Estimating tokamak plasma transport scaling

Three Dimensional Electrostatic Gyrokinetic particle simulations of ion temperature gradient driven (ηi) instabilities have been carried out using parameters consistent with tokamak plasmas (e.g L-mode type discharges, etc.) to study scaling of the heat flux. The scaling for the heat flux is found to be gyro-Bohm. The authors start with a simple ion-electron plasma assuming an open-quotes adiabaticclose quotes response and no self-generated shear flow. In the linear stage of the simulation the poloidal wavenumber spectrum peaks near kyρs ∼ 0.5. In the nonlinear stage there is an energy cascade to longer poloidal wavelength modes (kyρs ∼ 0.2). This peak at the longer poloidal wavenumbers is more consistent with experimental observations of the poloidal wavenumber spectrum. Along with this energy cascade a change in the radial mode structure is observed. Self-generated shear flow is then included first using an open-quotes adiabaticclose quotes response for the electrons, and then a open-quotes nonadiabaticclose quotes response. This self-generated shear flow is found to reduce the level of the steady-state flux for the case of open-quotes adiabaticclose quotes electrons, while the effect appears to be less pronounced when a open-quotes nonadiabaticclose quotes response is used for the electrons. The inclusion of self-generated shear flow also changes the character of the energy cascade previously discussed. Finally, the effects of impurity ions are considered. Impurities are found to reduce the saturation level of the potential fluctuations (and the corresponding heat flux) depending on the concentration of the impurity species. Impurity heat and particle transport scaling are also presented for several impurity ion species