US2697793A - Induction-conduction charging of electrostatic generators - Google Patents

Description

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J. G. TRUMP ET AL INDUCTION-CONDUCTION CHARGING OF ELECTROSTATIC GENERATORS Filed Dec.

Dec. 21, 1954 United States Patent INDUCTIQN-CONDUCTION CHARGING OF ELECTROSTATIC GENERATORS John G. Trump, Winchester, and Robert W. Cloud, Lexington, Mass., assignors to Research Corporation, New York, N. Y., a corporation of New York Application December 12, 1951, Serial No. 261,244

17 Claims. (Cl. 310-5) This invention relates to high potential electrostatic apparatus embodying the general principles disclosed in the U. S. patent to Robert J. Van de Graaff, No. 1,991,236, in the U. S. patent to John G. Trump, No. 2,252,668, and in the U. S. patent to John G. Trump and Robert W. Cloud, No. 2,503,224, and also relates to a new method and system pertaining thereto, and particularly to the transfer of electric charge to and froma charge conveyor, and more particularly it relates to the transfer of electric charges to and from an endless charge-carrying conveyor, and especially to the transfer of electric charges to and from an endless belt or belts as used in the Van de Graaff type of electrostatic generators and accelerators.

In order that the principle of the invention may be readily understood, we will first sufliciently describe the present corona method of charge transference, and state the limitations thereof which led to the present invention, and we will set forth the relative advantages of the latter, and we will then disclose, as examples, several embodiments of apparatus by each of which the method of our present invention may be practiced, and constituting a type of the system of our invention.

Present corona method of charge transference Van de Graalf electrostatic high voltage sources consist of a well-insulated high voltage terminal and an insulating belt which transfers electric charge between this terminal and ground. Electric charge is deposited upon this insulating belt or removed from it by causing ionization of the gaseous medium at the region where this deposition or removal is to take place. This is commonly done by presenting toward the belt an array of points or the edge of a screen or a thin metal sheet. For example, negative electric charge is deposited upon the insulating belt by maintaining a potential difference between the pulley over which the belt passes and a row of sharp points which are directed toward the pulley from the other side ofthe belt. A negative potential applied to the points results in a high electric field which causes the ionization of the gas by the Townsend alpha process and results in the deposition of negative electric charge upon the intervening insulating surface of the belt.

This corona method of transferring electric charge to a moving insulating belt surface has become the conventional method for modern Van de Graaff accelerators. First applied to electrostatic high voltagesources which operate in air at atmospheric pressure, the corona method is now also the universal method of charge transfer in modern electrostatic generators insulated in compressed gases. It has been used in apparatus insulated by gas at pressures of 400 lbs. per square inch and higher.

There are certain disadvantages in the said present corona method of charge transference, which we will briefly state as follows:

1. The creation of ionization for the deposition or removal of electric charge from an insulating belt becomes increasingly difiicult with increased gas pressure.

2. Higher voltages are required to produce the necessary ionization of the gaseous medium the better the dielectric strength of the gas.

3. A peculiar phenomena known as the positive pointto-plane effect introduces special difliculties in spraying positive charge upon an insulating surface when the gas pressure is above a certain critical value.

4. Ionization results in the dissociation of gas molecules and increases their chemical activity with resultant tendtric field which induces the flow 2,697,793 Patented Dec. 21, 1954 ency to cause deterioration of the insulating belt material and of the gas itself, as well as corrosion of metal surfaces.

5. The corona charge-transferring mechanism is extremely sensitive to the nature of the gas, to the gas pressure, to the geometric relationship of the points and the belt, to the sharpness of the points and edges, and to other factors ditiicult to control.

6. Fundamentally the corona mechanism as a means of transferring an electric charge is undesirable because it imposes upon the gaseous insulating medium surrounding the high voltage source the conflicting requirements that it be capable both of readily conducting electricity at the charge-transfer regions and of insulating high voltages and gradients without ionization in other regions.

The present invention The present invention, involving method, system and apparatus, eliminates the necessity of gaseous ionization, in transferring electric charge to and from the belt of Van de Graatf electrostatic generators and accelerators, and while we will herein illustrate and describe a charge conveyor of the endless belt type, it is to be understood that our charge conveyor may be any suitable moving structure, preferably of the endless type, such as a traveling belt or a large, rapidly rotating disk.

