Spectroscopic studies of fuel recycling and impurity behaviors in the divertor region of Wendelstein 7-X

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom Research and Training Programme 2014–2018 under Grant Agreement No. 633053. The authors are thankful for the support from the China Scholarship Council. This work is also supported by National Natural Science Foundation of China (No. 11675050).