Mechanism of ion flow generation in vacuum arcs

Barengolts, S. A.; Mesyats, G.; Shmelev, D. L.

doi:10.1134/1.1427117

Cited by 61 publications

(41 citation statements)

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“…Equa tions (6) were written for Ti n and Al n components with n = 0, 1, …, 4. Despite the simplified approach to describing ionization, these calculations of the com position of the ionized arc plasma give results that are quite consistent with the experimental data [7,10,13] and with detailed kinetic calculation data [14]. This allows us to hope that the proposed simple method will also yield at least qualitatively correct results for a dis charge plasma with a composite cathode.…”

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“…The arc current buildup is accompanied by an increase in the number of simultaneously oper ating cells of the cathode spot. For this reason, the ion flux parameters (the distribution of ion velocities and charges, ion erosion rate, ion current fraction) are independent or weakly depend on the arc current up to the kiloampere level [4][5][6][7].It was shown [8] that the elemental composition of the vacuum arc plasma almost coincides with the ele mental composition of the composite cathode. For this reason, the proposed model assumes that compo nents in the cathode spot of the composite electrode (in this case, Al and Ti) erode simultaneously and the relative rate of their erosion corresponds to their rela tive content and does not change with time.…”

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“…The radius of a the cathode spot cell was assumed to be 1 μm and the spot current density was taken equal to 10 8 A/cm 2 [4][5][6][7], which approximately corresponds to a double threshold current. The parti cle flux was determined by a preset specific erosion rate.…”

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Model calculation of the charge composition of a plasma in a vacuum-arc discharge with a composite cathode

2015

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Composite cathodes manufactured by mixing (sin tering or melting) various components in the desired proportion are widely used to obtain various func tional coatings by electric arc spraying. In particular, titanium-aluminum composite cathodes are used to deposit wear resistant and heat resistant coatings on cutting tools [1]. During spraying of a composite cath ode in a vacuum arc source material for multicompo nent ion deposition (implantation), the main task is to form a near surface layer with a certain stoichiometric composition on the processed substrate (target). For this reason, it is an important to know how the charge composition of ions of the initial components entering the vacuum discharge plasma changes as compared to the relative yield of these components from the cath odes of corresponding pure materials.The present Letter proposes a simple model for cal culating changes in the charge composition of a vac uum arc plasma in discharge with a composite cath ode. The results of model calculations are compared to recent experimental data [2,3]. Zhirkov et al.[2] pre sented the results of an experimental study of the mass and charge composition in a vacuum arc discharge plasma with a Ti 1 -x Al x (x = 0.16-0.7) composite cathode operating in a continuous mode. In [3], the mass and charge composition in a vacuum arc dis charge plasma had a cathode with a similar composi tion (Ti 0.67 Al 0.33 ), but operating in a pulsed discharge regime.The proposed model is based on the ecton mecha nism of vacuum arc cathode spot operation [4]. According to this mechanism, a vacuum arc plasma is formed as a result of the operation of separate cells (explosive emission centers) in the cathode spot of the vacuum arc. The arc current buildup is accompanied by an increase in the number of simultaneously oper ating cells of the cathode spot. For this reason, the ion flux parameters (the distribution of ion velocities and charges, ion erosion rate, ion current fraction) are independent or weakly depend on the arc current up to the kiloampere level [4][5][6][7].It was shown [8] that the elemental composition of the vacuum arc plasma almost coincides with the ele mental composition of the composite cathode. For this reason, the proposed model assumes that compo nents in the cathode spot of the composite electrode (in this case, Al and Ti) erode simultaneously and the relative rate of their erosion corresponds to their rela tive content and does not change with time. In addi tion, the results of Zhirkov et al. [2,9] show that ions of various sputtered components have almost identical velocities. The results of our recent model calculations [10] for a three component plasma showed that the drift velocities of ions with even significantly different masses (zirconium and deuterium) exhibit leveling as a result of strong ion-ion interaction in a dense near cathode plasma. For this reason, the proposed model assumes that ions of different components have the same velocity and, hence, the plasma can be described using the two temperat...