In accordance with our invention, and referring to the herein disclosed several different embodiments of beltconveyor apparatus for practicing the same, we, in one way or manner of carrying out our novel method, use a novel, semi-conducting endless belt and electrostatically induce charge to flow onto such belt from a metal charging member with which it is momentarily in contact, such as the lower pulley by which the belt is driven. The elec-' of electric charge onto such belt extends beyond the pulley to a region where the belt has lost conductive contact with the said metal charging member, namely, the lower pulley. The resistivity of the belt is, as hereinafter fully disclosed, such that once such conductive contact has been lost, the charge remains bound upon the belt without essential loss until it is removed at some subsequent state in the generator process, as will be fully described.

In the accompanying figures of the drawings we have, as examples, disclosed several different embodiments of belt conveyor means for the practice of our invention.

Fig. 1 represents in vertical transverse section, the lower part only of an electrostatic generator of the general type disclosed in the said patent to Trump, No. 2,252,668, and in the said patent to Trump and Cloud, No. 2,503,224, but having our invention incorporated therein and disclosing how a negative electric charge is induced to flow on the ascending run of the belt, by maintaining a positive poterfiial on the inducing plate, with respect to the ground P y;

Fig. 2 is a similar view of the upper part only, of such electrostatic generator, and it discloses how the electric charge is removed from the ascending run of the belt by means of a conductive contact, as by contact with the upper pulley of the generator, or by contact with a small pulley within the electrode terminal;

Fig. 3 is a diagrammatic View of a small lengthwise extending portion of the belt from edge to edge thereof, wherein the semi-conducting material is applied to the inner surface of the belt as a coating or layer, on isolated areas having the form of spaced lines extending transversely of said belt;

Fig. 4 is a similar diagrammatic view, but representing the isolated areas as a great multiplicity of dots; and

Fig. 5 is a similar diagrammatic view, but representing the isolated areas as having the form of spaced circular generator has the main high hemispherical shape and free from external projections. In practice the saidrelectrode 1, also referred to as the terminal, is supported in any suitable manner, as, for example, in the manner shown in Fig. 1 of the said U. S. patent to Trump, No. 2,252,668. The bases of the supporting pillars or columns rest on a base plate of conductive material supported by brackets or otherwise attached to the inner walls of a surrounding tank 1a, which is or may be such as is shown at 21 in said patent to Trump, andwhich is filled with gas, which in the practice of our invention may be assumed to be air, or preferably a mixture of nitrogen and carbon dioxide, maintained under a suitable pressure as, for example, between 200 and 400 or more pounds per square inch above atmospheric.

The charge carrier, to the novel nature of which our invention is mainly directed, is here, for example only, shown as in the form of an endless belt indicated generally at 2, and of a construction herein subsequently de scribed, and whereon the charges are carried upon its surface. At its lower end the belt passes about a metallic driving pulley 3, which therefore has a conductive surface. Such driving pulley 3 is journalled in suitable brackets on the base plate, so that the said pulley 3 has a grounded connection. In practice this lower pulley is insulated and connected to ground through a microammeter I, this being a convenient way of measuring the current transferred to the belt from the lower pulley. The said pulley is driven, preferably, by an electric motor to which current is supplied by conductors entering the walls of the tank through a suitable bushing.

The said belt 2 runs vertically upward and then downward in a parallel run or series of runs, depending upon the number of the belts used, passing into and out of the hollow electrode or terminal 1, and over a metallic pulley or pulleys 4, within said electrode 1, and which therefore has a conductive surface similar to that of the metallic driving pulley 3. The said pulley 4 is journalled in but is insulated from brackets supported by the ring referred IO.

As will be more fully described, at the lower end of the said belt 2, charges of one sign are established on the said moving belt, and at its upper end the charges carried thereby are removed and transferred to the hollow electrode or terminal 1. If the upper inductor is maintained at a negative potential with respect to the pulley which is connected to the terminal, then, simultaneously, charges of opposite sign are transferred from the electrode or terminal 1 to the belt 2 at its upper end and are carried by the descending run to the lower end, where they are removed.

