Temperature fluctuations and turbulent transport at the edge of the SINP tokamak

Abstract

Density, temperature and potential fluctuations have been measured in the edge region and the scrape off layer (SOL) of the SINP tokamak. The triple probe technique has been used to obtain the instantaneous value of these quantities simultaneously and virtually at the same spatial position. The fluctuation levels thus found are significant (T̃e/Te≈20–35% and ñ/n≈35–55%) and the spectra are broadband. The effect of temperature fluctuation on the turbulent transport has also been investigated and found to be considerable. The measured diffusion coefficient comes out to be about twice the Bohm diffusion coefficient. Radial profiles show sharp density and temperature gradients and there exists a self-generated Er×B velocity shear layer near the limiter. The results have been compared with the existing theories of edge turbulence in tokamaks and the rippling mode driven by the resistivity gradient has been identified as the most probable mechanism.