Analysis and Modelling of the Relationship Between WI, and WII Emission Signals and Tungsten Net Erosion in the DIII-D Divertor

Accurate estimation of net tungsten (W) sources remains difficult but essential for control and reactor design. Using the Local Particle Transport Model for eroded materials (LPTMC), we show that under reactor-relevant plasma-wall conditions, WII emission cannot directly represent the net W source. LPTMC simulations suggest that for the DIII-D lower divertor plasma conditions, the assumption that WII radiation originates mainly from non-redeposited W gradually breaks down as divertor plasma pressure increases. Conversely, assuming WII emission arises from redeposited W holds for high plasma pressures ( Pa) compared to typical DIII-D values ( Pa). For DIII-D, WII signals mix redeposited and non-redeposited contributions, requiring modeling to interpret the measurement. LPTMC simulation results indicate that if W sputtering is induced by ions with average impact energy greater than 350 eV, net W sources might be expressed as a function of WI emission. In this regime, LPTMC simulation results can be reduced to a fit linking WI emission to net W erosion, without the need to make assumptions about the plasma impurity content. Understanding W net sources is critical, as W's low core tolerance risks plasma collapse.



Acknowledgements: Work supported by US DOE under DE-FC02-04ER54698 and DE-SC0015877