Measurement of the local carbon diffusion coefficient in the S-l spheromak

Abstract

The local carbon diffusion coefficient has been measured in the S-l spheromak by detecting the radial spread of injected carbon impurity. The radial impurity density profile is determined by the balance of ionization and diffusion. Using the measured local electron temperature and density, the ionization rate is determined from which the particle diffusion coefficient is inferred. The results found in this work are consistent with Bohm diffusion, and the absolute magnitude of the local particle transport coefficient D⊥ is found to be (4-6) × DBohm. The measured particle transport rates are correlated with the plasma pressure gradients, suggesting a pressure driven transport mechanism.