All the main features of the scrape-off layer turbulence, magnitude, frequency spectrum and perpendicular wave vector, ξt, are strongly affected by the injection of lower hybrid (LH) power into the FTU tokamak. The governing parameters are the local last closed magnetic surface values of density, ne,LCMS, and temperature, Te,LCMS. ne,LCMS determines the perpendicular wave vector of the LH waves, which is a key parameter for the multiple scattering processes, and together with Te,LCMS the collisionality that exerts a stabilizing effect on the fluctuations. This effect, still to be examined in the light of theoretical models, leads to an asymptotic value for the fluctuation relative amplitude in the ohmic phase close to 25%, and ∼10% in the LH phase, or even less, since the saturation level is not yet attained. The LH waves also can strongly raise ξt, about 3 times, and double the root mean square frequency. The transfer of momentum and energy in the mutual scattering of LH and turbulence 'waves' drives these changes. An increase also of the cross-correlation between temperature and electric potential fluctuations should occur in order to explain the magnitude of the fluctuation amplitude drop and the large increment of the temperature e-folding decay, by more than a factor of 2.5. Particle transport, however, does not appear to be affected to a large extent—the density e-folding decay length is almost unchanged but the power flow typical length rises by about a factor of 1.5, which is a relevant figure in view of the problem of mitigating the power loads on divertor targets in future reactors. These changes are confined mainly within the flux tube connected with the LH waves launching antenna, but start to spread significantly out of it at high plasma densities.
Wave penetration and power deposition of helicon current drive for magnetic fusion plasma with sharp edge gradient