Investigation on impurity transport using LBO technique

1. IntroductionIt is a common phenomenon in the tokamak devices that impurities have a concentrated trend towards the plasma central region. Impurity sourcesand its transport are very complicated, traditionalpassive methods can not be satisfied for the investigation of impurity transport. So transient perturbation methods have been developed and recognizedas the most appropriate for impurity transport measurement.The LBO technique is just the right transient perturbation method for this task…

Investigation .on impurity transport using LBO technique

Impurity transport has been investigated on the HL-1M tokamak under the con ditions of the ohmically heated discharge (OHD) and the lower hybrid current drive (LHCD). A small quantity of metallic impurity A1 were injected into the plasma using the laser blow-off (LBO) technique. The ionized metallic impurity lines were measured using a vacuum ultra-violet (VUV) spectrometry. Al impurity transports in the plasma under the conditions of the OHD and LHCD were analyzed. The diffusion coefficient (D(r)) and inward convection velocity (V(r)) were ob tained using numerical simulation with the impurity transport code (ITC). The simulation results showed that the transport coefficient during the LHCD decreased by fifty per cent compared with that during the OHD. Therefore the impurity-confined characteristics of the LHCD plasma was obviously improved.