Estimation of tungsten production from the upper divertor in EAST during edge localized modes*

Abstract

During edge localized modes (ELMs), the sheath evolution in front of the Experimental Advanced Superconducting Tokamak (EAST) upper divertor is studied to estimate the sputtered tungsten (W) atoms from the divertor target. A large potential drop across the sheath is formed during ELMs by compared with inter-ELMs, and the maximum of sheath potential drop can exceed one thousand of eV in current EAST operation. Due to the enhancement of the sheath potential drop during ELMs, the W physical sputtering yield from the deuterium (D) ions and the impurity ions on the upper divertor target is found to be significant. It is established that the sputtered W yield during ELMs is at least higher by an order of magnitude than inter-ELMs, and D ions and carbon (C) ions are the main ions governing the W production for the current H-mode with ELMs discharges. With increase in the pedestal electron temperature, the maximum of the D and C ion impact energy during ELMs shows a nearly linear increase, and the D ions have sufficient impact energy to cause the strong W physical sputtering. As a consequence, the D ions may dominate the sputtered W flux from the divertor target when the C concentration is controlled less than one percent for the higher heating power H-mode with ELM discharges in near future.

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

“…The Monte Carlo simulation by Ou et al also shows similar dependence of the W physical sputtering yield on the bombardment energy and different impurity ions. [19] Thus, it is considered that the Ne seeding decreases the divertor plasma temperature to reduce the impact energy of the incident particles on the one hand, but increases the Ne impurity concentration in the divertor plasma on the other hand. The dependence of W sputtering on T et , as shown in Fig.…”

Study of the tungsten sputtering source suppression by wall conditionings in the EAST tokamak

“…The sputtered C atoms would bombard the W divertor and aggravate the sputtering behavior of W. It is concluded that the low-Z impurities in the D main plasma, such as carbon and beryllium, would cause the sputtering of W divertor plate in the divertor region, rather than pure D incident flow. In the plasma discharge vessel of EAST, the internal parts of carbon-based materials would be bombarded by the edge plasma and generated hydrocarbons, which would influence the W sputtering behavior [29]. It should be noted that the chemical sputtering yield of C usually accounts for only 1% [30], and physical sputtering is mainly considered and discussed, here.…”

Determination of activation energy of ion-implanted deuterium release from W-Y2O3*

“…Tungsten has been considered as one of the candidate PFMs for ITER because of its favorable physical and chemical properties, such as high thermal conductivity, high melting point, high-temperature mechanics performance, low physical and chemical sputtering yields, and no chemical reaction with hydrogen. [1][2][3][4][5][6][7] However, the brittleness of W material leads PFM to likely undergo crack failure when the transient event occurs. [8] W-Y 2 O 3 alloys can effectively impede the recovery and recrystallization at high temperature, and have low ductilebrittle transition temperature (DBTT) compared with pure tungsten.…”