1. Department of Mechanical and Aerospace Engineering, University of California, Davis, California 95616, USA
2. Department of Applied Science, University of California, Davis, California 95616, USA
3. Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA
4. General Atomics, San Diego, California 92121, USA
5. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA