Gyroaveraged equations for both the gyrokinetic and drift‐kinetic regimes

The regime of validity of nonlinear gyrokinetic equations is extended to cover uniformly both the usual drift‐kinetic and gyrokinetic regimes through the use of an expansion in the parameter e∼(ρ/λ⊥)e(φ−v∥ Az/c)/T. Here, ρ is the gyroradius, λ⊥ is the scale length of the electrostatic and parallel magnetic potentials φ and Az, c is the speed of light, and T is the temperature. This is made possible by a preparatory split of the potentials into gyrophase‐dependent and independent parts. For nonlinear fluctuations saturated at mixing‐length levels (e.g., with eφ/T∼λ⊥ /L, where L is the equilibrium scale length), e is of order ρ/L for all scales λ⊥ ranging from ρ to L, and is therefore small in plasmas of fusion interest.