Transport studies in TJ-I tokamak from steady and perturbative methods

Transport understanding is an essential task for the development of a future tokamak fusion reactor. In a general formulation, the dependence of particle and electron energy fluxes on density and temperature gradients, may be written as: Γ=-D∇n - DTn ∇T/T - nV, q=Q-5/2ΓT=-χnT∇n-χn∇T-nTU where both fluxes are related to both gradients, and the particle and energy pinches V and U may depend on any other force as could be the parallel electric field. The transport coefficients must be expected to be functions of local plasma parameters such as B, q, n, T, ∇n, ∇T, ... etc. This means that the fluxes may be non-linear functions of the gradients. Transport analysis in the steady state gives values, from experimental data, for fluxes and gradients. This is not enough to determine the values of the six transport coefficients. A perturbative experiment, such as the simultaneous measurement of density and temperature pulses induced by a sawtooth collapse, give us the incremental transport coefficients or the derivatives of the fluxes with respect to the gradients. By making a coupled analysis of both pulses, we can obtain values for the four derivatives: ∂Γ∂∇n, ∂Γ/∂∇T, ∂q/∂∇n and ∂q/∂∇T. The combination of both steady and perturbative studies in discharges with different plasma parameters could give us a better picture of transport processes in a tokamak. (author) 6 refs., 5 figs