Simulation of lithium transport using the BOUT++ framework

A numerical model that calculates the collisional interactions between the lithium atoms from a lithium pellet and the background plasmas has been upgraded. The ion density (N_i), electron temperature (T_e), ion temperature (T_i) and parallel ion velocity (V_∥,i) are used to characterize the background plasmas. The lithium atom density (N_Li^a) and parallel velocity (V_∥,a) of lithium atoms evolve with time. For each lithium ion, the density (N_Liⁿ⁺), temperature (T_Liⁿ⁺) and parallel velocity (V_∥,Liⁿ⁺) are self-consistently calculated. A C-mod lower single null equilibrium is used to generate the grid for the BOUT++ simulation. The lithium atoms can be fully ionized to Li³⁺ in ∼2 μs. The rapid radial and poloidal expansion of the lithium ions are found in the simulation. After the collision interaction process, the electron temperature rapidly decreases at the pellet location; then, it rapidly poloidally expands, and the temperature at the pellet location starts to recover. The electron pressure increases at the pellet location despite the decrease in electron temperature because of the extra electrons from the lithium ionization. The ion pressure profile decreases in the pellet location due to the decrease in ion temperature.