The Faraday dark space of a He glow discharge

1988 ◽  
Vol 63 (1) ◽  
pp. 60-63 ◽  
Author(s):  
Yu. M. Kagan ◽  
C. Cohen ◽  
P. Avivi
Keyword(s):  
Glow Discharge ◽  
Dark Space

scholarly journals Atomic hydrogen III—The energy efficiency of atom production in a glow discharge

1937 ◽  
Vol 163 (914) ◽  
pp. 424-454 ◽  
Keyword(s):  
Glow Discharge ◽  
Closed System ◽  
Atomic Hydrogen ◽  
Empirical Relation ◽  
Power Input ◽  
Degree Of Dissociation ◽  
Recombination Processes ◽  
Dark Space ◽  
The Difference ◽  
Three Body

There seems to have been a tendency amongst workers on the use of the glow discharge as a source of atomic hydrogen to regard the current or power as determining the degree of dissociation of the gas, i. e. the equi­librium H 2 ⇌2H. It is clear, however, that the discharge itself determines only the rate of production of atoms, whereas the degree of dissociation depends also on the rate of removal of atoms by pumping and by recombina­tion processes which are independent of the discharge. The two homogeneous recombination processes are those resulting from three-body collisions be­tween three atoms and between two atoms and a molecule; in addition, there is a heterogeneously catalysed reaction in which the walls of the tube act as the energy acceptor. Attempts to connect electrical conditions with degree of dissociation have been made by Crew and Hulburt (1927) and by Wrede (1929), but the above remarks show that only empirical relationships can be hoped for. In Crew and Hulburt’s experiments, the degree of dissociation was estimated by measuring the change of pressure in a closed system on passing a discharge. A correction for temperature was applied, which was based on the erroneous idea that the rise of temperature due to discharge in helium is about the same as that in hydrogen at the same pressure and power input. The method of determining the pressure depended on an empirical relation between pressure and the length of the cathode dark space in an auxiliary discharge connected to the main system ; but since the cathode dark space has not a sharply defined boundary, and the degree of dissociation is calculated from the difference of two pressures measured in this way, considerable error is possible. Furthermore, in a closed system, the rate of production of atoms is equal to the rate of recombination; and since these workers relied on a water-on-glass film to inhibit heterogeneous recombination, and as the power input was 200-1000 W, the catalytic activity of the walls must have been very variable and large (Part II). Crew and Hulburt’s curves con­necting degree of dissociation with pressure and power input cannot, there­fore, be credited with quantitative significance.

scholarly journals Influence of Electron Injection on the Characteristics of a Hollow Cathode Glow Discharge

2021 ◽  
Keyword(s):  
Glow Discharge ◽  
Hollow Cathode ◽  
Discharge Current ◽  
Cathode Surface ◽  
Electron Flow ◽  
Glow Discharge Plasma ◽  
Cathode Cavity ◽  
Main Discharge ◽  
Dark Space ◽  
Gas Pressures

The article presents the results of experimental studies of a glow discharge with a hollow cathode in helium and argon gases using an auxiliary discharge as an electron emitter. The authors proposed to make the electrode common for both discharges in the form of a cylindrical metal mesh. The advantage of this design is explained as follows. The connection between the discharges is carried out through holes in the grid with a geometric transparency of 0.2, which makes it possible not only to smoothly control the glow discharge current, but also to enhance the discharge current. Plasma is known to be one of the most efficient electron emitters; however, its use as a cathode in devices with a glow discharge at low gas pressures is complicated by the fact that a grid with small holes is required to separate the electron flow from the plasma, and it is impractical to use such a system in view of low mechanical strength of the grid Since the hollow cathode works effectively at low gas pressures, the release of an electron flux from the plasma of some auxiliary discharge is possible with much larger holes in the grid separating the plasma and the hollow cathode cavity. In this case, the grid can be made such that it can withstand sufficiently high thermal loads and can operate in typical discharge modes with a hollow cathode. The injection of electrons into the cathode cavity of the glow discharge changes the radial distribution of the glow intensity, the width of the cathode dark space, and other parameters of the plasma in the cathode cavity. The influence of electrons penetrating from the auxiliary discharge into the cathode cavity of the main discharge becomes significant when the current of these electrons is comparable to or exceeds the current of electrons leaving the grid cathode surface as a result of γ-processes. In parallel with the measurement of the optical and electrical characteristics of the hollow cathode glow discharge plasma, measurements of the electron concentration were carried out by the microwave sounding method. The entire current of the auxiliary discharge penetrates into the cavity of the main discharge; however, after acceleration in the cathode dark space, the electrons penetrating from the auxiliary discharge ionize gas atoms and noticeably increase the current of the main discharge. Additional ions formed due to the ionization of the gas by the injected electrons knock out new electrons from the cathode surface, which makes it possible to increase the discharge current.

