An appropriate coupling of an arc plasma column in the state of local thermodynamic equilibrium to a refractory
cathode necessarily involves the non-equilibrium boundary layer between them. A model has been developed that
combines a model of an equilibrium direct current arc plasma in atmospheric pressure argon with the assembly of a cathode made of tungsten and the boundary layer. A bidirectional coupling has been realized that allows us to consider a variable voltage drop across the boundary layer for different positions on the cathode. Results are obtained for arc currents between 10 and 150A in the cases of both a unidirectional and a bidirectional coupling. The results Show differences in the distributions of the temperature and the normal current density on the cathode surface, and the radial and axial distribution of the plasma temperature. Comparison with results of a fully non-equilibrium model of the arc plasma and experimental findings from optical emission spectroscopy show a fair agreement for currents, where the deviations from equilibrium in the arc column can be ignored. For arc currents beyond 100 A, the arc attachment on the cathode appears in two forms, which differ from each other in the distributions of the temperature and the normal current density on the cathode surface, whereas the values of the total arc voltage are close to each other.
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|Plasma Source Name|
|Plasma Source Specification|
|Plasma Source Properties|| |
The cathode is made of pure tungsten and has a radius of 1 mm in its cylindrical part and a length of 15 mm. The truncated conical tip has a vertex angle of 40° and a plateau with a radius of 0.2 mm. The anode is hemispherical with a flattened top and made of graphite. The arc is ignited in argon at atmopsheric pressure. Arc current values go up to 150 A.
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Thermal plasma in the state of LTE except in the regions close to the electrodes.
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|Plasma Diagnostics Properties|| |
The equipment consists of a spectrograph Acton SP2500 with a focal length of 0.5 m and an intensified CCD camera Princeton Instruments PI-MAX4. The triggering is controlled by a delay generator BNC Model 575 with optical outputs via optical fibers. The image of the arc is recorded by a high-speed video camera of the type IDT Motion Pro Y6. The arc is imaged by a spherical mirror on the entrance slit of the spectrometer with a width of 30 micrometers.
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The Emission spectra are radially resolved. They contain spectral and spatial side-on information about the arc. Absolute calibration is performed by a tungsten strip lamp placed at the position of the arc.
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Data and Resources
- Effect of a bidirectional coupling - Fig. 2csv
Current density and its components and voltage drop in the ionization layer...
- Effect of a bidirectional coupling - Fig. 3csv
Net heat flux to the cathode wall, constituents and electron temperature Te...
- Effect of a bidirectional coupling - Fig. 6acsv
Temperatures at a distance from the cathode tip 1 mm for an arc current of...
- Effect of a bidirectional coupling - Fig. 6bcsv
Temperatures at a distance from the cathode tip 2.5 mm for an arc current of...
- Effect of a bidirectional coupling - Fig. 6ccsv
Temperatures at a distance from the cathode tip 4 mm for an arc current of...
- Effect of a bidirectional coupling - Fig. 7csv
Axial distribution of the temperature an arc current of 142 A.
- Effect of a bidirectional coupling - Fig. 8acsv
Distribution of the temperature Tw and the normal current density jw along...
- Effect of a bidirectional coupling - Fig. 8bcsv
Dustribution of the voltage drop U and the absolute value of the electric...
- Effect of a bidirectional coupling - Fig. 9csv
Predicted arc voltage Uarc and its components Upl and U as functions of the...
- Effect of a bidirectional coupling- Fig. 10acsv
The distribution of the temperature Tw along the cathode for arc currents...
- Effect of a bidirectional coupling - Fig. 10bcsv
The distribution of the normal current density jw along the cathode for arc...