Research Unit of Ionized and Reactives Media Studies (EMIR)
National School of Engineering of Monastir
5000 Rue Ibn Jazzar
Monastir 5035

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Effect of a bidirectional coupling of an LTE arc column to a refractory cathode in atmospheric pressure argon

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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Permanent Identifier (DOI)
Permanent Identifier (URI)
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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.
Plasma Medium Name
Plasma Medium Properties
Thermal plasma in the state of LTE except in the regions close to the electrodes.
Plasma Diagnostics Name
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.

Plasma Diagnostics Procedure

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.

Public Access Level
Contact Name
Baeva, Margarita
Contact Email

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