Variational approach to radiofrequency waves in magnetic fusion devices

Magnetic fusion plasmas feature two major classes of low frequency electromagnetic oscillations: waves in the ion cyclotron range of frequencies (ICRFs) constitute a well established method employed for plasma heating and current drive, whereas waves in the Alfven range of frequencies naturally occur in the form of modes in close interaction with fast particles. The propagation of these waves is characterized by significant space-dispersion, making it necessary to incorporate non-local effects in the global kinetic full-wave codes which are often employed for their simulation. We present here a variational approach to this problem, which has the advantage of providing a common framework to the wave calculation and to the quasilinear response description. Two important points are discussed: firstly, we show that the irreversible part of the power transferred from the wave to the plasma particles is directly available and does not require an explicit evaluation of the kinetic flux; secondly, it is demonstrated that the symmetry of the obtained plasma functional ensures that these energy transfers are described in a consistent fashion, regardless of the level of approximation employed to evaluate the particle Hamiltonian. Finally, quasi-local, finite Larmor radius expressions are derived in the framework of this formalism and implemented in a new multi-dimensional full-wave code, named EVE, which is employed to analyse two ICRF heating scenarios for ITER.