Impurity Transport Study with TESPEL Injection and Simulation

Abstract

Impurity behaviors in LHD are studied by a Tracer-encapsulated Solid Pellet (TESPEL) injection. By containing multiple tracers in a TESPEL, the different tracer species have been compared simultaneously under the same plasma condition. The density disturbance on the bulk plasma by TESPEL is typically less than 10 %. The amount of the tracer particles deposited locally inside a plasma is about a few 1017 particles which is smaller than that of the bulk plasma by a factor of three orders of magnitude. Triple tracers, V, Mn and Co are used, because the charges of nuclei of intrinsic impurities, Cr and Fe are in between those of the tracers. The impurity confinement behavior depends substantially on the electron density. In case of the density higher than ne = 5×1019 m−3, the tracer impurity in the plasma core was kept for a long time, while it decays in order of 500 ms in the medium density case. Such temporal behavior is compared with a STRAHL simulation code assuming diffusion coefficient and convection. The general behavior fits well with the emissivity value integrated along the sight line.