In Fig. 1 the pulley 3 is shown as connected to ground at 4a, and the inductor or inducting plate 5 is shown as connected at 4b to an electromagnetic source of charge supply, conventionally indicated, but which may comprise a source of rectified alternating current utilizing a transformer and a vacuum tube rectifier.

In both Figs. 1 and 2 are represented at 40 columns of equipotential planes as a means for controlling the field due to the belt charge. These planes are separated one from the other by solid insulators, such as glass or porcelain, and they are held at the proper potential by allowing a small current to flow along the columns through resistors connected between the planes. Each equipotential plane contains a series of conductors extending transversely across the entire width of each run of the belt 2 and on each side thereof, each separated from the belt 2 by a relatively small distance.

In the embodiment of the apparatus of our invention shown in Figs. 1 and 2, a negative electric charge is induced to flow on the ascending run of the belt 2, by maintaining a positive potential on a lower inducing or inductor plate 5 closely spaced with respect to the outer surface of said belt 2, and shown as curved so as to be in substantial parallelism with the belt 2 in the region where it is in contact with the lower pulley and for some distance beyond on the departing side. At the upper pulley 4, shown in Fig. 2, we provide a similar inducing or inductor plate 6 also closely spaced with respect to the outer surface of the belt 2, and similarly curved, so as to be in substantial parallelism with the adjacent portion ofthe belt in the region of pulley contact and for some distance beyond as shown. At said upper pulley 4, if the inductor plate 6 and the pulley 4 are at the same potential, then the charge flows from the belt 2 to the pulley 4, when they become conductively connected.

The flow to the pulley 4 is due to the electric field of the charge which exists on the belt 2.

Fig. 2 shows the manner in which electric charge may be removed from the ascending run of the belt 2 by means of a conductive contact (such as the small pulley) within the electrode or terminal 1. The charge so removed is conducted to the upper inducing or inductor plate 6 and thence to the high voltage electrode or terminal 1 through the resistance R. The IR drop in the resistance R supplies the electric field between the upper inducing or inductor plate 6 and the upper pulley 4, which is directly connected to the terminal, to cause electric charge of the opposite sign to flow conductively from the pulley 4 onto the surface of the descending run of the belt 2.

In the inductive conductive charging system herein disclosed and claimed, it is not necessary that the entire belt be of a semi-conducting character. We prefer to use a belt which is essentially insulating except for a relatively thin semi-conducting sheath on its inner surface. This appears to have the advantage that the semi-conducting sheath can be made of relatively lower resistivity material for a given leakage of electric charge along the belt under the impetus of the voltage of the generator.

Such a semi-conducting sheath applied to the inner surface of the belt 2 is indicated at 7 in both Figs. 1 and 2. It may extend over the entire inner surface of the said belt 2 and that is the construction indicated in Figs. 1 and 2.

Alternatively, we have produced a suitable semi-conducting belt by introducing the semi-conducting material on isolated areas of an insulating belt structure. These isolated areas may be of different form. In Fig. 3 they have the form of broken, spaced lines 8 extending transversely of the belt from substantially edge to edge. In- Fig. 5 they have the form of circular areas 9, preferably symmetrically arranged in parallel transverse rows, extending substantially from edge to edge of the belt 2, and in Fig. 4 they take the form of a great multiplicity. of dots 10 extending preferably from edge to edge of the belt 2.

Our invention, in accordance with which the charge conveyor, desirably of an endless character, and is here shown as an endless belt 2, but which as stated in the preliminary description herein may be a large, rapidly rotating disk, has a semi-conductive inner surface. It is radically distinguished from an insulating belt carrying conductive elements. The latter type of belt is not new in the art, it having been suggested in the Van de Graafi Patent No. 1,991,236, but there repudiated, as shown by the following quotation from lines to 62 of page 4 of the specification of said patent as follows:

The use of conducting spots or zones on a belt or disk type of charge carrier operating in air is, contrary to the prior practice, to be avoided as it results in decreased efficiency due to the lessened effective surface for transferring charges and may materially reduce the maximum voltage that may be established on the electrode or terminal. This will be apparent since a conducting spot or zone on the charge carrier forms, at the instant that it enters the slot in the wall of the electrode, a relatively sharp edged extension of the electrode, thus promoting a corona or leakage discharge from the electrode.

