1. Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, China
2. ENEA, Fusion and Nuclear Safety Department, C. R. Frascati, Via E. Fermi 45, 00044 Frascati (Roma), Italy
3. Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany