Hamiltonian theory of the ion cyclotron minority heating dynamics in tokamak plasmas
The question of heating a tokamak plasma by means of electromagnetic waves in the Ion Cyclotron Range of Frequency (ICRF) is considered in the perspective of large RF powers and in the low collisionality regime. In such cases the Quasi Linear Theory (QLT) is validated by the Hamiltonian dynamics of the wave particle interaction which exceeds the threshold of the intrinsic stochasticity. The Hamiltonian dynamics are represented by the evolution of a set of three canonical action angle variables well adapted to the tokamak magnetic configuration. This approach allows the RF diffusion coefficient to be derived with very few assumptions. The distribution function of the resonant ions is written as a Fokker Planck equation but the emphasis is put on the QL diffusion instead of on the usual diffusion induced by collisions. Then the Fokker Planck equation is given a variational form from which a solution is derived in the form of a semi analytical trial function of three parameters: the percentage of resonant particle contained in the tail, an isotropic and an anisotropic width. This solution is successfully tested against real experimental observations. Practically it is shown that in the case of JET the distribution function is influenced by adiabatic barriers which in turn limit the Hamiltonian stochasticity domain within energy values typically in the MeV range. Consequently and for a given ICRF power, the tail energy excursion is lower and its concentration higher than that of a bounce averaged prediction. This may actually be an advantage for machines like JET considering the energy range required to simulate the alpha-particle behaviour in a relevant fusion reactor.
Bibliographic Reference: Report: EUR-CEA-FC-1391 EN (1990) 52 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199011073 / Last updated on: 1994-12-01
Original language: en
Available languages: en