Impurity Transport Studies using TESPEL in W7-X stellarator

The TESPEL injection system has been successfully commissioned on the W7-X stellarator. The local deposition of the tracer impurities of the TESPEL has been confirmed at the various W7-X plasmas. Depositing the impurities in the core plasma of W7-X by means of the TESPEL offers a unique opportunity to study the impurity transport in the core plasma. The comparison between LBO (impurity source at the edge) and TESPEL (impurity source in the core) allows us to obtain an enhanced view on profiles of impurity transport coefficients, diffusivity and convection velocity. Taking advantage of the unique feature of the TESPEL, the impurity transport in the core plasma of W7-X in different configurations has been studied with the TESPEL. The experimental results suggest that the W7-X plasma with the standard configuration seems to have a longer impurity confinement than that with the high mirror and high iota configurations. In order to draw an accurate conclusion, a one-dimensional modelling with the STRAHL code for estimating impurity transport coefficients is highly important and it will be a next step.