A conductor-carrying belt has the limitation that the conductive elements are usually metals of exceedingly high conductivity and must be spaced relative to one another along the surface of the insulating and supporting belt structure in order that the charge may remain isolated on the conductive elements and that a high voltage may be insulated along the belt length. While such conductorcarrying belts may be built both in principle and in fact, they would possess inherent disadvantages because of the physical inhomogeneity of the composite belt, the natural reduction in its voltage insulating ability, the presence of sharp edges on the conductive elements and the impossibility of utilizing the entire belt surface for charge carrying purposes.

-In contrast to this, a belt constructed in accordance with our invention of the proper semi-conducting material may use its entire surface for the deposition and transfer of electric charge. It has structural homogeneity; it is comparatively free from the high electric fields associated with metallic conductive elements, and it is inherently capable of insulating higher voltages in the same overall length. The use of semi-conducting material in this manner is new in the art and. special techniques must be used to obtain such conductivity as to permit the conductive transfer of charge to' the belt under the action of an inducingfield and yet allow this charge to remain fixed to the belt surface during its passage toward the electrode system on which this charge will be stored.

We have found that the resistivity of this semi-conducting material must lie in the range from ohm cm. to 10 ohm cm., depending upon such factors as the desired charge density, the available voltage gradient, the speed of; the belt and pulley size, and the intimacy of contact betweenbelt and charge source. This range of resistivity is in marked contrast to that which is conventionally used in' the ionization methods of charge transfer. Therein the belt resistivity is commonly of the order of 10 to 10 ohmcm. and rarely less than 10 Our semi-conductin g'belts' may be used with conventional charging systems The semi conducting belts herein disclosed can be used in Van de Graaff voltage sources which utilize the ionization method of charge deposition and removal from the belt surface. By directing a row of points toward a metal pulley and applying an appropriate potential between them, electric charges of the polarity characteristic of the pointed system will be directed toward the intervening belt and deposited upon it. This is true whether the belt be of the conventional insulating nature or one which possesses a semi-conducting surface of the general characteristics that we have herein described. The semiconducting belt may possess an advantage in that the charge would tend to distribute itself more uniformly over the available belt surface and since unwanted surface charges produced by friction would be minimized.

Effects of induction conduction charging The novel, herein disclosed method of electrically charging the charge conveying belt system of the Van de Graalf accelerators has the following effects:

1. It eliminates ionization of the gaseous medium with its resulting energy loss, dissociation of the gas molecules, deterioration of the belt material and corrosion of metal surfaces.

2. It is free of the polarity effects of the ionization method which generally made it more difficult to deposit positive charge upon belt surfaces at the higher gas pressures.

3; It permits unrestricted use of superior gaseous dielectrics as the essential insulating medium for Van de Graaff accelerators. Such superior dielectrics include the electronegative gases such as Freon (CCl2F2) and sulfurhexafiuoride (SP6).

4. It is largely free of the unsteadiness of charge transfer which was due to difficulties in maintenance of sharp points and screen edges and their spacing relative to the belt and pulley.

5. The charge transferred by our herein disclosed, novel method is independent of the nature of the gas and is directly proportional to the inducing potential Y.

6. Higher charge densities can be carried by the semiconducting belt system because the electric charge can be more uniformly distributed over the belt surface.

7. The voltage insulating strength of the belt may be increased because the charge is more uniformly applied and the belt is free of the condition of ionization at its grounded and high potential ends.

Without limiting ourselves thereto, as the materials any one of which we can apply to the inner surface of the belt 2 orother semi-conducting charge conveyor as the layer or coating 7, 8, 9 or 10, we state that a semi-conducting material suitable for the purposes of this invention can be made of a rubber compound using neoprene rubber and tricr'esyl phosphate as a plasticizer which further increases the conductivity of neoprene. A temporarily satisfactory method of rendering the inner surface of the insulating belt or charge carrier of the proper degree of semi-conductivity is by coating it with Carbowax, which is polyethylene glycol. Other forms of rubber may be used, such as Hycar, which already possesses a considerable conductivity in comparison with natural rubber, but requires the further inclusion of some material" to bring resistivity down to the range of 10 ohm cm. to 10 o hm'cm. In principle it would be possible to add carboncontaining materials to rubber in order to secure the desired degree of conductivity.

