Time-and-space resolved comparison of plasma expansion velocities in high-power diodes with velvet cathodes

Journal Article · Mon Jan 28 00:00:00 EST 2013 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4789623· OSTI ID:22102236

Jie, Yang; Ting, Shu; Yuwei, Fan ^[1]

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1. College of Opto-electric Science and Engineering, National University of Defense Technology, Hunan 410073 (China)

Time-and-space resolved comparison of the expansion velocities of plasmas in the planar diode with cathodes made of carbon velvet and polymer velvet has been performed. The diode was powered by a 200 kV, 110 ns pulse, and the peak current density was nearly 477 A/cm{sup 2}. A four-channel high speed framing camera (HSFC) was used to observe the formation and subsequent movement of the cathode plasmas. More accurate and valuable information about the two-dimensional (radial and axial) velocity components of the cathode plasmas was also acquired by utilizing the digital image processing methods. Additionally, the perveance model based on the Child-Langmuir law was used to calculate the expansion velocities of the diode plasmas from voltage and current profiles. Results from the two diagnostics were compared. Comparing the average values of the radial and axial velocity components indicated that the former was much larger than the latter during the initial period of the current. It was also found that the radial velocity of the carbon velvet cathode (190 cm/{mu}s) was much larger than that (90 cm/{mu}s) of the polymer velvet cathode. Moreover, the average values of both the radial and axial velocity components of the carbon velvet cathode were typically in the range of 2.5 {+-} 1.5 cm/{mu}s, which were smaller than that of the polymer velvet cathode during the current flattop. These results, together with the comparison of calculated values from the perveance model, indicated that the diode with carbon velvet cathode was more robust as compared with the polymer velvet cathode for the same electron current densities.

• OSTI ID: 22102236
• Journal Information: Journal of Applied Physics, Vol. 113, Issue 4; Other Information: (c) 2013 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON
CATHODES
COMPARATIVE EVALUATIONS
CURRENT DENSITY
ELECTRIC CURRENTS
ELECTRIC POTENTIAL
IMAGE PROCESSING
PLASMA
PLASMA DIAGNOSTICS
PLASMA EXPANSION
POLYMERS
PULSES
RADIAL VELOCITY
THERMIONIC DIODES
TWO-DIMENSIONAL CALCULATIONS