Plasma rotation effect on interaction of low frequency fields with plasmas at the rational surfaces in tokamaks

Abstract

The effect of plasma rotation on low frequency (LF) field penetration, absorption and ponderomotive forces in TEXTOR and in Tokamak Chauffage Alfvén Brésilien (TCABR) is investigated in the frequency band of 1–10 kHz. The LF fields are driven by the dynamic ergodic divertor in TEXTOR and the ergodic magnetic limiter in TCABR. Alfvén wave mode conversion is responsible for the LF field absorption at the rational magnetic surface where q = −M/N is the integer. Analytical and numerical calculations show the maxima of the LF field absorption at the local Alfvén wave resonance |ω − k · U| = |k∥| cA, where ω and k are the frequency and the wave vector, respectively, and cA is the Alfvén velocity at the rational magnetic surface q = 2, 3 in TEXTOR and TCABR. The rotation velocity U along the magnetic surfaces, taken into account in the dielectric tensor, can strongly modify the LF field and dissipated power profiles. The absorption in the local AW resonances begins to be non-symmetric in relation to the resonance surface. Calculations show that coil impedance has a maximum related to excitation of some stable (possibly Suydam) modes for waves travelling in the direction of plasma rotation.