1. ENEA C. R. Frascati, Via E. Fermi 45, C.P. 65-00044 Frascati, Rome, Italy
2. Max-Planck-Institut für Plasmaphysik, Boltzmannstraße 2, D-85748 Garching, Germany
3. Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027, People's Republic of China