DIAGNOSTICS OF MULTICOMPONENT ELECTRIC ARC PLASMA

A.I. Cheredarchuk, V.F. Boretskij, A.N. Veklich Taras Shevchenko Kiev National University, Kiev, Ukraine E-mail: [email protected]

The plasma parameters of electric arc discharge in a gas flow between copper electrodes were investigated. The electrical conductivity of copper-argon and copper-carbon dioxide plasma was calculated. It was found that at low temperatures (5000 K

1. INTRODUCTION Ne(r) in discharge at 30 A were obtained from width of The electric arc between evaporated electrodes has spectral lines CuI 448.0 nm, broadened due to the quadratic diverse technological applications. It is well known that Stark effect. In the case of low current (3.5 A) absolute electrode vapours have a determining influence on intensity of CuI 465.1 nm spectral line was used. properties of arc plasma. The insignificant impurity N , m-3 (about 1 %) of electrode metal vapour appreciably j CO 2 changes plasma parameters of the discharge in a rather CO wide temperature range [1]. Unfortunately the influence O O e of metal impurity on the plasma of free burning electric 1E23 2 C arc discharge in different working gases is not O+ experimentally investigated in detail yet. The main aim of this study is a development of complex diagnostics techniques of determination of 1E20 plasma parameters of electric arc discharge in a gas flow between copper electrodes.

+ CO 2. TRANSPORT PROPERTIES C 2 T, K 1E17 OF THERMAL PLASMA 5000 10000 15000 20000 In calculations of the transport properties of thermal plasma it is necessary to know the proportion between Fig. 1. CO2 plasma composition plasma components at a constant pressure. The method of -3 Nj, m calculation of CO2 − Cu (or Ar − Cu) plasma composition CO 2 was discussed earlier [2]. The content of copper we CO O determined as XCu=(NCu+NCu+)/Nall. As examples in e 1E23 Fig. 1-2 the compositions of CO2 plasma as well as C O plasma mixture CO2-10% Cu are shown. One can see that 2 copper vapours play key role in ionization processes in Cu C+ wide temperature range. O+ At the next stage we can determine the electrical 1E20 conductivity of such plasma mixtures. It can be Cu+ σ e obtained according to Grad’s expression [3-4]: 22 CO en υ >< 2 T, K σ = e . (1) 1E17 e 2 5000 10000 15000 20000 me νυ >< For argon and argon-copper mixture the Frost’s Fig. 2. Plasma composition of CO2 and 10% Cu mixture expression [5] for electrical conductivity was also used: 4 en ∞ ⎛υπ 42 f ⎞ In Fig. 3 the radial distributions of temperature and σ F = e ⎜ M ⎟dυ, (2) 3 Tk ∫⎜ ν F ⎟ electron density in argon arc discharge are shown. Two b 0 ⎝ ⎠ essentially different modes of arc operation are observed F where fM – distribution function, ν – function of at arc current 3.5 A (see Fig. 3, a and Fig. 3, b). collisions electron with heavy particles. The obtained electron density and temperature in plasma as initial data were used in the calculation of 3. EXPERIMENT plasma composition in the assumption of local The arc was ignited in argon or carbon dioxide flow of thermodynamic equilibrium (LTE). In Fig. 4 the radial 6 slpm between the end surfaces of non-cooled copper electro- distributions of plasma component in argon arc discharge des. The diameter of rod electrodes was of 6 mm, the are shown. One can see that two modes of arc operation at discharge gap was of 8 mm, and the arc current was 3.5 and arc current 3.5 A (see Fig. 4, a and Fig. 4, b) differ 30 A. The radial temperature profiles T(r) in plasma were considerably by copper concentration in discharge gap. In obtained from intensities of CuI spectral lines by the Fig. 5 the radial distributions of copper content in such Boltzmann plot techniques using previously selected discharges and electrical conductivity obtained according spectroscopic data. The radial profiles of electron densities to expression (1) or (2) are shown. PROBLEMS OF ATOMIC SCIENCE AND TECHNOLOGY. 2011. № 1. 167 Series: Plasma Physics (17), p. 167-169. We should note that electrical conductivity essentially We studied plasma of arc discharge in carbon dioxide depends on plasma temperature. It is natural that this flow too (Fig. 6). In Fig. 7 the radial distributions of copper conductivity is raised with a current increasing up to 30 A. content in such discharges and electrical conductivity One can see that the temperature growth is noticeable in such obtained by Grad’s method (1) are shown. It was found in arc discharge (see Fig. 3, c). Similar behavior of electrical our previous investigations that plasma discharge in carbon conductivity is observed in two modes of arc operation at arc dioxide flow at arc current 30 A is not in equilibrium [2]. current 3.5 A. The decreasing of copper content (see We developed the calculation technique of the non-LTE Fig. 5, b) naturally leads to the temperature growth (see plasma composition. But the detail consideration of this Fig. 3, b) in the arc discharge. Therefore we observe in this problem is out of the frame of this work. case the not considerable increasing of electrical conductivity obtained by both Grad’s and Frost’s methods as well (see N , m-3 Fig. 5, a and Fig. 5, b). So, we must note once again that j Ar copper vapours play key role in this plasma source. 1E24 T, K N , m-3 e Cu 9E20 1E22 6500 N 6E20 e e + 1E20 Cu

6000 3E20 1E18 Ar+ 5500 T 01r, mm

012 a r, mm -3 N , m j Ar a 1E24 T, K N , m-3 e 9E20 1E22 + 6500 Cu e T 6E20 Cu N 1E20 e 6000 3E20 Ar+ 1E18

5500 012 r, mm

012 b r, mm -3 N , m j Ar b 1E24 8500 T, K N , m-3 e Cu+ e 1E22 1E22 Cu T N 8000 e + 1E20 Ar

1E18 7500

024 r, mm 7000 1E21 024 c r, mm Fig. 4. Radial profiles of plasma components in discharge c gap in argon flow at arc currents 3.5 A Fig. 3. Radial profiles of temperature and electron (a, b – two modes of arc operation) and 30 A (c) density in discharge in argon flow at arc currents 3.5 A (a, b – two modes of arc operation) and 30 A (c) 168 X , % between copper electrodes was developed. The electrical Cu σ, A/(V·m) 0.9 conductivity of copper-argon and copper-carbon dioxide 350 plasma was calculated. It was found that at low Eq.(1) temperatures (5000 K< T <9000 K) the electrical Eq.(2) conductivity considerably depends on the amount of 0.6 copper in plasma. X Cu 300 T, K N , m-3 e 9E26

6500 0.3 6E26 N e 250

6000 3E26 012 r, mm

a T X , % 5500 Cu σ, A/(V·m) 0.9 01 Eq.(1) 500 r, mm Eq.(2) Fig. 6. Radial profiles of temperature and electron density 0.6 in discharge in carbon dioxide flow at arc current 3.5 A 400 X , % Cu

σ, A/(V·m) 0.9 180 0.3 300 Eq.(1) X Cu 0.6 200 150

012 r, mm

b 0.3 X X , % Cu 120 Cu σ, A/(V·m)

1000 Eq.(1) 01 r, mm 1.4 Eq.(2) Fig. 7. Radial profiles of copper content and electrical conductivity in discharge gap in carbon dioxide flow at arc X 800

Cu current 3.5 A 0.7 REFERENCES

600 1. A. Gleizes, J.J. Gonzalez and P. Freton // J. Phys. D: Appl. Phys. 2005, v. 38, p. R153–R183. 0.0 2. I. L. Babich, V.F. Boretskij, A.N. Veklich // Problems 024 r, mm of Atomic Science and Technology. Series “Plasma c Physics” (14). 2008, N 6, p. 171-173. 3. V.M. Zhdanov. Transport phenomena in multicomponent Fig. 5. Radial profiles of copper content and electrical plasma. M: “Energoatomizdat”, 1982 (in Russian). conductivity in discharge gap in argon flow at arc currents 4. S.S. Mankut, A.M. Veklich, P.V. Porytskyy //Bull. of the 3.5 A (a, b – two modes of arc operation) and 30 A (c) Univ. of Kiev. Ser. “Phys.&Math”. 2006, N 3, p. 358-365. CONCLUSIONS 5. M. Mitchner, Ch. Kruger. Partially ionized gases. M: “Mir”, 1976 (Russian translation). The complex diagnostics technique of determination of plasma parameters of electric arc discharge in a gas flow Article received 01.10.10 ДИАГНОСТИКА МНОГОКОМПОНЕНТНОЙ ЭЛЕКТРОДУГОВОЙ ПЛАЗМЫ А.И. Чередарчук, В.Ф. Борецкий, А.Н. Веклич Исследовались параметры плазмы электродугового разряда в потоке газа между медными электродами. Рассчитана электропроводность плазмы медь-аргон и медь-углекислый газ. Установлено, что при низких температурах (5000 K < T < 9000 K) электропроводность существенно зависит от количества меди в плазме.

ДІАГНОСТИКА БАГАТОКОМПОНЕНТНОЇ ЕЛЕКТРОДУГОВОЇ ПЛАЗМИ А.І. Чередарчук, В.Ф. Борецький, А.М. Веклич Досліджувалися параметри плазми електродугового розряду у потоці газу між мідними електродами. Розраховано електропровідність плазми мідь-аргон та мідь-вуглекислий газ. Встановлено, що при низьких температурах (5000 K < T < 9000 K) електропровідність суттєво залежить від кількості міді в плазмі. 169