US3345280A

US3345280A - Method and apparatus for controlling glow discharge processes

Info

Publication number: US3345280A
Application number: US155210A
Authority: US
Inventors: Berghaus Bernhard
Original assignee: Ionon GmbH
Current assignee: Ionon GmbH
Priority date: 1960-11-28
Filing date: 1961-11-27
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03
Also published as: GB984963A; DE1417746A1

Description

Oct. 3, 1967 B. BERGHAUS 3,345,280

METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES Filed Nov. 27, 1961 4 Sheets-Sheet l INV ENT OR j BERN/MED BEPGHAUS ATTORNEYS Oct. 3, 1967 B. BERGHAUS 3,345,280

METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES I Filed NOV. 27. 1961 4 SheetsSheet 2 INVENT OR I i BEPNHARD BEAQHAUS ATTORNEYS B. BERGHAUS Oct. 3, 1967 METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES 4 Sheets-Sheet 4 Filed Nov. 27, 1961 INVENTOR BEAM/HARD BERG/MUS BY flew fl/m ATTORNEYS United States Patent Ofiice 3,345,280 METHOD AND APPARATUS FOR CONTROLLING GLOW DISCHARGE PROCESSES Bernhard Berghaus, Zurich, Switzerland, assiguor to IONON G.m.b.H., Cologne, Germany Filed Nov. 27, 1961, Ser. No. 155,210 Claims priority, application Germany, Nov. 28, 1960, J 19,075

13 Claims. (Cl. 204-164) The invention is concerned with a process for the carrying out of many chemical processes in a glow discharge and in particular for the carrying out of processes, the efiiciency of which depends in large part on temperature and pressure and the energy in the glow discharge initiating the process, and having optimum efiiciency under certain energy conditions.

It is well known that the practicability of a chemical reaction depends substantially on surrounding or ambient conditions such as temperature, pressure and other energy conditions. Certain chemical reactions can only be carried out at very accurately defined temperatures under accurately determined pressure conditions; otherwise un-' desirable eifects occur.

Naturally this is valid for chemical processes which are carried out under the action of a glow discharge. The known procedures for carrying out chemical processes in glow discharges can be divided into two sharply defined groups from the point of view of the energy conditions prevailing in the discharge.

As is known, the space between the cross-over of the Crooks dark space and the negative glow light, and the upper surface of the cathode is known as fall space thickness. In this region from the upper surface of the cathode to the cross-over place of the Crooks dark space and the negative glow light, the potential rises very rapidly. This rapid rise in potential is known as the cathode fall. Such terminology is fully described in Fundamental Processes of Electrical Discharge in Gases, by L. B. Loeb, published by John Wiley & Sons, Inc., New York, 1947; chapter 6 describes the above terminology.

In a small group the chemical process is carried out in the zone of the cathode fall or the so-called negative glimmer occurring adjacent the cathode of the discharge vessel. The occurrence of a positive column is thereby generally avoided by a suitable arrangement of the electrodes.

However, inasmuch as the cathode fall has a certain minimum level below which it cannot fall and still maintain a glow discharge, depending upon the kind of gas used in the process and the pressure prevailing in the discharge vessel, and is limited to a relatively short discharge distance, relatively high field intensities exist in the Zone of the cathode fall. With such high concentrations of energy some chemical process can be carried out with good results in the zone of the cathode fall in only a few exceptional cases, in which the concentrations of energy favourable for these processes are still higher than the high concentrations of energy mentioned in the cathode fall, or at least only fall below these to a minor degree.

However, favourable concentrations of energy for good results are generally substantially lower with most chemical processes initiated by a glow discharge.

For this reason chemical processes in glow discharges are mainly carried out in the positive column characterized by a substantially small mean energy of the charge carriers, which results in the numerically preponderant known processes in this second group. However, since the positive column consists of a practically electrically neutral plasma of gas ions and electrons and the voltage drop over the positive column is caused principally by wall effects, the field intensity in the zone of the positive 3,345,280 Patented Oct. 3, 1967 column is such that the mean concentration of energy in the positive column lies substantially below the favourable concentration of energy required to achieve good results for most chemical processes initiated by a glow discharge.

That any reaction at all can be achieved with this low concentration of energy can be attributed to the fact that the energy of the individual charged particle (energy carrier) according to the Maxwell distribution is distributed about a mean value corresponding to the energy concentration mentioned, so that a certain part of the energy carrier also has the necessary higher energy to sustain the reaction. However, since this part is only relatively slight, the degree of efiiciency of all chemical processes carried out in the normal positive column is only very slight.

