Global-Gyrokinetic Study of Finite fl Eects on Linear Microinstabilities

Electromagnetic microinstabilities in tokamak plasmas are studied by means of a linear global eigenvalue numerical code. Ion dynamics is described by the gyrokinetic equation, so that finite ion Larmor radius eects are taken into account to all orders. Non adiabatic electrons are included in the model, with passing particles described by the drift-kinetic equation and trapped particles through the bounce averaged drift-kinetic equation. A large aspect ratio plasma with circular shifted surfaces is considered for the numerical implementation. The eects of an electromagnetic perturbation on toroidal Ion Temperature Gradient driven (ITG) modes are studied, confirming the stabilization of these modes with increasing fl (parameter identifying the ratio of the plasma pressure to the magnetic pressure). The threshold for the destabilization of an electromagnetic mode, the so-called kinetic ballooning mode (KBM) or Alfvenic Ion Temperature Gradient mode (AITG) is identified. Moreover, owing to the global formulation, the radial structure of these electromagnetic modes is observed for the first time. Finally, the contributions of trapped electron dynamics and the eects of the Shafranov shift are addressed.