1. Institute for Fusion Studies, University of Texas at Austin 1 , Austin, Texas 78712, USA
2. Physics, Faculty of Science, Ain Shams University 2 , Cairo 11566, Egypt
3. Oak Ridge National Laboratory 3 , Tennessee 37830, USA
4. Princeton Plasma Physics Lab, Princeton University 4 , Princeton, New Jersey 08540, USA
5. Center for Integrated Plasma Studies, University of Colorado Boulder 5 , Colorado 80309, USA