Gyrokinetic microinstabilities in ASDEX Upgrade edge plasmas

Results of linear gyrokinetic simulations of ASDEX Upgrade O. Gruber et al., Nucl. Fusion 39, 1321 (1999) edge plasmas, with experimentally determined geometry and input parameters, are presented. It is found that in the near-edge region, microtearing modes can exist under conditions found in conventional tokamaks. As one enters the steep-gradient region, the growth rate spectrum is dominated—down to very low wavenumbers—by electron temperature gradient modes. The latter tend to peak near the X-point(s) and possess properties which may explain the ratios of the density and temperature gradient scale lengths that have been observed in various experiments over the last decade.