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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 effects are taken into account to all orders. Nonadiabatic 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 effects of an electromagnetic perturbation on toroidal ion temperature gradient driven modes are studied, confirming the stabilization of these modes with increasing beta (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 or Alfvenic ion temperature gradient mode 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 effects of the Shafranov shift are addressed. (C) 2003 American Institute of Physics.

Global gyrokinetic particle simulations have been used to search tokamak configurations which are stable again st the ion-temperature-gradient - driven (ITG) modes commonly held responsible for the core anomalous ion heat transport. The stable configurations are-characterized by strongly reduced or reversed del B drifts on the low-field side. Since excellent transport properties have been observed in high beta p (poloidal beta) tokamak experiments, we conjecture, as a result of our simulations, that this may be due to the stabilization of ITG modes by the reduction of the del B drifts.

A new code, SEMAL, has been developed which solves the linearized Vlasov-Maxwell wave equations to all orders in Larmor radii. Arbitrary density and temperature profiles as well as non-uniform magnetic fields are considered in slab geometry. The vacuum regions adjacent to the plasma slab are limited by perfectly conducting walls and contain an antenna as an excitation source. The linear response is obtained by solving the system of one first-order and two second-order integro-differential equations using a non-polluting finite element discretization. The general equations in the Fourier space, derived in a new comprehensive way, and their inverse transform, using k(y) = 0, are described as well as the convergence and non-polluting properties of the method. We present the results concerning the influence of alpha particles on ICRF heating schemes for ITER, where we show that small alphas concentration can alter the steady-state operation envisaged with ICRF fast wave current-drive.

An explicit expression for the local power absorption density in a uniformly-magnetized slab plasma is derived from the Vlasov-Maxwell equations, taking into account density and temperature gradients. Using a transformation to Lagrangian coordinates, the kinetic flux of energy due to particle streaming can be separated in a suitable way from the actual power dissipation. Computations using this expression show how equilibrium gradients play a role in the modelling of low-frequency Alfven wave heating, and give a threshold below which the gradient effects are important in a medium-sized Tokamak.