1. Institute of Physics, University of São Paulo, São Paulo, SP 05508-090, Brazil
2. Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08543, USA
3. Institute for Fusion Studies, University of Texas, Austin, Texas 78712, USA
4. University of California, Irvine, California 92697, USA
5. General Atomics, San Diego, California 92186, USA