1. Francis Bitter Magnet Laboratory, Plasma Science and Fusion Center, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, Massachusetts 02139, USA
2. Wentworth Institute of Technology, 550 Huntington Ave, Boston, Massachusetts 02115, USA
3. National High Magnetic Field Laboratory, Florida State University, Tallahassee, 2031 Paul Dirac Drive, Florida 32310, USA