STRAHL modeling of impurity transport on Wendelstein 7-X during the first divertor campaign*

In the first divertor operational phase (OP 1.2a) of Wendelstein 7-X, impurity transport experiments were performed with iron via laser blow-off injection. The x-ray imaging spectrometer systems, HR-XIS and XICS, were used to measure the He-like spectra at various input ECRH heating powers and plasma densities. These measured He-like iron spatial and temporal emissivities can then be used to estimate the He-like iron’s diffusion and convective velocity parameters. Utilizing the 1D transport code STRAHL, the spatial and temporal evolution of the He-like iron charge state is modeled for assumed stationary anomalous diffusion and convective velocity profiles. To match both the observed total He-like iron emissivity and a corresponding spatially inverted emissivity profile, a chi-squared minimization is done on the experimental data by varying the input spatial values of the anomalous diffusion and convective velocity parameters in STRAHL.