scholarly journals Electric Field Enhancing Artifacts as Precursors for Vacuum High-Voltage Breakdown

Instruments ◽  
2019 ◽  
Vol 3 (4) ◽  
pp. 64
Author(s):  
Rolf Behling

Abrupt formation of plasma in a high-voltage insulating vacuum gap and subsequent discharge of electrodes limits the reliability of a class of vacuum electronic devices, such as X-ray tubes. It has been suggested that electron field emission from negatively charged electrodes would precede and initiate such discharge. Heating and evaporation of material upon field emission would cause dense plasma to develop in periods of nanoseconds. High-pressure plasma would expand from the cathode, eventually bridging the gap. Nevertheless, the very reason for the unredictable initial development of discharge events after long periods of reliable operation is still matter of debate. Experience from industrial processes suggests hydrocarbon contamination to degrade the electric stability of high-voltage gaps. While former attempts aimed at explaining high field emission by carbonaceous 2D structures or surface resonance effects, this paper discusses whether 3D structures may grow slowly, until their evaporation in a matter of nanoseconds. Similar to the production of carbon nanotubes, protruding structures might comprise carbon and, in addition, metallic nanoparticles, which would boost production of vapor during their explosion. The hypothesis was tested by scanning electron and energy-dispersive X-ray inspection of two cathodes of medical X-ray tubes, covered with metallic seed nanoparticles, which served as model systems. A third cleaner cathode was inspected for comparison. Although certain suggested conditions of carbon feed, elevated substrate temperature and nanoparticle contamination of the surfaces were met, images showed only a very weak sign of growth of suspicious carbon structures. It seems, therefore, unlikely that CNT-like structures are a major cause of high-voltage breakdown between electrodes of X-ray tubes.

2016 ◽  
Vol 109 (20) ◽  
pp. 203504 ◽  
Author(s):  
M. Syamsul ◽  
Y. Kitabayashi ◽  
D. Matsumura ◽  
T. Saito ◽  
Y. Shintani ◽  
...  

1968 ◽  
Author(s):  
W. R. Bell ◽  
M. J. Mulcahy ◽  
F. Y. Tse ◽  
A. Watson

1970 ◽  
Author(s):  
Michael J. Mulcahy ◽  
Philip C. Bolin ◽  
William R. Bell ◽  
Frank Y. Tse

2020 ◽  
Vol 15 (04) ◽  
pp. P04022-P04022
Author(s):  
K. Woodruff ◽  
J. Baeza-Rubio ◽  
D. Huerta ◽  
B.J.P. Jones ◽  
A.D. McDonald ◽  
...  

1971 ◽  
Vol 15 ◽  
pp. 285-294 ◽  
Author(s):  
J. H. McCrary ◽  
Ted Van Vorous

Recently developed, miniature, steady state, field emission tubes are finding application in several areas of x-ray analysis. These tubes require only a high voltage, low current power supply to produce relatively intense beams of x-rays. Since anodes can be fabricated from almost any element, and since the tubes can be operated at potentials up to about 70 kV, many different output x-ray spectra are available. Miniaturized battery operated x-ray sources of this type, occupying a volume of about one liter, have several advantages over radioisotope sources. These include cost, safety, and controllable output spectra and intensity. X-ray sources for energy dispersive fluorescence analyzers are designed so that no scattered characteristic radiations will interfer with the analysis of the sample fluorescence. Sources which are essentially monoenergetic can be fabricated for use in non-dispersive x-ray fluorescence analyzers. Because of the intensity and safety of the field emission tubes, such analyzers can be made which are sensitive while compact, portable, and inexpensive. In x-ray absorption analysis the measurement of absorption edge jump ratios provides a quantitative measure of sample impurities. Field emission tubes whose output spectra consist primarily of bremsstrahlung are particularly well suited to such measurements. The techniques involved in using these tubes in x-ray analysis are described.


1967 ◽  
Vol 14 (8) ◽  
pp. 443-449 ◽  
Author(s):  
C.G. Englefield ◽  
V.J. Harwood ◽  
L.W. Toso

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