1. Key Laboratory for Physical Electronics and Devices of the Ministry of Education, Xi'an Jiaotong University, Xi'an 710049, China
2. Beijing Vacuum Electronics Research Institute, Beijing 100016, China
3. National Key Laboratory of Science and Technology on Space Science, China Academy of Space Technology (Xi'an), Xi'an 710000, China
4. Center for Pulsed Power and Power Electronics, Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas 79409, USA