Quasi-linear evolution of electron cyclotron absorption by an RF-generated extended tail in tokamak plasmas

Quasi-linear theory is employed to study the time evolution of the absorption coefficient for extraordinary mode electron cyclotron waves by an extended electron tail in momentum space, in a magnetized plasma under the action of externally launched lower hybrid and electron cyclotron waves. Lower hybrid waves are used to generate the extended tail and electron cyclotron waves interacting with the tail electrons are introduced. The results show that the absorption coefficient for the central ray of the spectrum of cyclotron waves increases with the width of the spectrum and it is shown that the asymptotic absorption coefficient may be larger than the value at the onset of electron cyclotron waves, for sufficiently large angle of injection relative to the normal to the magnetic field. (Author)