Study of the evolution of density and particle transport during density relaxation phase after pellet fueling on the EAST tokamak

Abstract

The impact of pellet injection depth on particle transport characteristics and density profile evolution during the post-pellet density relaxation phase is investigated on the Experimental Advanced Superconducting Tokamak (EAST). Experiments were conducted under similar background plasma conditions and the results showed that variations in pellet deposition depths led to differences in density profiles despite comparable core fueling efficiencies. By computing the effective particle transport coefficients immediately after the pellet injection, it is found that the differences in density profiles are mainly due to significantly different transport velocities in the inner region of ρ < 0.4. The potential influence of pellets on electrostatic turbulence in this region is investigated using the Trapped Gyro Landau Fluid (TGLF) model and CO2 laser collective scattering diagnostics. The simulation suggests that the increase in transport coefficients following pellet injection is attributed to the destabilization of lower-k modes rather than the higher-k modes within the diagnostic measurement range.