Use of the Culham He model He II atomic data in JET EDGE2D-EIRENE simulations

Present-day large plasma machines use a divertor containing a cold, dense plasma to act as a buffer between the hot core and the plasma-facing material surfaces, providing protection for the latter. The behaviour of the divertor plasma, including the power radiated by fuel and impurity species, is therefore crucial in determining the performance of the next-step machines such as ITER, requiring transport modelling of the plasma edge and divertor. Transport codes that simulate the edge and divertor plasmas rely on the availability of accurate atomic and molecular data both for the fuel and impurity species. It is important to understand the sensitivity of the simulations to these data, since this determines the quality of the atomic and molecular data required. Recent work has led to the generation of the CHEM (Culham He Model) atomic dataset for hydrogenic He II (He+) [1], [2]. The sensitivity of the simulation codes to the atomic data is being tested by comparing their use in EDGE2D-EIRENE simulations with the presently used data from the ADAS database [3]. Helium is widely used in laboratory fusion experiments both as a fuel as in the first, non-nuclear phase of ITER, as a minority gas for RF heating and will occur as ash from the thermonuclear reactions. The atomic physics of He II is in many ways similar to that of D I, so this study will inform work on D fuelled simulations. He rather than D is considered first, since the former presents a more tractable atomic physics problem in that the heavy particle collisions [1] involve ions rather than neutrals. The use of He simulations also avoids the complications that can result from molecular emissions, allowing easier comparisons with experiment. However, it should be noted that the present simulation results are not compared with measurements in this paper.