1. Institute for Plasma Research 1 , Bhat, Gandhinagar 382428, India
2. Department of Physics, School of Physical Sciences, Sikkim University 2 , Gangtok, Sikkim 737102, India
3. Princeton Plasma Physics Laboratory 3 , Princeton, New Jersey 08536, USA
4. Department of Physics 4 , S.V.N.I.T. Surat, Surat 395007, India
5. Naval Research Laboratory 5 , Washington, DC 20375, USA