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Model calculation of the charge composition of a plasma in a vacuum-arc discharge with a composite cathode

2015

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“…This choice is related to the fact that the ionized plasma composition exhibits "quenching" within a distance of 10 μm from the cathode and then remains constant [12][13][14]. The angle of spherical cone expansion was determined from a comparison of the results of test calculations for k = 0 and the charge composition and average ion charge known for the arc operating on pure zirconium cathode [4].…”

Section: The Effect Of Cathode Deuteration On the Parameters Of Vacuumentioning

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The effect of cathode deuteration on the parameters of vacuum-arc plasma

2014

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A source of ions based on vacuum discharge is the main element of vacuum neutron generators (neutron tubes) [1]. The electrodes of this source-cathode and anode-contain the working gas (hydrogen isotopes) in occluded state. The evolution of deuterium and for mation of its ions takes place upon the initiation of a short time (~1 μs) spark arc discharge between the cathode and anode. This discharge is accompanied by erosion of the surface of electrodes, which leads to the generation of working gas ions and is a desired process, and by evaporation of the electrode base metal, which is a harmful side effect. Optimization of the working characteristics of an ion source-i.e., the specific ion yield (the ratio of the number of working gas ions to energy consumed per pulse of discharge), working life, and stability-requires adequate description of the discharge.The present Letter proposes a model for determin ing the influence of the relative content of deuterium in a zirconium cathode on the properties of vacuum arc discharge plasma. The model is based on the ecton mechanism of the vacuum arc cathode spot operation [2]. According to this mechanism, vacuum arc plasma is formed as a result of the operation of separate cells (explosive emission centers) in a cathode spot of the vacuum arc. At present, the existence of these cells is commonly accepted [2][3][4]. The arc current buildup is accompanied by growth in the number of simulta neously operating cells of the cathode spot. For this reason, the parameters of ion flux are independent or weakly dependent on the arc current up to a kiloam pere level [5].The cell current in a cathode spot amounts to sev eral amperes, and the current density at the base of a plasma jet is on the level of 10 8 A/cm 2 [2, 3], which is characteristic of the explosive electron emission. The possibility of realization of the explosive electron emission conditions in the cathode spot of vacuum arc has been discussed for a long time. However, at present, it can be ascertained that the interaction of dense near cathode plasma with microinhomogene ities on the cathode surface unavoidably leads to the initiation of explosive electron emission [6][7][8].According to the proposed model, the cathode spot of a deuterated zirconium electrode features simulta neous erosion of deuterium and zirconium. It is assumed that the ratio of erosion rates of these compo nents is determined by the degree of electrode satura tion with deuterium and does not change with the time. Most probably, these assumptions are not gener ally valid because of an extremely complicated charac ter of sorption and desorption of hydrogen isotopes and a sharp dependence of the rates of their diffusion and desorption on the temperature. Nevertheless, these premises are quite acceptable at the initial stage of operation of the ion source, when the electrodes are not strongly heated. Thus, cathode spots directly sup ply deuterium to vacuum arc plasma. In addition, we assume that plasma expansion is spherically symmet ric and, hence, a one ...

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Ignition and erosion of materials by arcing in fusion‐relevant conditions

Hwangbo

Kajita

Barengolts

et al. 2018

Contributions to Plasma Physics

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This study investigated the characteristics of arcing initiated on nanostructured fuzzy tungsten (W) surfaces in helium (He) plasmas. Under the same He plasma conditions, the relationship between arc voltage and current was characterized as linear due to plasma resistance across the He plasma from the target surface to the plasma source. Properties of the erosion caused by arcing were investigated by focusing on two parameters: arc current and fuzzy layer thickness. The erosion per charge was significantly dependent on the thickness of the fuzzy layer but did not depend on the arc current. Sample surface analysis revealed that drastic changes in arc spot grouping features were accompanied by the fuzzy layer thickness variation. The ecton model indicated that the erosion as ions does not play a main role, but mechanical destruction by momentum transfer from the explosive electron emission centre to neighbouring nanowires seems to enhance the erosion greatly.

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Mechanism of ion flow generation in vacuum arcs

Cited by 61 publications

References 10 publications

Model calculation of the charge composition of a plasma in a vacuum-arc discharge with a composite cathode

Model calculation of the charge composition of a plasma in a vacuum-arc discharge with a composite cathode

The effect of cathode deuteration on the parameters of vacuum-arc plasma

Ignition and erosion of materials by arcing in fusion‐relevant conditions

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