Experimental evidence of three-wave coupling on plasma turbulence

Experimental evidence of the nonlinear nature of the broadband edge fluctuations has been obtained in edge turbulence in the Advanced Toroidal Facility torsatron. Whereas little nonlinear wave interaction is found in the scrape-off layer region, three-wave coupling is enhanced in the plasma edge region ([ital r][lt][ital a][sub shear]). The degree of three-wave coupling strongly depends on the plasma conditions; it decreases in the temperature range ([ital T][sub [ital e]][approx]10 eV) where the ionization rates depend strongly on [ital T][sub [ital e]] suggesting a link between ionization source and turbulence.