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The scaling of the energy confinement time with plasma density and current was investigated for ohmically heated tokamak discharges in ASDEX. The linear dependence of the confinement time is maintained in the high density improved ohmic confinement (IOC) regime with peaked density profiles. The peaking of the radial density profile can be brought about by reducing the net power flow through the plasma surface thereby effecting a reduction of the edge density. Tailoring of the radiation profile with the addition of low-Z impurities, e.g. neon, gives access to the IOC regime under conditions where otherwise the degraded saturated ohmic confinement (SOC) behaviour prevails. The energy confinement time increases with current and decreases with heating power also in ohmic discharges as shown by a statistical analysis. But with the intrinsic coupling between power and current, both relationships cancel and the confinement time becomes independent of P(oh) and I(p). The two most prominent features of ohmic confinement can therefore be explained on the basis of simple physical models.

Additional information

Authors: BESSENRODT-WEBERPALS M, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);MCCORMICK K, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);THE ASDEX TEAM ET AL., Max-Planck-Institut für Plasmaphysik, Garching bei München (DE);TSOIS N, N.R.C.N.S., Democritos, Athens (GR)
Bibliographic Reference: Report: IPP III/161 EN (1990) 42 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
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