The semi-conducting material may be distributed uniformly over the inner belt surface, or as shown in Figs. 3, 4 or 5. Then again, the semi-conducting surface may be made of a material which extends well into the volume of the belt. Within the invention the semi-conducting coating may be characteristic of the semi-conducting nature of the entire belt structure. In any case, the semiconducting belt 2 permits the flow of electric charge to and from the belt 2 surface, but resists to an almost complete extent the flow of electric charge lengthwise the said belt 2.

The lower and upper inducting or inductor plates 5, 6, are preferably made of metal such as aluminum, steelor brass.

It will be evident from the foregoing description that in accordance with our invention, electric charge is deposited upon the belt or other moving charge conveyor by providing a semi-conducting layer on the inner surface of the belt or other conveyor, and electrostatically inducing charge to flow between the conductive surface of a pulley or the like and the semi-conductive surface of the belt or other moving charge conveyor, during the interval they are in contact. The charge flows to the belt or other moving charge conveyor from the conducting pulley (in the case of a belt) or from its substitute or equivalent, if some other form of charge conveyor is employed. The charge is similarly conveyed from the belt.

Each of the inductor or inducting plates 5 and 6 is closely spaced with respect to the belt 2 and produces an electric field between such belt and the respective conductive pulleys 3 and 4. g p

The belt 2, constructed as herein described, is capable of insulating high electric gradients along its length, and it has a semi-conducting surface layer, desirably of resistivity 10 to 10 ohm cm. In one embodiment such inner surface layer may be composed of such material that its resistivity is lowered to a value in the range below 10 ohm cm. by an increase in its temperature, during the interval it is in contact with a heated pulley such as 3 and 4', and its resistivity increases during the interval it is' not in contact with the pulleys.

It will be evident from the foregoing description that we have provided high voltage apparatus and system consisting of a metallic terminal insulated and supported from ground, a rapidly moving belt passing between ground and a region with such terminal, an inductor plate closely spaced to the said belt and producing an electric field between the said belt and the metal, conductive pulley at the grounded end of the system, the said belt being coated preferably in the manner and to the extent described with a materialof such semi-conducting nature that electric charge can flow from said pulley to said belt, and can also flow from said belt to a conductive pulley within the terminal, there being an inductor or inducing plate closely spaced with respect to said conductive pulley within the terminal.

It is further to be understood that the semi-conducting layer is of such innate conductivity as to permit the acquisition during the interval of contact with the respective pulleys, of a surface charge density approaching the maximum that can be insulated in the gaseous medium within the tank that surrounds the described parts, such as that illustrated at 21 in Fig. l of the U. S. patent to Trump No. 2,252,668, or illustrated at 4 inFig. l of the patent to Trump and Cloud No. 2,503,224.

Our invention includes, and we hereby specifically make disclosure of a plurality of insulating belts passing at high linear velocity between ground and an electrode terminal, each of said belts being coated on their surfaces, and specifically upon their inner surfaces with a semi-conducting material.

Having thus disclosed one embodiment of the apparatus of our invention, and by means of which the system and method of our invention may be practiced, we desire it to be understood that although specific terms are employed, they are used in a generic and descriptive sense, and not for purposes of limitation, the scope of the invention being set forth in the following claims.

We claim:

1. Induction-conduction charging means in a high potential electrostatic apparatus including a chamber or tank containing gas under high pressure comprising a metallic or other conductive surface, and a moving charge conveyor having at least one semi-conductive surface, and means electrostatically to induce electric charge to a surface and such moving charge conveyor.

flow Without gaseous ionization between such conductive 2. Induction-conduction charging means in a high potential electrostatic apparatus including a chamber or tank containing gas under high pressure comprising a rapidly moving charge-carrying belt having a semi-conductive inner surface, a metallic or other conductive surface in contact with said belt, and means electrostatically to induce electric charge to flow without gaseous ionizaation between such conductive surface and the semi-conductive surface of such charge-carrying belt during the interval of contact.

