Das Neutralgasprofil und die Elektronentemperatur in der Freifallsäule bei hohem Ionisationsgrad

Abstract

The neutral gas flux from the wall into the columnconnected with the ion flux to the walland the anisotropy of the velocity distribution of the neutral gas are included into the theory of the steadystate positive column. d/Z, and vRo/vo occur as characteristic parameters. d denotes the radius of the column, 1, the mean free path of the neutral atoms for ionization. v,, the mean velocity of the neutral atoms re-emitted from the wall, vo = (2kT,/M)1'2, M the ion mass, T, the electron temperature. On the axis the neutral gas density N , is decreasing, if d/Z, is rising. At the wall N , is increasing for vno < w,, but it is almost constant or decreasing for v, , w 27, a t the same time. I n the plasma the total number of the atoms and the ions is taken as constant. In the case of small vlto the degree of ionization is high only for d > I,. However, it is already high for d w 1, in the case of high v,,,. Therefore. the radial profiles of the neutral gas densities of different gases in a column can differ from each other. Almost full ionization can be reached near the axis. These results hold, too, if the initial velocity of the ions and a magnetic field are taken into account. all,,, the degree of ionization, and the electron temperature are given as functions of the electric power input and of the total number of the neutrals and the ions. The velocities of the re-emitted atoms depend on the accomodation coefficient of the ions recombining a t the wall. With rising d/Z, an increasing number of the neutral atoms is re-emitted with superthermal velocities and the total number of the neutrals and the ions can be decreased. The anisotropy of the velocity distribution of the neutral atoms and the ions must be taken into account for the interpretations of spectroscopical measurements.

Neutral gas depletion in low temperature plasma

“…Similar expressions have been presented in [16,21]. Following equation ( 94), we express the neutral particle flux density at the wall as…”

“…The recombining ions carry a high kinetic energy upon hitting the wall-an energy they acquire while they move towards the wall across the sheath. A re-emitted neutral atom can carry part of the kinetic energy of the impinging ion, according to the accommodation coefficient, which causes an effective gas heating [20,21,57,66]. In this paper, we neglect this source of gas heating.…”

“…As is common in the literature, neutral gas depletion is termed neutral depletion in this paper. Neutral depletion in gas discharges has already been addressed theoretically and many features were unfolded in early studies [13][14][15][16][17][18][19][20][21][22][23][24][25][26]. Allen and Tonemann related in 1954 the phenomenon of current limitation in a low pressure arc to neutral depletion [14].…”

The Theory of the Low Pressure Discharge in the Strong Ionization Regime

“…181 and T O R V~N [13] showed that ions with vanishing initial velocity do not reach the interior of the column. t-1) to now ti non-vanishing initial ion velocity has not heen considered in the theory of the positive colunin for the free fall regime self-consistently (IASC:MUIR and TOXKS [ 121, ZESDIS ["I, VALENTINI [ 16,173). I n the following paper the system of intepo-differential eyiiations for the positive column iindei* free fall condition4 is derived taking into accoiint 1Joth the initial velocities of the ioiiq and the neiitral gas depletion by ionization.…”

Features of arc discharges applied to population inversion in lasers on ArII and ArIII ions

“…Влияние ионизации на распределение атомов в дуговом разряде низкого давления теоретически рассмотрено в работе [13]. С увеличением тока разряда возрастает температура всех частиц в плазме.…”