Nevertheless, the carrying out of chemical processes in the positive columns oifers the advantage that the gases participating in the process, once brought to reaction, most likely are not decomposed by carriers of higher energy; whereas, contrary to this, in the negative glow discharge light, in which a part of the energy carrier has the correct low energy for causing the reaction, the process constituents subjected to reaction are most probably decomposed again by carriers of higher energy, so that the efficiency there is lower.

To achieve a higher degree of efficiency in the carrying out of chemical processes in glow discharge it would appear desirable either to increase the concentration of energy in the positive column or to decrease it in the zone of the negative glow discharge light.

The electrical field intensity in a glow discharge is proportional to the gas pressure. But it is not possible to change the energy of the charged particles within a glow discharge by changing the gas pressure since the mean energy of the charged particles is proportional to the product of the electrical field intensity and the mean free path of the particles; and while the electrical field intensity is proportional to the pressure, the mean free path is reversely proportional to the pressure, so the product of both and therefore the mean energy of charged particles is independent of the pressure.

Irrespective of this, a change in the concentration of energy on the basis of pressure variations, if such be at all possible, would not be desirable inasmuch as two magnitudes, which must be adjustable independently of each other to achieve the optimum reaction conditions, would in each case be in a certain interdependent relationship so that the optimum reaction conditions would not be achieved or only in individual cases in which the interdependent relationship coincided by chance with the necessary two magnitudes for the optimum reaction conditions.

The independence of the energy concentration from the pressure within the discharge vessel is therefore an advantage, particularly when suitable processes to influence the energy concentration are discernible.

In connection with the comments on the pressure dependence of the energy concentration it must be pointed out that, as used in this specification, the term concentration of energy refers to the concentration of energy on the individual energy carriers and not to the concentration of energy in a spatial unit. The latter naturally increases in proportion to the pressure since the number of energy carriers increases in the spatial unit named, in proportion to the pressure.

For the sake of completeness it must be stated in this connection with regard to the state of the art that in a known process for carrying out chemical reactions in a glow discharge, a removal of load from at least one electrode is eifected to prevent power loss and to dissipate as much electrical energy as possible in the reaction space rather than on the electrode and so that a decreasing gas pressure is created with increasing distance from the electrode. This appears in the first place to be inconsistent with the above statements since in the zone of the highest pressure, i.e., the immediate vicinity of the electrode in the above example, the highest concentration of energy per spatial unit must also prevail. However, in this process the drop in potential adjacent an electrode, that is the cathode fall, is opposed by such a high drop in pressure that the energy carrier has large masses of ions sucked off from the cathode and thereby the cathode is at least partially relieved of ion bombardment. The above described process is not the process of the present invention, since the object of the present process is to achieve a change in the energy concentration either in the positive column or in the zone of the negative glow-discharge light and, as stated, cannot be achieved through pressure changes. The minimum value of energy concentration in the negative discharge glow light, dependent upon the minimum height of the cathode drop mentioned, cannot fall below the minimum value of the cathode fall because of the independence of pressure, so that of the given possibilities already mentioned-either a weakening of the energy concentration prevailing in the negative glOW discharge light or increase of the energy concentration in the positive column-only the latter is of concern here.

The problem upon which the invention is based is first, to find a procedure for increasing the energy concentration in the positive column of a glow discharge and in the second, to achieve a variability of this energy concentration for the purpose of adapting the process to prescribed optimum energy conditions for a desired reaction.

In accordance with the invention this problem with regard to methods for the carrying out chemical processes in the positive column of a glow discharge is solved. With the lowering of the work function of the electrons from the cathode, occurring with current values above the current necessary to completely cover the cathode, and the consequent increase of the percentage of the electron current density in the entire current density is prevented or at least reduced. Thus an increase in the value of the cathode fall dependent on the electron current density is avoided or correspondingly restricted, also, a potential on the discharge stretch is applied of such an amount that only a fraction of the same drops above the cathode fall. The distance betwen the electrodes is so chosen that with the applied voltage a field density exists above the positive column which is greater than that above an electrically neutral plasma of gas ions and electrons (normal positive column), so that an increase in the energy concentration results in the positive column.

