Features of space-charge-limited emission in foil-less diodes

Journal Article · Mon Dec 15 04:00:00 EST 2014 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4903205· OSTI ID:22407943

Wu, Ping; Yuan, Keliang; Liu, Guozhi ^[1]; Sun, Jun ^[2]

---

1. Department of Engineering Physics, Tsinghua University, Beijing 100084 (China)
2. Science and Technology on High Power Microwave Laboratory, Northwest Institute of Nuclear Technology, Xi'an 710024 (China)

Space-charge-limited (SCL) current can always be obtained from the blade surface of annular cathodes in foil-less diodes which are widely used in O-type relativistic high power microwave generators. However, there is little theoretical analysis regarding it due to the mathematical complexity, and almost all formulas about the SCL current in foil-less diodes are based on numerical simulation results. This paper performs an initial trial in calculation of the SCL current from annular cathodes theoretically under the ultra-relativistic assumption and the condition of infinitely large guiding magnetic field. The numerical calculation based on the theoretical research is coherent with the particle-in-cell (PIC) simulation result to some extent under a diode voltage of 850 kV. Despite that the theoretical research gives a much larger current than the PIC simulation (41.3 kA for the former and 9.7 kA for the latter), which is induced by the ultra-relativistic assumption in the theoretical research, they both show the basic characteristic of emission from annular cathodes in foil-less diodes, i.e., the emission enhancement at the cathode blade edges, especially at the outer edge. This characteristic is confirmed to some extent in our experimental research of cathode plasma photographing under the same diode voltage and a guiding magnetic field of 4 T.

• OSTI ID: 22407943
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 21; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
CATHODES
COMPUTERIZED SIMULATION
CURRENTS
ELECTRIC POTENTIAL
MAGNETIC FIELDS
MICROWAVE RADIATION
PHOTOGRAPHY
PLASMA
RELATIVISTIC RANGE
SPACE CHARGE