Speaker
Description
The penetration depth of pellets mainly depends on the ablation rate, which further influences fueling efficiency. In this work, based on the neutral gas shielding model [1], we proposed a neutral gas evaporation shielding (NGES) model, in which the ablation cloud radius was evaluated self-consistently to account for the real-time shielding effect of ablated gas on the incoming heat flux. To validate the model, we calibrated it using pellet injection experiments on HL-2A by examining the pellet parameters. The injection velocity, pellet size, and injection location were discussed. Background plasma parameters, including electron density and temperature, were also taken into account.
In the HL-2A tokamak, the core plasma typically operates within a well-defined parameter range. The central electron density generally lies in the range of , while the core electron temperature varies between 0.7 and 1.8 keV. Based on these background plasma conditions, the calculated characteristics of the pellet ablation cloud show a temperature of approximately 2–4 eV and a density of about . We further compared the predicted pellet penetration depth and Hα signals from the model with experimental measurements on HL-2A. These comparisons led to a scaling law under the device conditions. The simulation results show that the ablation rate trends differ from experimental observations by less than 10%, showing the feasibility of the NGES model. Under a wide range of plasma conditions, the ablation model with self-consistent evolution of the ablation cloud radius was compared with the NGPS model. The results exhibit a better agreement with the experimental observations. With further development, the model can be extended to include the rocket effect. The NGES model developed based on HL-2A pellet injection experiments provides a preliminary ground for further investigation of the rocket effect and its impact on fuel pellet trajectories.
[1] Parks P B and Baylor L R Phys Rev Lett 94 1–4