Molecular Dynamics Simulations of Deposition and Damage on Tungsten Plasma-Facing Materials by Tungsten Dust

Classical molecular dynamics has been used to study the interactions between tung- sten （W） plasma-facing materials （PFMs） and dust grains. The impact velocity of dust grains is in the range from 324 m/s to 3240 m/s. The main effect of dust grains with low impact velocity is deposition. However, a material surface can be damaged by high velocity dust grains. The cumulative damage of impacting dust grains has also been take into account. When the impact velocity is low, no significant damage is detected but a porous firm forms on the surface. Serious damage can be produced on PFMs if the impact velocity is high.     

A Molecular Dynamics Study on the Dust-Plasma/Wall Interactions in the EAST Tokamak

The interactions between the W nano-dust and deuterium plasma at different locations of the EAST tokamak are simulated using a molecular dynamics code. It is shown that nano-dust particles, with the radius, R d , ～5 nm, can exist for at least several nano-seconds under the interactions from the ions without being ablated in some specific places of the tokamak edge plasma, while those with R d ≥25 nm may be ablated if the plasma temperature T～ 50 eV and density n～10 19 m 3 . In addition, the collisions of tungsten nano-dust grains with a tungsten wall at 100 m/s or 1000 m/s impinging speeds are simulated. It is demonstrated that the dust will stick to the wall, and the collision will not cause substantial damage to the wall, but it may be able to cause partial destruction of the dust grains themselves depending on their incident speeds.     

PIC-EDDY Simulation of Different Impurities Deposition in Gaps of Carbon Tiles

A 3D Monte Carlo （MC） code PIC- EDDY, based on EDDY （erosion and deposition dynamic simulation） code, was used to investigate the redeposition of different impurities in the gaps of C tiles. By incorporating the rate coefficients of beryllium （Be） and tungsten （W） into the code, we obtain deposition profiles of hydrocarbon, beryllium and tungsten particles in the toroidal and poloidal gaps, respectively. The redeposition rate of tungsten was found to be higher than those of other impurities in the gaps, except at the bottom, due to its easier local deposition within one gyroradius. Due to the effect of reflection coefficients of hydrocarbon fragments on graphite, fewer hydrocarbons were resided at the entrance while more were deposited on the sides of the gap. At elevated plasma temperatures （such as 30 eV）, asymmetric deposition distributions were observed between the toroidal and poloidal gaps due to the dominant ionized particles. Ions were mainly deposited within 1 mm depth inside gaps, and the bottom deposition particles were almost all neutrals.