The automatic lowering of the work function of the electrons from the cathode can be prevented to such an extent that the work function for current values above the current necessary for the complete coverage of the cathode are maintained approximately constant with the Work function for incomplete coverage of the cathode, so

that the amount of cathode fall remains approximately the same and constant.

Preferably the automatic lowering of the work function of the electrons from the cathode is prevented or at least substantially reduced through heat dissipation from the cathode. The quantity of heat dissipated per unit of time for the achievement of a controllable value of the cathode fall can also result in a controllable energy concentration in the positive column. The heat dissipation is preferably effected by means of a circulating coolant fed from outside. The variability of the amount of heat dissipated per unit of time can thereby be achieved through variation of the temperature of the cooling agent.

With this process it is preferable that the pressure in the discharge vessel be adjusted to optimum pressure, within the framework of the given possibilities for the maintenance of a glow discharge, for the achievement of the maximum efliciency of the reaction to be carried out.

Furthermore, it can be of considerable advantage if that part of the discharge vessel in which the positive column develops is kept at an optimum temperature for the achievement of a maximum efficiency of the chemical reaction to be carried out. The maintenance of the optimum temperature is preferably effected by means of a current of liquid of the desired temperature flowing around the dis charge vessel or parts of the same.

A particularly advantageous device for the carrying out of the process in accordance with the present invention is an arrangement and a formation of the electrodes and that of part of the discharge vessel limiting the positive column, so that the flow path of a gas current introduced on the anode passes only through the positive column and contact of the gas current with the zone of the negative glow-discharge light or the cathode fall is avoided to the greatest possible extent. Preferably such a device can be so designed that a discharge tube limiting the positive column at the end opposite the anode has a circular cathode. arranged on it with a relatively large interior diameter compared with the diameter of the discharge tube diameter, so that the negative glow discharge light is distributed annularly about the aperture of the discharge tube. In this respect it is particularly advantageous that with such a design the discharge tube at the end opposite the anode is provided with an inverted rim, that the annular cathode is arranged in staggered relationship around this rim against the aperture of the discharge tube in the direction of the anode, and that the limited space through the inner wall of the inverted rim and the outer wall of the discharge tube has some atmospheric pressure owing to connection with the atmospheric space. In this respect it is preferable that the cathode is so staggered against the aperture of the discharge tube that the annular zone of negative glow discharge occurring in front of the cathode does not in its longitudinal range reach as far as the aperture of the discharge tube. With such a device it is also advantageous to arrange a guide tube, preferably with a cone-shaped mouthpiece a short distance ahead of the aperture of the discharge tube, for the further conduction of the gas flowing out of the discharge vessel.

The invention and its theoretical basis are explained in greater detail by the following figures. As follows:

FIG. 1(a). A characteristic current-potential curve of a known glow discharge.

FIG. 1(b). The current dependence of the ions and electron flow density with this known glow discharge.

FIG. 1(a). The current dependence of the percentage shares of the ions and electron flow density in the entire current density.

FIG. 2. The dependence of the potential U lying above the cathode fall on the ratio of the electron flow density to the ion density G,,;/ G,-.

FIG. 3. The characteristic curve of the emission conditions 'y=G /G,- of the electrons released on an average per ion on the cathode with respect to the cathode temperature T FIG. 4. The relation of cathode temperature T on the ion flow density G,- in the form of a system of curves, to the quantity of heat eliminated dw/dt per unit of time as a parameter. 7

FIG. 5(a). The characteristic current-potential curves of a glow discharge by which in accordance with the invention the lowering of the work function of the electrons from the cathode is counteracted, in the form of a system of curves with the counteracting magnitudes, showing in the example the quantity of heat eliminated dw/dt as a parameter.

FIG. 5(b). The current relationship to the entire current density with this glow discharge.

FIG. 5(a). The current relationship to the ion flow density G, in the form of a system of curves with the quantity of heat eliminated dw/dt per unit of time as a parameter.

FIG. 5 (d) The current relationship to the electron flow density G in the form of a system of curves with the quantity of heat eliminated dw/dt per unit of time as a parameter.

FIG. 6. A simplified representation of the principles of the individual phases of the potential distribution U over the discharge range with sudden increase in potential about AU for a known glow discharge.

FIG. 7. A simplified representation of the principles of the individual phases of the potential distribution U over the discharge range with sudden increase in potential about AU for a glow discharge in which the work function of the electrons from the cathode is maintained constant.

FIG. 8. Is a schematic view of a device for carrying out a process in accordance with the persent invention.

