Cathode erosion in inert gases: The importance of electrode contamination

Szente, R. N.; Munz, R. J.; Drouet, M.

doi:10.1007/bf01015830

Cited by 32 publications

(18 citation statements)

References 15 publications

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“…Accordingly, in the stationary experiments, the cathode surface was covered with a much thicker oxide layer than that in the nonstationary experiments. As has been shown in [21][22][23][24], thick oxide layers on the cathode surface decrease the mobility of a cathode spot and make its motion discontinuous (characterized by n > 1), simultaneously increasing erosion, and, conversely, thin oxide layers contribute to a uniform motion of the arc spot (n = 1) with a reduced erosion. Since n = 1 was taken for all the experiments, we were to obtain overstated (relative to the real ones) values of the current density.…”

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confidence: 90%

“…As our experiments show, the motion of the arc becomes less stable and more discontinuous for low magnetic fields, which is attributable to the dominance of the specific "surface" resistance to the spot motion [21,22] over the ponderomotive force I × B moving the arc. Therefore, for low magnetic fields, the real time of the immobile state of the arc spot can be much longer than that calculated by us from the measurements of the average velocity and quite sufficient for fusion of the basic substrate of the electrode.…”

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confidence: 92%

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Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. I. Current density

Bublievskii

Marotta

Esipchuk

et al. 2005

J Eng Phys Thermophys

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A new procedure of determination of the effective density of the current in a nonstationary arc spot with the use of thermophysical and spectroscopic measurements has been proposed and tested. The procedure is based on recording of the critical cathode temperature corresponding to the instant of sharp increase in the intensity of the CuI λ = 5218 A° atomic spectral line, which coincides with the beginning of intense emission of a copper vapor from the spot, according the hypothesis proposed. New results are compared to those obtained earlier by purely thermophysical methods.Introduction. The density of the current in an arc spot is one of the most important parameters determining the erosion and service life of the electrodes in electric-arc gas heaters (EAHs) and other arc devices. One traditionally calculates it from the data of measurements of the current and the dimensions of the arc spot, taking the symmetry of the latter to be circular, i.e., j = 4I/πd 2 . Two methods are usually used to measure the diameter: those of autographs and high-speed photorecording. In the autograph method, the dimension of the emitting region of the spot is taken to correspond to the size of the craters left by it, whereas in the method of high-speed recording, it is taken to correspond to the dimensions of the luminous region of the cathode plasma [1, 2].As has been revealed with the modern technique of optoelectronic recording with a high temporal and spatial resolution, the arc spot on a cold cathode has a very dynamic structure and consists of a large number of individual short-lived microspots that have a complex hierarchic structure and are in continuous motion. Moreover, as the recording technique is improved, this hierarchy increasingly expands toward revealing the finest details of the internal microstructure. Such a situation makes determination of the current-conducting zone of the spot very difficult and dependent on how the situation observed corresponds to the dimension of the zone [2]. In [3], an attempt was made to measure the average dimension of this zone by moving the spot slowly through an insulating gap of a special current sensor divided by this gap into two halves in recording a change in the current in each half. However, the presence of such a gap can substantially distort the shape and dimensions of the conducting zone; therefore, this method applies only to specific conditions of slowly moving spots with a size much larger than the gap size, because of which Szente et al. used it for a plasma cutting arc. In [4,5], traversal of a special linear magnetic sensor by the spot instead of the traversal of an insulated slot was used for such measurements in an electric-arc unit with a magnetic movement of the arc, which introduced no disturbances into the spot itself. However, such a method gives only the linear current density, which is difficult to convert to the real one without knowing the spatial current distribution. Therefore, we proposed that the concept of the effective current density in the arc spot...

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confidence: 92%

Investigation of the parameters of a nonstationary arc spot on a copper cathode by the thermospectroscopic method. I. Current density

Bublievskii

Marotta

Esipchuk

et al. 2005

J Eng Phys Thermophys

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“…In magnetically rotating arc plasma generators, three arc modes, namely rigid, distorted, and diffuse, have been previously observed. The arc column that rotates around the electrode in a rigid shape is classified as the rigid mode, while the arc column that rotates around the electrode in a constantly changing shape is identified as the distorted mode . When the arc column evolves from a constricted column to a diffuse plasma cloud that occupies the chamber's entire cross section, the arc column is deemed to be operated in the diffuse mode …”

Section: Introductionmentioning

confidence: 99%

Observation of arc modes in a magnetically rotating arc plasma generator

Wang

Cui

Zhang

et al. 2017

Contrib. Plasma Phys

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An arc plasma can present various forms under the influence of an external magnetic field. In this study, a magnetically rotating arc plasma generator has been developed to produce three arc modes, namely rigid arc, distorted arc, and diffuse arc, which are obtained by controlling the gas flow rate. The evolution of these arc modes are experimentally studied and discussed. Results show that, as the gas flow rate increases, the arc mode is first transformed from the rigid to the distorted mode, and then to the diffuse mode. Comparisons show that the location of the arc attachment is a key factor in determining the rigid and distorted modes. The diffuse arc is observed under larger gas flow rates, but the completely diffuse arc can exist only within a narrow range of gas flow rates. Compared to the distorted arc, the diffuse arc has not only better stability but also a wider high-temperature plasma zone, which indicates that the diffuse mode may be more useful in industry. KEYWORDSarc attachment, arc mode, arc voltage, magnetically rotating arc plasma 1

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“…The early studies, however, were restricted to laminar flow situations and most real plasma reactors represent turbulent characteristics. To solve this problem, a standard or a modified K-ε turbulence model [2] was employed, which was assumed to be still valid for plasma jets. Up to the present time, the scientific basis of these operations has been concerned with 2D fluid turbulence models [3][4][5] to avoid a complicated computation.…”

Section: Introductionmentioning

confidence: 99%