Spectroscopic investigation of the tungsten deuteride sputtering in the EAST divertor

Abstract

• Behaviors of WD molecules sputtering were compared with W atoms sputtering in EAST. • Existence of energy threshold for WD sputtering in EAST was discussed. • Influences of heat flux and D retention on WD sputtering in EAST were analyzed in detail. Physical sputtering caused by particle bombardment is believed to be the main erosion mechanism of W materials in fusion devices, in which W atoms are the sputtering products. However, the tungsten deuteride molecule (WD) spectra have been observed in both TEXTOR and ASDEX Upgrade, which was believed to be the product of chemically assisted physical sputtering (CAPS), a new sputtering mechanism that has been proposed in recent years. In this paper, we report the spectroscopic observation of WD molecules in the EAST W divertor. The behaviors of WD molecules sputtering are compared with W atoms sputtering via the spectral measurements of the ro-vibrational band emission of WD 6 Π → 6 Σ + in the spectral range between 673 nm and 678 nm and the WI line emission at 400.9 nm. The physical sputtering characters and chemical sputtering characters of WD molecule sputtering were confirmed in EAST. The measurements in EAST showed that there is an energy threshold for WD molecules sputtering and that the sputtering energy threshold of WD molecules is smaller than that of W atoms. Furthermore, the dependence of WD molecule sputtering efficiency (the absolute WD photon flux ( Ph WD ) normalized to the particle flux ( Γ ion ) reaching the target with a constant T e ) on impact energy and heat flux were studied, presenting significantly different behaviors compared with W atom sputtering. In addition, it is found that the decrease of WD sputtering efficiency with the heat flux is accompanied by the rise of the photon flux of D δ (410.06 nm) normalized to the particle flux ( Γ ion ) at the divertor target, which may imply the enhanced deuterium desorption at the W surface. The further increase of heat flux hitting the target surface could elevate the surface temperature and benefit the deuterium release from the surface, which may influence the formation of WD molecules at the surface layer.