In the figures of the drawings, the symbols shown may be defined as follows:

U=voltage I=current G=current density T =absolute temperature of the cathode W=energy (heat energy) t=time dw/dt=heat energy removal per time unit G =density of the total current I G =ion current density G =electron current density U =potential difference over the cathode fa-ll.

With the known glow discharges the characteristic current-potential curve of which is represented in FIG. 1( it is known that in the range of the normal cathode fall, i.e., from current I to I both the potential over the cathode fall and the current density G is constant. The potential thereby corresponds to the minimum amount of the cathode fall which, in order to maintain the self sustaining discharge, may not go below this. With the lowering of the current density from point 0 (FIG. 1(a)) therefore merely the area of the cathode taking part in the discharge contracts, so that the current density Gj remains constant.

In this range of the normal cathode drop the current density with all glow discharges is so low that the cathode practically remains cold.

On the other hand it is known that at the upper limit of the anomalous cathode drop, i.e., at point 2 (FIG. 1(a) the thermal emission of electrons from the cathode begins which then leads to a transition of the glow discharge to an arc discharge.

Consequently in the range of the anomalous cathode fall, i.e., in the range 0 to 2 (FIG. 1(a)), there must result a heating of the cathode which increases with the current. This heating is attributed to the increase of the current density G proportional to the current I occurring in the range of the anomalous cathode fall (FIG. 1 (b) With the known glow discharges, in the field of the anomalous cathode fall with increasing current there is a simultaneous steep increase of the potential U above. the cathode fall, as representedin FIG. 1(a) between the points 0 and 2.

It has been found that this steep increase of the potential U over the current I is attributable to the fact that with increasing current as a consequence of the heating of the cathode, the work function of the electrons from the cathode automatically lowers.

The lowering of the work function of the electrons from the cathode results in more electrons being emitted from the ions impinging on the cathode and, therefore, the ratio of the electron current density to the ion current density G /G increases. The known relation from the principles of thermodynamics applies to this increase and may be expressed as a form of Richardsons equation for self-sustaining discharges, as follows:

wherein G denotes the electron current density, 6 the ion current density, T the cathode temperature and C and C are constants. The principal curve of this function is represented in FIG. 3.

The cathode temperature T results from the heating effect of the ions impinging on the cathode, and therefore increases proportionally to the ion current density G This relation of the cathode temperature T to the ion current density 6 is shown in FIG. 4 in the form of a system of curves with the heat quantity eliminated dw/dt per unit of time as a parameter. Applicant has found that the temperature can be expressed as:

dt UmZ w C4 d 1+- 3 i denote constants and T is the amwhere C and C bient temperature.

An increase in the ratio of the electron current density to the ion current density now involves a proportional increase of the potential U lying above the cathode fall. This increase of the cathode fall results because each electron on the path from the cathode to anode produces a certain number of ions. The ions form a space-charge cloud adjacent the cathode which produces the steep increase of potential before, i.e., the cathode fall. The value of the cathode fall is proportional to the concentration of the ions in the space-charge cloud, i.e., proportional to the charge of this space-charge cloud. If the number of electrons produced from ions discharging on to the cathode from the space-charge cloud is increased and each of these electrons in the space-charge cloud again produces a certain number of ions, then the charge of the spacecharge cloud and thereby the potential U lying above the cathode fall must increase proportionally to the electrons released per ion on the cathode, the so-ca1led release ratio. Since the ratio of the electron current density to the ion current density G /G on the cathode is the same as the release ratio the equation 3 G, (III) therefore results for the potential lying above the cathode fall, whereby C is a proportionality constant. The curve of the function is represented in FIG. 2.

With the Equations I to III and the equation describing the cathode flow in which F is the cathode area, the dependence of the potential U lying above the cathode fall on the cathode flow J for the zone of the anomalous cathode fall can be determined as follows:

Fk(1+ awko. at T Can 05 This somewhat complex formula can be substantially simplified for the potential value I, in which the electron current density G is negligibly small relative to the ion current density, i.e., in the lower range of the anomalous cathode fall, and on the supposition that the heat quantity eliminated is negligibly small. The simplified formula under the suppositions mentioned is then with -exp.

(VII) the magnitude j is thereby the release ratio at the point of the transition from normal anomalous cathode drop and corresponds to the ratio of the electron current density to the ion current density G /G on the cathode which prevails at this point; its magnitude is of the general order of 0.05 to 0.1. U is the potential at this point and in the range of the normal cathode fall above the cathode fall.

