Validity of Quasi-Linear Transport Model

In order to gain reliable predictions on turbulent fluxes in tokamak plasmas, physics based transport models have to be improved. On a confinement time scale, nonlinear gyrokinetic electromagnetic simulations for all species are still too costly in terms of computing time. On the other hand, interestingly, quasi-linear approximation seems to retain the relevant physics for fairly reproducing both experimental results [1, 2] and nonlinear gyrokinetic simulations [3, 4, 5, 6]. Quasi-linear fluxes are made of two parts, the quasi-linear weight and the saturated squared electrostatic potential. The first one is shown to follow well nonlinear predictions; the second one is based on both nonlinear simulations and turbulence measurements. The resulting quasi-linear fluxes are shown to agree with the nonlinear ones when varying various dimensionless parameters such as the ion to electron temperature ratio, the collisionality ν* and the temperature gradients, ranging from Ion Temperature Gradient (ITG) to Trapped Electron Modes (TEM) turbulence.