On the possibility of low-threshold anomalous absorption in tokamak 2nd-harmonic electron cyclotron resonance heating experiments
Ioffe Physical Technical Institute of RAS - Polytekhnicheskaya st. 26, 194021 St. Petersburg, Russia
Received: 5 March 2012
Accepted: 4 June 2012
The parametric decay of an extraordinary electron cyclotron pump wave to electron Bernstein (EB) wave and ion Bernstein wave leading to anomalous absorption in 2nd-harmonic electron cyclotron resonance heating (ECRH) experiments is analyzed. It is shown that in an axisymmetric system, like tokamak, excitation of the low-threshold absolute parametric decay instability (PDI) is possible in the case of non-monotonic behaviour of plasma density in radial direction and due to poloidal magnetic-field inhomogeneity. The threshold of the absolute PDI instability determined by linear dissipation of the EB wave is shown to be substantially exceeded in nowadays 2nd-harmonic ECRH experiments in tokamaks that provide an explanation for the mysterious ion acceleration effect observed there.
PACS: 52.35.Hr – Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid) / 52.35.Mw – Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.) / 52.35.Qz – Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
© EPLA, 2012