It can be recognized from this last equation that the continuous increase in the steepness of the function U (J) in the lower range of the anomalous cathode drop, i.e., j U U declines again with increasing U until finally in the range j U -U a continuous decline of the steepness and finally a maximum of the function is shown. This range characterized by j U U is the range where the electron current density comes into the magnitude of the ion current density or already exceeds the same, i.e., in the terms usual in the literature the range of the thermal emission of electrons from the cathode, which follows the transition into an arc discharge directly, namely after exceeding the above mentioned maximum of the function.

The above Equation VII therefore exactly describes the variations of the potential lying above the cathode fall in the range of the anomalous cathode fall for known glow discharges up to the maximum potential U The Equation V on the other hand applies also in the case where the lowering of the work function of the electrons on the cathode is counteracted.

To counteract the heat produced on the cathode through the impingement of the ions, heat dissipation by suitable means is the obvious method. There are, however, a number of other possibilities to counteract this lowering of the work function. It is possible, for example, to apply braking to the ions before they reach the cathode, by means of electric or magnetic fields. This general method in turn offers a large number of possibilities for carrying this out. An example is the arrangement of a brake grid in front of the cathode, already known in its mode of action from valve techniques, which is held at a negative potential with respect to the cathode. A braking section then occurs between such a brake grid and the cathode, so that the ions strike the cathode with a substantially lower speed and heating of the cathode is thereby counteracted. On the other hand, however, such a brake grid also slows the electrons being emitted from the cathode, so that a double effect is produced. The amount of the brake deacceleration, and indirectly thereby the heating of the cathode, is then controllable by means of the potential placed on the brake grid.

FIG. 5(a) shows a family of curves resulting from the functions U f(]) from the Equation V, represented with the heat quantity eliminated per unit of time dW/dt as the indicated parameter. In the FIGURES 5(b), (0) and (d) are shown the corresponding curves of the entire current density, the ion current density and the electron current density, respectively, with respect to the cathode current I. From a comparison of the curves the relation of the increase of the function U =j(J) to the ratio of the electron current density to the ion current density can be seen. For example, the electron current density G increases relatively quickly with the steepest curve in FIG. 5(a), whilst the ion current density G changes only a little. On the other hand the ion current density 6, with the flattest curve in FIG. 5(a) is almost the same as the entire current density G whilst the electron current density increases only slightly.

With this controllability of the amount of the cathode fall independent of the current J, which results for example through change of the heat quantity eliminated from the cathode per unit of time dw/dt as in FIG. 5(a) with current I a controllability of the energy concentration in the positive column can now be achieved. This will now be explained with reference to FIGS. 6 and 7.

Assume that two glow discharge sections of the same structure and at the same pressure are operated at the transition point from the range of the normal to the range of the anomalous cathode fall. In one of the two glow discharge sections, the distribution of potential, represented by the discharge section in FIGS. 6(a) to 6(d), without heat dissipation from the cathode, and in the other, the potential distribution is represented in FIGS. 7(a) to 7(d) and is operated with such a heat dissipation that the work function of the electrons from the cathode remains constant. In the initial condition, i.e., the transition point from normal to anomalous cathode fall, the distributions of potential represented in FIGS. 6(a) and 7(a) are the same over the two discharge sections. The field density over the positive column is thereby of the same amount as with the known glow discharges with corresponding pressure and temperature conditions and accordingly the potential drop (U- U above the positive column is relatively slight.

If the potential on both discharge sections is now suddently increased by the amount AU, then this increase in potential AU, as represented in FIGS. 6(b) and 7(b), superimposes linearly over the entire discharge section so that the field density at each point of the discharge section increases by the same amount AU/a, where a signifies the electrode interval. Consequently a considerable increase in the field density over the positive column occurs in both cases in the first moment, which leads to a considerable acceleration of the electrons in the direction of the anode and thereby results in a considerable increase in the current. At the same time the field density above the cathode fall is so increased that the energy of the ions striking on the cathode is increased to the same extent.

The increase in energy of the ions, without heat dissipation, results in an increase of the ratio of the electron current density to the ion current density (G /G on the cathode. This increase of G /G,- in turn results in an increase in the potential U which for its part involves an increase of Gel/Gj again as a consequence of the increase of the ion energy and thereby a further heating of the cathode. For this reason the amount of the cathode fall increases continuously in the case of a glow discharge section without heat dissipation, as shown in FIG. 6(a). This continues until the original potential (UU again prevails above the positive column and corresponds to the original field density, as can be seen from FIG. 6(d).

