An experimental study of the harmonics generated during Alfven wave heating at TCA

Abstract

During plasma excitation by high power Alfven waves at TCA, signals at harmonics of the generator frequency are observed in the plasma scrape-off layer. Experimental investigations of the sheath effect and the excitation efficiency and dispersion properties of the harmonics are reported. The results indicate that the harmonics arise, either directly or indirectly, through the driven Alfven waves and not through the sheath effect at the exciting antenna. The RF ion saturation current is observed to have a nonnegligible peak amplitude in comparison with the time averaged ion saturation current and may provide evidence of a nonlinear evolution of the driven Alfven waves

Calculations of wave excitation and dissipation in Tokamak Chauffage Alfvén wave heating experiment in Brazil

“…1 In tokamaks, a rather comprehensive study of Alfvén wave absorption and heating was carried out at Lausanne in the Tokamak Chauffage Alfvén ͑TCA͒ device. 4,5 The mode spectrum of Global Alfvén Waves ͑GAW͒ excited by long wavelength antennae, which produce toroidal wave numbers NϭϮ1 to Ϯ4 and poloidal wave numbers M ϭϮ1, was thoroughly characterized. The peaks observed in the antenna impedance, which is a measure of the antenna-plasma coupling, agree well with the results of numerical simulations, although the magnitude of the coupled power is much smaller than theoretically predicted.…”

Nonlinear Resonant Absorption of Surface Magnetohydrodynamic Waves

“…However, Alfven wave heating experiments have been performed which indicate that the driven Alfven waves may undergo a nonlinear evolution [5]. This is not surprising, considering the field amplification that takes place at the resonance surface, where the local Alfven wave frequency matches the surface wave frequency.…”

“…For notational convenience we have dropped the superscript (1) on all the amplitudes in Eqs. (5) and (6). When deducing Eqs.…”

“…When deducing Eqs. (5) and (6) we have assumed the linear scalings (and the lowest order perturbation expansion for W(2), xIt(pl, etc. ) to be valid as order of magnitude estimates [8], i.e.…”

“…(6) but not in Eq. (5) is that the magnitude of the ratio of nonlinear and linear terms in Eq. (5) are of higher order in a kAx expansion compared to that in Eq.…”