Full-torus impurity transport simulation in boron powder injection experiments in the Large Helical Device

• The installation position of an Impurity Powder Dropper was optimized by simulation. • Simulation reproduced the ablation positions of dropped boron powders in the plasma. • Boron emission was detected near a divertor plate at a visible spectrometer array. • The peak of intensity profiles of boron emission decreased with the plasma density. • Toroidal uniformity of boron deposition can deteriorate in higher-density plasmas. The toroidal distribution of boron deposition on plasma-facing components (PFCs) in boron powder injection using an impurity power dropper (IPD) was investigated by full-torus simulation and observations in a systematic plasma density-scan experiment. The images of the ablation of dropped boron powders observed with a visible CCD camera were consistently explained by the simulations of the ablation positions of the boron powders considering the size distribution. Simulations assuming full-torus boron deposition on the PFCs did not reproduce the observed intensity profile of boron emission lines for higher plasma densities. It indicated that the density of boron deposited on PFCs installed toroidally far from the IPD was low for higher plasma densities due to the change in the ablation positions of the boron powders toward the outboard side. The experimental results verified the previous full-torus simulation of the toroidal distribution of the boron deposition in both lower and higher plasma densities.