Nonlocal diffusivity: Impact on transient transport studies

Nonlocal effects are observed in a number of transient transport studies in tokamaks and stellarators. In this paper some consequences of nonlocality are discussed on the basis of a heuristic model for the electron heat diffusivity (χe). The main consequence is the presence of an additional (‘‘missing’’) heating power term (p̃χ) in the heat transport equation. Suitable combinations of p̃χ and modulated power profiles should give rise to detectable effects in modulated heating experiments such as those planned on the Frascati Tokamak Upgrade (FTU) [R. Andreani et al., in Fusion Technology, Proceedings of the 16th Symposium, London, 1990, edited by B. E. Keen, M. Huguet, and R. Hemsworth (Elsevier Science, Amsterdam, 1991), Vol. 1, p. 218]. Failure to properly include p̃χ effects (if present) can lead to an overestimate of χe from heat wave propagation analysis.