Deep Pellet Fueling And Its Effect On Tritium Burn-up Fraction In CFETR Plasma

One of key missions of CFETR(Chinese Fusion Engineering Testing Reactor)is to achieve tritium self-sufficiency,for which purpose the tritium burn-up fraction should be greater than 3%,with approximately 1 GW output fusion power.In this work,the STEP integrated modeling workflow is applied to evaluate the required pellet fueling parameters to achieve the two goals.It's required that the pellet ablation rate and the particle deposition profile is accurately evaluated based on proper pellet ablation and deposition models.In this work,the pellet ablation rate is calculated based on a scaling formula from the latest ablation model developed by Parks,and the magnetic field effect on pellet ablation rate is included to improve the formula.It's predicted that the pellet ablation rate is reduced strongly by the strong magnetic field in CFETR,and thus the pellet penetration is deeper.An areal deposition model is developed to resolve the tangential singularity confronted by the widely used point deposition model,and it's generalized to calculate the deposition density with arbitrary injection angle,which makes it suitable for calculating the pellet deposition profile with arbitrary injection geometry.A 0.5D reduced model is developed to consider the drift of the ablation cloud crossing the magnetic field based on the 1D Pressure Relaxation Lagrangian model developed by Parks.The predicted pellet deposition profiles agree well with D?-D experimental data.By scanning the pellet injection position on CFETR,it's found that high field side(HFS)midplane injection is the most advantageous to achieve deep fueling.The areal deposition model and the 0.5D reduced drift model is applied to the pellet ablation/deposition code PAM,which is incorporated into the integrated modeling workflow to provide the particle source information from pellets for the transport module.The STEP workflow is used to evaluate the required pellet fueling parameters to achieve 1 GW fusion power and 3%tritium burn-up fraction in CFETR plasma.It's predicted that a velocity of 850 m/s is required,if a 1:1 homogeneous DT pellet with 100 ?m carbon shell is injected from HFS midplane.Such a velocity is expected to be achieved relatively easily,considering the strength of the pellet is enhanced by the carbon shell.Lower velocity is expected to be enough if a 'sandwich'pellet with tritium inside,deuterium outside,encapsulated with beryllium or carbon shell is adopted.The simulation results from the integrated modeling indicate that the optimized fueling scheme is to inject the 'sandwich' pellets from HFS midplane with a velocity as high as possible.This work is especially meaningful and important to provide a guidance for the design of pellet fueling system in future fusion reactors like CFETR from tritium burn-up fraction point of view.