Lower hybrid wave scattering and turbulent electron heating at the WIIA-stellarator

The propagation of Lower Hybrid Waves in the presence of large amplitude drift wave fluctuations has been investigated in a 1 = 2 stellarator (B <= 0.3 T, nsub(e) <= 5.1017 m-3, deltansub(e)/nsub(e) <= 0.6). Severe decorrelation of the wave as well as considerable broadening of the perpendicular wavenumber spectrum with a nearly isotropic distribution is found. Strong damping of the LH-wave is observed, which cannot be attributed to collisions or electron Landau damping. High power LH-waves are shown to heat the electrons efficiently. The energy transfer from the turbulent LH-spectrum to the electrons is accounted for by an effective collision frequency νsub(e)sup(eff) (k perpendicular to) = D perpendicular to sup(t) k perpendicular to 2. An electron energy balance demonstrates that turbulent heating is by far dominant. Reasonable agreement between the observed heating and the power transfer from the turbulent spectrum is obtained if D perpendicular to sup(t) is estimated from the properties of the drift wave spectra. (author)