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On the basis of the quasilinear theory of current drive in tokamaks by lower hybrid waves, a velocity diffusion process is introduced for electrons that are not Landau resonating with the waves. This effect is connected to the time dependence of the wave field autocorrelations, which can be determined by nonlinear terms (only postulated here) or by the geometric effect of a sharp wave beam of finite toroidal width. In both cases the role of nonresonant electron velocity diffusion is important in evaluating the driven current and the absorbed power correctly, as it may fill the gap in velocity space between bulk and resonant tail electrons. It also implies the presence of a fast REF-runaway electron tail above the Landau resonance. This tail requires a treatment including relativistic effects, as well as 2-D velocity space and cross field transport of fast electrons, but preliminary considerations indicate that it does not depend significantly on the wave spectrum nor on the accessibility limit. Finally, the temperature scaling of the current drive efficiency is found to be different from the classical result obtained in the usual quasilinear theory.

Additional information

Authors: SANTINI F, ENEA, Centro Ricerche Energia Frascati, Roma (IT)
Bibliographic Reference: Report: RT/NUCL/90/37 EN (1991) 24 pp.
Availability: Available from Servizio Studi e Documentazione, ENEA, Centro Ricerche Energia Frascati, C.P. 65-00044 Frascati, Roma (IT)
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