1. Blackett Laboratory, Imperial College, London SW7 2BW, United Kingdom
2. Sandia National Laboratories, PO Box 5800, Albuquerque, New Mexico 87185-1193, USA
3. Department of Physics, University of Alberta, Edmonton, Alberta T6G 2J1, Canada
4. Key Laboratory of Pulsed Power, Institute of Fluid Physics, CAE, Mianyang 621900, China