Study of negative glow and positive column regions of capillary HF discharge

Abstract

In the present thesis excitation mechanisms of helium atoms and ionization mechanisms of nitrogen molecules in He / N2 mixtures of y-mode HF capillary discharge were studied. Two discharge regions- negative glow and positive column were under investigation. Experiments were carried out at middle pressures, N2 fraction was varied in 0 - 0.5% range. From electrical parameters i-u characteristics at different N2 concentrations were recorded and phase shift between i and u was determined. On the basis of results of electrical measurements the electron density was calculated and the electric field strength in the positive column was determined. Discharge spectra as a function of discharge current, total pressure and N2 concentration were recorded. On the basis of spectral measurements the concentration of He metastable state atoms and the rotational temperature of N2+(B) state were calculated. Experimental results allowed to clarify the dominating He excitation and N2 ionization mechanisms. In the negative glow region: (i)He is excited dominantly via He2+ recombination in reactions He2+ + e -> He* + He and He2+ + e + He -> He2* + He -> He* + 2He; (ii) N2+ ions are produced mainly via charge transfer reaction, He2+ + N2 -> N2+ + 2He. In the positive column region: (i) He excitation occurs mainly via electron impact with metastable state He atom Hem, Hem + e -> He* + e; (ii) N2 ionization occurs in Penning reaction, Hem + N2 -> N2+ + He.

Käesolevas doktoritöös uuriti heeliumi ergastusmehhanisme ja lämmastiku ionisatsiooni-mehhanisme He/N2 segus kõrgsagedusliku y-režiimi kapillaarlahenduse negatiivse helenduse ning positiivse samba piirkonnas. Plasma tekitati keskmistel rõhkudel, N2 sisaldust muudeti vahemikus 0 - 0.5%. Elektrilistest parameetritest mõõdeti volt-amper karakteristika ja faasivahe erinevatel N2 kontsentratsioonidel. Elektrimõõtmiste alusel leiti elektronide kontsentratsioon ning positiivse samba puhul määrati ka väljatugevus. Spektrid registreeriti sõltuvana voolutugevusest, N2 kontsentratsioonist ja kogurõhust. Spektraalmõõtmistulemuste põhjal leiti He metastabiilses seisundis olevate aatomite He(23S) kontsentratsioon, N2+ (B-X, 0-0) rotatsioonspektrit kasutades arvutati N2+ (B) rotatsioontemperatuur. Eksperimenditulemuste analüüsist järeldus uuritavates lahenduspiirkondades domineerivad He ergastus- ja N2 ionisatsioonimehhanismid. Negatiivses helenduses (i) toimub He ergastamine põhiliselt He2+ rekombinatsiooni-reaktsioonides, He2+ + e -> He* + He ja He2+ + e + He -> He2* + He -> He* + 2He, (ii) ioonid N2+ tekitatakse valdavalt laenguvahetusreaktsioonis, He2+ + N2 -> N2+ + 2He. Positiivses sambas (i) toimub He ergastamine elektronpõrkega He metastabiilses seisundis oleva aatomiga, Hem + e -> He* + e, (ii) ioonid N2+ tekivad Penningi reaktsiooni tulemusena, Hem + N2 -> N2+ + He.