1. Plasma Science and Fusion Center, and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
2. Física de Materiais, Escola Politécnica de Pernambuco, UPE, Recife, Pernambuco 50720-001, Brasil
3. U.S. Army CCDC Army Research Laboratory, Adelphi, Maryland 20783, USA
4. Department of Physics, Northeastern University, Boston, Massachusetts 202115, USA
5. Materials Research Laboratory, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
6. Department of Electrical Engineering, California Institute of Technology, Pasadena, California 91125, USA
7. Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA