Vol. 1, No 2, 1995 pp. 114 - 126
UDC 533.92
A STUDY OF BASIC PROPERTIES OF HIGH-PRESSURE AND LOW TEMPERATURE THERMAL ARGON PLASMA WITH SODIUM AS ADDITIVE
N.V. Novaković1, B.S. Milić2, S.M. Stojilković3
1Faculty of Philosophy, Dept. of Physics, P.O.B. 91, 18001 Niš
2Faculty of Physics, P.O.B. 550, 11001 Belgrade
3Faculty of Electronics, Niš
Abstract.Results of a theoretical evaluation of number densities and electri¬cal conductivity, regarded as functions of pressure and temperature, for high-pressure (0.1 MPa to 2.5 MPa) and low-temperature (2000 K to 20000 K) argon plasma containing up to 10% of added sodium are presented. The numerical cal¬culations were based on the assumption that the system is kept under constant pressure and temperature and that it attained local thermodynamical equilib¬rium. Use was made of a previously derived modified Debye radius which al¬lowed to regard the plasmas investigated as weakly non-ideal and to calculate their composition from a set of Saha equations for the relevant ionization stages of both Ar and Na. The results arrived at were compared to those for pure argon plasma obtained by the same evaluation methodology. It was found that the addition of little as 1% of Na profoundly alters the properties of the plasma. The electrical conductivity is enhanced, with respect to the values in pure Ar plasma, by about two orders of magnitude below 10000 K, and by about half an order of magnitude above that temperature, provided that the pressure is not less than 0.5 MPa. For pressures around 0.1 MPa, the electrical conductivity in pure argon plasma is somewhat greater at higher temperatures (above 14000 K) than with 1% of sodium added. This is due to a specific change in the pressure dependence of the electrical conductivity: the p-1/2-dependence specific for pure argon plasma abruptly switches to p1/2-dependence observed in alkaline vapours if just 1% of Na is added. Further increase of the conductivity, as the amount of sodium is augmented to 10%, is comparatively small and noticeable only be¬tween 10000 K and 14000 K. Physical factors bringing about these features are discussed.
PRILOG IZUČAVANJU OSNOVNIH OSOBINA TERMALNE ARGONOVE PLAZME SA DODATKOM NATRIJUMA NA VISOKIM PRITISCIMA I NISKIM TEMPERATURAMA
Prikazani su rezultati jednog teorijskog izučavanja koncentracije konstituenata i elektroprovodnosti u funkciji pritiska i temperature kod plazme visokog pritiska (od 0,1 MPa do 2,5 MPa) i niske temperature (od 2000 K do 20000 K) formirane u argonu sa dodatkom do 10% natrijuma. Numerička izračunavanja zasnivala su se na pretpostavci da se sistem održava na konstantnom pritisku i konstantnoj temperaturi i da je dostignuto stanje lokalne termodinamičke ravnoteže. Korišćen je ranije nađeni modifikovani izraz za Debye-ev radijus, što je omogućilo da posmatrane plazme budu tretirane kao slabo neidealne i da se, shodno tome, njihov sastav odredi na osnovu sistema Saha jednačina za relevantne jonizacione stadijume Ar i Na. Dobijeni rezultati su upoređeni sa onima za plazmu u čistom argonu, izračunatim istom metodologijom. Nađeno je da dodavanje i samo 1% natrijuma bitno menja transportne osobine plazme. Ispod 10000 K elektroprovodnost se povećava, u poređenju sa onom kod čistog Ar, za oko dva reda veličine, a iznad te temperature za oko pola reda veličine, ukoliko pritisak nije manji od 0,5 MPa. Za pritiske oko 0,1 MPa, elektroprovodnost u plazmi čistog argona je na višim temperaturama (iznad 14000 K) nešto veća nego u prisustvu 1% natrijuma. Ovo se javlja zbog specifične izmene u zavisnosti elektroprovodnosti od pritiska: već pri dodatku 1% natrijuma, zavisnost σ  p-1/2 karakteristična za plazmu u čistom argonu naglo se menja i postaje σ  p1/2, što je tipično za čiste alkalne pare. Dalje povećavanje elektroprovodnosti, kad se količina dodatog Na uvećava do 10%, srazmerno je mala i primetna je samo između 10000 K i 14000 K. Prodiskutovani su fizički razlozi za ovakvo ponašanje.