The Ablation Of Pellet In Tokamak Plasma

Nuclear fusion offers human beings a new viable means for producing energy sustainably.Tokamak is a kind of fusion devices which is most feasible and economic to achieve fusion.The injection of deuterium pellets can not only provide fuel for tokamak,but also pace ELMs to mitigate their damage to the plasma-facing-wall.In contrast,injection of low Za impurity pellets can help control plasma discharge and diagnose the plasma.Recently,it has been found that the injection of lithium can be used to ELMs pacing,wall conditioning,current density profile measurement and fast plasma termination.However,these applications depend on detailed parameters of injection such as pellet radius and speed Therefore,it is important to study the ablation of Lithium pellets to evaluate physical quantities like released impurity density,penetration,etc.This dissertation focuses on the ablation of lithium pellet in tokamak plasma using Park's one-dimensional spherically symmetric,neutral gas shielding model.In the model,quasi-steady conditions are assumed.With the model,the distributions of temperature,flow velocity,pressure,and energy flux and mean energy of electrons in the ablation cloud are obtained.These results are compared with those of the ablation of hydrogen and boron pellets.The principal difference between hydrogen and low Za pellet ablations results from the enormous discrepancy between their sublimation energies.It is also found that the ability of ablation cloud to shield electron energy flux differs between different material pellets.The pellet with a higher sublimation energy has a stronger ability to shield the electron energy flux.The shielding ability of any pellet varies in the ablation cloud,the inner region has a stronger shielding ability.The shielding ability depends on the density of the ablation cloud.The work of thesis has laid the foundation for future study on the ablation of Lithium pellet in the edge plasma.