Collisionless electron-temperature-gradient-driven ͑ETG͒ turbulence in toroidal geometry is studied via nonlinear numerical simulations. To this aim, two massively parallel, fully gyrokinetic Vlasov codes are used, both including electromagnetic effects. Somewhat surprisingly, and unlike in the analogous case of ion-temperature-gradient-driven ͑ITG͒ turbulence, we find that the turbulent electron heat flux is significantly underpredicted by simple mixing length estimates in a certain parameter regime (ŝ ϳ1, low ␣͒. This observation is directly linked to the presence of radially highly elongated vortices ͑''streamers''͒ which lead to very effective cross-field transport. The simulations therefore indicate that ETG turbulence is likely to be relevant to magnetic confinement fusion experiments. © 2000 American Institute of Physics. ͓S1070-664X͑00͒95905-6͔ bility criterion can be reformulated in terms of a critical e ϭL n /L T e if the density gradient is sufficiently steep. ͑This is *Paper FI16 Bull. Am. Phys. Soc. 44, 91 ͑1999͒. † Invited speaker.

The first toroidal, gyrokinetic, electromagnetic simulations of small scale plasma turbulence are presented. The turbulence considered is driven by gradients in the electron temperature. It is found that electron temperature gradient (ETG) turbulence can induce experimentally relevant thermal losses in magnetic confinement fusion devices. For typical tokamak parameters, the transport is essentially electrostatic in character. The simulation results are qualitatively consistent with a model that balances linear and secondary mode growth rates. Significant streamer-dominated transport at long wavelengths occurs because the secondary modes that produce saturation become weak in the ETG limit.

Some basic properties of collisionless, trapped-electron mode turbulence in tokamaks are investigated by means of massively parallel gyrokinetic Vlasov simulations. In particular, the spatial structure and wave number spectra of various fluctuating plasma quantities are presented and discussed. An analysis of several cross phase relations supports the view that the transport-dominating scales may be interpreted in terms of remnants of linear modes. In a few test cases, zonal flows are artificially suppressed, demonstrating that their influence on the transport level is small. Finally, the dependence of the latter on several plasma parameters is studied.

Under certain conditions, the electron heat transport induced by electron temperature gradient ͑ETG͒ streamers is sufficiently large and sensitive with respect to the normalized electron temperature gradient to represent a possible cause for electron temperature profile consistency ͑''stiffness''͒. Here, linear gyrokinetic simulations of toroidal ETG modes in tokamak core and edge plasmas are presented. An algebraic formula for the threshold of the linear instability is derived from the numerical solutions of the linear gyrokinetic equations which recovers previous analytical results in the appropriate limits.