Direct fuelling of the core region of a tokamak by compact torus (CT) injection plays a crucial role for fuelling and burning efficiency in a fusion reactor. However, the penetration and deposition processes of CT in fusion devices involve complex physical mechanisms. The objective of this study is to investigate the dynamic behavior of CT in a tokamak and assess the impact of fuel particle deposition on the bulk plasma parameters profiles, based on fundamental physical mechanisms and actual injection scenarios. This article reports a study which, for the first time, investigates (a) the penetration of a CT in a tokamak with the realistic peaked temperature and density profiles, (b) the influence of magnetic tension force on the CT trajectory and penetration parameters is evaluated, and (c) the effect of CT particle deposition on the tokamak density profile assuming that CT deposits its particles at a constant time rate without changing other CT parameters. A new dynamic model is proposed here to describe the penetration mechanism of CT in fusion devices. This model combines elements of the conducting sphere (CS) model and the nonslipping sphere (NS) model, while also accounting for realistic injection scenarios. The simulations use the HL-3 tokamak configuration as an example, assuming tangential CT injection on the mid-plane. By comparing the CT penetration depth estimated from the new dynamic model with that from the original model, a radial penetration difference of 0.23 m is observed, which corresponds to 35% of the HL-3 tokamak’ s small radius of 0.65 m. Furthermore, the effect of the profiles of the tokamak plasma parameters and CT fuel particle deposition is discussed. The reduced MHD drag force in the outer region with lower temperature and density facilitates CT penetration, while the loss of CT particles and thus the directional CT momentum along the injection direction hinders CT penetration. In a particular set of assumptions, CT penetration depth decreases by 31% when considering the deposition of CT particles compared to the case when the particle deposition is not considered. Finally, the analyses and simulations reveal that CT injection preferentially modifies tokamak density profile at the deepest CT penetration location in the central region.
This paper investigates how injecting a compact torus (CT) of fuel into a tokamak affects the plasma density profile. It proposes a new model to simulate CT penetration and shows that CT deposition can significantly impact the density profile, especially in the central region.