1. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540, USA
2. Electrical and Computer Engineering Department, Colorado State University, Fort Collins, Colorado 80523, USA
3. Physics Department, Colorado State University, Fort Collins, Colorado 80523, USA
4. Department of Physics, University of Nevada, Reno, Nevada 89557, USA
5. Lawrence Livermore National Laboratory, Livermore, California 94550, USA