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The energy confinement time tau(E) for ohmically heated discharges in FT has been studied over a wide range of plasma parameters. It is found to increase linearly with the average density n(e) below 1 x 1.0 E14/cm3 and to saturate at higher densities. The analysis of the experimental data shows that, at the same density at which saturation is reached, Z(eff) becomes nearly equal to 1 and the electron and ion temperature become nearly equal. The saturated tau(E) shows a strong isotope effect with a reduction of a factor of 1.5 when operating in hydrogen. The sawteeth period is closely correlated with tau(E) and displays the same saturated behaviour and isotope effect. The ion thermal diffusivity X(i) is found to be compatible with neoclassical theory up to the maximum density, but a neoclassical multiplier of 3 would only fit the highest n(e) data. X(e) first decreases with the inverse of n(e) but remains nearly constant in the saturated region. The ohmic saturation in FT seems, therefore, to be caused primarily by electron transport.

Additional information

Authors: ALLADIO F ET AL., ENEA, Centro Ricerche Energia Frascati, Roma (IT)
Bibliographic Reference: Report: RT/NUCL/90/40 EN (1991) 11 pp.
Availability: Available from Servizio Studi e Documentazione, ENEA, Centro Ricerche Energia Frascati, C.P. 65-00044 Frascati, Roma (IT)
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