The final condition, FIG. 6(d), is such that the potential increase by AU aifects only the increase of the cathode fall to U =(U -|-AU) whilst no increase in the energy concentration has resulted in the positive column.

In the case of the glow discharge section with which the work function of the electrons from the cathode is kept constant, the increase in energy of the ions cannot result in heating of the cathode, since with the constant work function, a constant temperature of the cathode results. True, the release ratio, i.e., the value G /G at first increases slightly with the increase in the potential above the cathode fall by AU FIG. 7(b), but this increase, which varies generally as the logarithm of the potential U, and therefore results in a substantially smaller percentage increase of G /G,- than the potential percentage increase AU /U is not suflicient to maintain this increase in potential AU of the cathode fall. The potential above the cathode fall therefore lowers, which in turn leads to a corresponding lowering of the G /G,- and thereby to a further sinking of the potential above the cathode fall, as shown in FIG. 7(c). In the final condition the original amount of the cathode fall U is again reached. Consequently, the increase in potential by AU in the glow discharge section with constant work function beneficially affects the increase in potential and, correspondingly, the field density above the positive column. As can be seen from FIG. 7 (d), in the final condition the potential above the positive column is correspondingly the same, equal to [(U-- U H-AU] so that a considerable increase in the energy concentration results in the positive column. This increase in the energy concentration is controllable proportionally to and with AU.

FIG. 8 is a diagrammatic representation of a device for the carrying out of the described process in accordance with the present invention. The special advantage of this device lies in that the gas flow 2 passed to the anode 1 is conducted only by the positive column 3 and does not come into contact with the zone of the negative glow discharge light 5 occurring adjacent the cathode 4. The circular cathode 4 is cooled by a liquid stream 6 and is so oifset from the aperture 7 of the discharge tube 8 in 60 the direction of the anode 1 that the annular zone of glow discharge 5 adjacent the cathode 4 does not extend to the aperture 7 of the discharge tube 8. An inverted rim 9 defining a portion of a jacket is connected to the tube 8 around aperture 7 and the space between jacket 9 and 65 tube 8 is subjected to atmospheric pressure. A casing portion 10 of jacket 9 defines a space through which a liquid stream 11 flows. The stream 11 is kept at the temperature required to maintain the optimum temperature and flows about the entire discharge tube 8, as far as its aperture 70 7 and thereby affects the full length of the positive column 3. In addition, at a slight distance in front of the aperture 7 of the discharge tube, a guide tube 12 having a cone-shaped projection 13 is arranged for the further a receptacle (not shown). The guide tube 12 provides further safety in that the gas flow flowing through the positive column 3 and reacting there does not come into contact with the negative discharge glow light 5.

What I claim is:

1. In a method of controlling the energy in the positive column of a glow discharge in a vessel, the steps of operating said glow discharge at current values above those necessary for the complete coverage of the cathode, minimizing the inherent lowering of the work function of the electrons from the cathode by withdrawing heat therefrom in an amount sufiicient to maintain the work function of the electrons from the cathode substantially constantly the same as the work function with incomplete coverage of the cathode and thereby minimizing the increase of the percentage of the electron current density in the entire current density so that an increase of the cathode fall relative to the electron current density is held to a minimum, controlling the potential applied to the discharge section to such value that only a fraction of the same lies over the cathode fall, and maintaining a distance between the electrodes such that said applied potential produces a field density substantially greater than that over an electrically neutral plasma of gas ions and electrons in the positive column whereby to increase the concentration of energy in the positive column.

2. A method according to claim 1 wherein heat withdrawal is effected by circulating a cooling agent relative to said cathode.

3. A method according to claim 2 wherein the heat quantity withdrawn per unit of time is varied by changing the temperature of the cooling agent.

4. A method according to claim 1 wherein the pressure in the discharge vessel is adjusted to achieve the maximum reaction efl'iciency at the optimum pressure for the selected chemical process to be carried out, within the range of values possible for maintaining a glow dis charge.

5. A method according to claim 1 wherein at least that part of the discharge vessel in which the positive column forms, is maintained at an optimum temperature for the achievement of the maximum efficiency for the selected chemical process to be carried out.

