Different Techniques for Investigation of Plasma Diffusion Coefficient in IR-T1 Tokamak

摘要

Diffusion due to the run-away electrons in Tokamak can cause serious damages to the Tokamak walls. In this study, aiming for improving the plasma confinement, the diffusion coefficient was calculated in two different approaches using two different probes. In the first approach; Langmuir probe, was utilized to measure the poloidal electric field, radial flux and consequently the diffusion coefficient. On a more approach, the diffusion coefficient has been estimated by using the ball-pen probe and the Fourier-transform and the assumption of entirely diffusive plasma penetration inside the boron nitride shielding. In order to improve the plasma confinement, external biased voltages of ± 200 V were applied when the plasma experienced its stable phase. Comparing the results, a clear unity can be seen from both the Langmuir approach and the Ball-pen approach. As the results indicate, the diffusion coefficient in Langmuir approach decreased up to 40% when the positive biased voltage of 200 V was applied. However, when the negative biased voltage of 200 V was applied, the diffusion coefficient increased significantly (up to 60%). Ball-pen approach results signify the same results from Langmuir probe. Where, by applying the positive biased voltage of 200 V the diffusion coefficient decreased by almost 40% and on the contrary, the negative biased voltage of 200 V increased the diffusion coefficient up to 30% in general. It can be said that the positive biased voltage contributed to improve the plasma confinement in Tokamak.