Some investigations of gas discharges by means of an exploring electrode

1927 ◽  
Vol 23 (5) ◽  
pp. 531-541 ◽  
Author(s):  
K. G. Emeléus
Keyword(s):  
Glow Discharge ◽  
Electric Field ◽  
Electron Current ◽  
Negative Glow ◽  
Gas Discharges ◽  
Slow Group ◽  
Dark Space ◽  
Current Densities ◽  
Fast Group

The glow discharge between cold aluminium electrodes in air, oxygen, nitrogen and hydrogen has been analyzed by Langmuir's method, for pressures between 0·1 and 0·4 mm. Hg, current densities of from 0·02 to 0·2 mA./sq.cm., and applied potentials between 300 and 700 volts. An annular exploring electrode has been used. It has been found that whilst practically the whole fall of potential is localized across the cathode dark space at the lower pressures, a fall of as much as 40 volts can exist across the remainder of the discharge at the higher pressures. Reversal of the electric field has been found in the negative glow, and in certain cases in the Faraday dark space, when conditions are favourable for passage of an electron current by diffusion against the field. In several instances the negative glow was at a higher potential than the anode. Two groups of electrons occur in the negative glow, together with a single fast group at the anode boundary of the cathode dark space, and a single slow group in the Faraday dark space.

scholarly journals The energy distribution among the positive ions at the cathode the glow discharge through gases

1932 ◽  
Vol 137 (833) ◽  
pp. 662-676 ◽  
Keyword(s):  
Glow Discharge ◽  
Energy Distribution ◽  
Potential Drop ◽  
Potential Method ◽  
Full Potential ◽  
Cathode Fall ◽  
Positive Ions ◽  
Dark Space ◽  
Positive Ion ◽  
Made In

The energy distribution among the positive ions which strike the cathode of the glow-discharge through gases is of some importance in the theory of the phenomenon, and as very little is known about the mean-free-paths of ions in gases it is difficult to make an estimate of this distribution. Attempts have been made in the past to measure this quantity by perforating the cathode and applying retarding potentials to the ions which penetrate through. The positive ion photographs obtained by the parabola method of Sir J. J. Thomson give information concerning the distribution in a strongly abnormal discharge. These last, and observations of the Doppler effect in canal-rays, suggest that there are particles present with energies corresponding with a fall through the full potential drop across the dark-space, while the retarding potential measurements of Von Hippel show a sharp upper limit to the energy at between 0·3 and 0·5 of the total cathode fall. The dark-space stretches over 20 to 100 molecular free-paths, so that if ions are present with the full energy corresponding to the cathode fall they must have relatively long free-paths in the dark-space. We have carried out measurements of the energy distribution among the positive ions which penetrated through a slit in a plane cathode into an evacuated space beyond, by a retarding potential method and by the method of focussing at 127° 17' in an inverse first power electrostatic field.

Effect of Dark Space in RF Glow Discharge on Plasma Etching Characteristics

1978 ◽  
Vol 17 (11) ◽  
pp. 2071-2072 ◽  
Author(s):  
Seitaro Matsuo ◽  
Yumiko Takehara ◽  
Akira Ozawa
Keyword(s):  
Glow Discharge ◽  
Plasma Etching ◽  
Rf Glow Discharge ◽  
Dark Space

The hollow-cathode effect and the theory of glow discharges

1954 ◽  
Vol 224 (1157) ◽  
pp. 209-227 ◽  
Keyword(s):  
Glow Discharge ◽  
Electric Field ◽  
Current Density ◽  
Hollow Cathode ◽  
Elementary Theory ◽  
Secondary Electron Emission ◽  
Space Charge Density ◽  
Cathode Fall ◽  
Space Length ◽  
Dark Space

The nature of the processes in the cathode dark space and the negative glow of a glow discharge is not well understood. Moreover, the existing theory leading to relations between the cathode fall in potential, the current density, the width of the dark space and the electric field distribution in it is based on dubious assumptions and does not indicate the important physical processes in operation. Thus further experimental evidence would be valuable in developing the theory. By exploring the electric field between two plane-parallel cathodes with an electron beam, and observing simultaneously the other discharge parameters, new information was obtained. A double (hollow) cathode was used because in a conventional glow discharge the dark space, cathode fall and current density are interdependent; here the cathode separation controls the width of the dark space. When the separation is sufficiently reduced the two negative glows coalesce and the light emitted as well as the cathode current density rise greatly. This is the hollow-cathode effect. Results show that the field in the two dark spaces of a hollow cathode falls linearly with the distance from the cathode, and thus the net space-charge density is constant, as it is known to be in the conventional discharge. From the same observations the dark-space length is found. The conclusions drawn from these results lead to an elementary theory which covers both the hollow and the conventional glow discharge in various gases as indeed it should, since with increasing cathode separation the first goes over into the second type. The main feature is the contribution of the ultra-violet quanta from the glow to the photo-electric emission from the cathodes which is regarded as the essential factor in secondary electron emission. Another result comes from a reconsideration of the motion of positive ions in the dark space based on atomic beam studies and the modem theory of elastic collisions between ions and atoms. The discrepancy between earlier experiments showing that ions of energy of the order of the cathode fall in potential arrive at the cathode and classical calculations leading to low ion energies is resolved by allowing for small-angle scattering and charge transfer.

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