Numerical estimate of multi-species ion sound speed of Langmuir probe interpretations in the edge plasmas of Wendelstein 7-X

The recently modified EMC3-EIRENE code package has been widely applied as an edge-plasmaanalysis tool and resulted in successful validation against various measured trends seen instellarator and tokamak plasma boundaries. It has been shown that the code package applied forWendelstein 7-X (W7-X) discharges in the interpretive mode can assess the impact of impurityeffects on the electron density, measured by a set of Langmuir probes. In particular the spatialquantification of impurities and effects from the effective charge state Zeff and effective massmeff, which are non-trivial to record by diagnostics, were examined. The results showed thatearlier assumptions of the effective charge-state distribution and effective mass for reportedLangmuir probe measurements must be revised. Subsequently, reprocessing these measurementswith code-interpreted spatial profiles of the effective charge state and effective mass led to anoverall improved physical consistency.