1. Plasma Sources and Applications Centre/Space Propulsion Centre; NIE; Nanyang Technological University; Singapore 637616 Singapore
2. School of Chemistry; Physics and Mechanical Engineering; Queensland University of Technology; Brisbane QLD 4000 Australia
3. CNRS; ICARE; Electric Propulsion Team; 1c Avenue de la Recherche Scientifique 45071 Orléans France
4. Mechanical and Aerospace Engineering; George Washington University; Washington DC 20052 USA