6. A method according to claim 5 wherein the maintenance of the optimum temperature is achieved by means of a circulating current of liquid having this temperature flowing around at least a part of the discharge vessel.

7. A device for controlling the energy in the positive column of a glow discharge vessel having a gas discharge tube defining said positive column having an anode at one end and the other end open, an annular cathode with a large internal diameter relative to the diameter of the discharge tube and arranged adjacent the open end of said discharge tube opposite the anode, so that the negative glow discharge light is distributed annularly about the end of the discharge tube, means for directing gas to flow through said positive column so that contact thereof with the zone of the negative glow discharge light and the cathode fall is minimized, and means to withdraw heat from the cathode.

8. A device according to claim 7 wherein said discharge tube at said end opposite the anode, is provided with an inverted rim spaced therefrom, said annular cathode being arranged about this rim adjacent the open end of the discharge tube and olfset therefrom in the direction of the anode, the space between said inverted rim and the outer Wall of the discharge tube being subjected to atmospheric pressure.

9. A device according to claim 8 characterized in that the cathode is so far offset from said discharge tube that the annular zone of negative gas discharge light adjacent said cathode does not extend longitudinally as far as the open end of the discharge tube.

10. A device according to claim 7 characterized in that conduction of gases flowing from the discharge tube 8 into there is a guide tube aligned with and slightly spaced from 1 1 the open end of said discharge tube for the conduction of gas flowing from said discharge tube.

11. A device according to claim 10 characterized in that the guide tube has a cone-shaped open end forcing the open end of said discharge tube.

12. A device according to claim 7 characterized in that the discharge tube is provided with a surrounding jacket through which a stream of coolant liquid flows to maintain the tube at a desired temperature.

13. A device according to claim 12 characterized in that said jacket comprises an extension of inverted rim, the space between said inverted rim and the outer wall of the discharge vessel being in communication with the interior of said jacket whereby said coolant liquid flows therethrough.

References Cited UNITED STATES PATENTS 2,550,089 4/1951 Schlesman 313-231 X 2,849,356 8/1958 Manion 204177 2,849,357 8/1958 Devins et al. 204177 3,004,133 10/1961 Berghaus et al.

3,005,762 10/ 1961 Penn 204164 3,185,638 5/1965 Cremer et al 2043 12 1O HOWARD S. WILLIAMS, Primary Examiner.

GEORGE N. WESTBY, WINSTON A. DOUGLAS,

JOHN H. MACK, Examiners.

15 D. E. SRAGOW, Assistant Examiner.

Claims

1. IN A METHOD OF CONTROLLING THE ENERGY IN THE POSITIVE COLUMN OF A GLOW DISCHARGE IN A VESSEL, THE STEPS OF OPERATING SAID GLOW DISCHARGE AT CURRENT VALUES ABOVE THOSE NECESSARY FOR THE COMPLETE COVERAGE OF THE CATHODE, MINIMIZING THE INHERENT LOWERING OF THE WORK FUNCTION OF THE ELECTRONS FROM THE CATHODE BY WITHDRAWING HEAT THEREFROM IN AN AMOUNT SUFFICIENT TO MAINTAIN THE WORK FUNCTION OF THE ELECTRONS FROM THE CATHODE SUBSANTIALLY CONSTANTLY THE SAME AS THE WORK FUNCTION WITH INCOMPLETE COVERAGE OF THE CATHODE AND THEREBY MINIMIZING THE INCREASE OF THE PERCENTAGE OF THE ELECTRON CURRENT DENSITY IN THE ENTIRE CURRENT DENSITY SO THAT AN INCREASE OF THE CATHODE FALL RELATIVE TO THE ELECRON CURRENT DENSITY IS HELD TO A MINIMUM, CONTROLLING THE POTENTIAL APPLIED TO THE DISCHARGE SECTION TO SUCH VALUE THAT ONLY A FRACTION OF THE SAME LIES OVER THE CATHODE FALL, AND MAINTAINING A DISTANCE BETWEEN THE ELECTRODES SUCH THAT SAID APPLIED POTENTIAL PRODUCES A FIELD DENSITY SUBSTANTIALLY GREATER THAN THAT OVER AN ELECTRICALLY NEUTRAL PLASMA OF GAS IONS AND ELECTRONS IN THE POSITIVE COLUMN WHEREBY TO INCREASE THE CONCENRATION OF ENERGY IN THE POSITIVE COLUMN.