Perturbative particle transport studies in the W7-AS stellarator

Electron transport coefficients have been determined in the W7-AS stellarator. The diffusion and convection coefficients were obtained by modulating the gas feed into the plasma and by measuring the propagation of the density perturbation. The experiments were carried out at a variety of plasma densities, heating powers and magnetic fields. The results are summarized in the form of a scaling expression for the diffusion coefficient. Transient inward convection was found in the boundary plasma. This convection plays a minor role in the core plasma except with higher heating power, where outward convection was observed. The results are compared with earlier W7-AS transport results.