. In 'current hole' scenarios, a strong non-inductive current off-axis (e.g. bootstrap current) forms/maintains the 'current hole'.
The optimization of the bootstrap current is part of the 'advanced tokamak' studies since the bootstrap current is one candidate to replace at least partially the toroidal current produced with the transformer.
There are considerations in the international research community to develop the 'current hole' scenarios with the strong non-inductive current further towards a steady state scenario with reduced inductive current. The study of 'current holes' is also an important issue for predicting current profile evolution in next step fusion facilities like ITER, with high current diffusion time in scenarios with strong non-inductive current.
In the present work, the equilibrium reconstruction of 'current holes' are presented along with results of the current diffusion analysis.

Additional information

Authors: MERKL D, Max-Planck-Institut für Plasmaphysik, IPP-EURATOM Association, Garching (DE)
Bibliographic Reference: Garching: Max-Planck-Institut für Plasmaphysik, 2004. 98 pp Free of charge
Availability: The document can be downloaded at:
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