3gInduction-conduction charging means in a high potential electrostatic apparatus including a chamber or tank containing gas under high pressure, comprising a metallic terminal insulated and supported from ground, a moving, charge-conveyor belt having as an essential element a semi-conducting surface and passing from a region at ground potential to a region within such metallic terminal, and electrostatic induction means for transferring charge from ground to said belt and from said belt to said terminal without gaseous ionization, there being a conducting pulley with which said chargeconveyor belt is in contact, said belt being provided upon its surface with a semi-conducting layer to or from which charge flows during the interval such belt and pulley are in contact.

4. That-system of transferring electric charge in a high potential electrostatic apparatus and thereby eliminating the necessity of gaseous ionization in transferring electric charge to and from the moving charge conveyor thereof wherein there is provided an endless traveling conveyor having a semi-conducting surface, and wherein there is provided a metallic or other conductive surface, and wherein means is provided for electrostatically inducing electric charge to flow without gaseous ionization between such metallic or other conductive surface and the semi-conducting surface of said endless traveling conveyor.

' 5. Induction-conduction charging in a high potential electrostatic apparatus and thereby eliminating the necessity of gaseous ionization in transferringelectric charge to and from themoving charge conveyor thereof, comprising a rapidly moving charge-carrying belt having semi-conducting ,material distributed in lines extending transverse to the direction of motion of such belt, upon the inner surface thereof, a conductive pulley about which said belt passes, and means electrostatically to induce electric charge to flow between such'pulleyand such inner surface of said belt.

6. Induction-conduction charging in a high potential electrostatic apparatus, and thereby eliminating the necessity of gaseousionization in transferring electric charge to and from the moving charge conveyor thereof, comprising a rapidly moving charge-carrying belt having semi-conducting material distributed in the form of small spaced areas on the inner surface of such belt, a conductive pulley about which said belt passes, and means electrostatically to induce electric charge to flow between such pulley and such inner surface of said belt.

7. High-voltage charging in a high potential electrostatic apparatus, and thereby eliminating the necessity of gaseous ionization in transferring electric charge to and from the moving charge conveyor thereof, consisting of a well-insulated metal terminal from ground, a rapidlymoving belt, a conductive pulley in the region of ground potential, and a conductive pulley within said terminal and about both of which said belt passes, inductor plates closely spaced to said belt and in the operation of the apparatus producing electric fields between said belt and the said pulleys, the said belt having a coating of a material of such a semi-conducting nature that electric charge can flow between said pulleys and said belt.

8. High-voltage apparatus consisting of a metallic terminal insulated and supported from ground, a rapidly moving belt passing between ground and a region within said terminal, said belt having an inner surface layer of such material that its resistivity is lowered to a value in the range below 10 ohm cm. during the interval that it is in contact with a heated pulley about which it passes and a chamber or tank to contain gas under pressure and within which the said apparatus is located.

9. High voltage apparatus consisting of a well-round ed metallic terminal insulated in a gaseous medium from ground, acolumn of alternatelyarranged insulating and.

conducting members for the physical support of said terminal,'ametallic or other conductive pulley within said terminal, a metallic or other conductive pulley in a region near ground potential, an endless'belt of insulating material passing over said pulleys, the said belt being coated on its inner surface with a layer of semi-conductive material, two inductor plates, respectively closely spaced to said belt at each of said pulleys, means to establish an electric field between said inductor plates respectively and said pulleys so as to cause the flow of electric charge between said pulleys and the semi-conducting layercoating on said belt, the said semi-conducting layer being of such innate conductivity as to permit the acquisition during the interval of contact with said pulleys, of a surface charge density approaching the maximum that can be insulated in said gaseous medium.

l0. High-voltage apparatus consisting of a well-rounded metallic terminal insulated in a gaseous medium from ground, a column of alternately arranged insulating and conducting members for the physical support of said terminal, a metallic or other conductive pulley within said terminal, a metallic or other conductive pulley in a region near ground potential, an endless belt of insulating material passing over said pulleys, the said belt being coated on its inner surface with a layer of semiconductive material, two inductor plates respectively closely spaced to each belt at each of said pulleys, means to establish an electric field between said inductor plates respectively and said pulleys, so as to cause the flow of electric charge between said pulleys and the semi-conducting layer coating on said belt, the said layer of semiconductive material having a resistivity of 10 to 10 ohm cm.

11. High voltage apparatus consisting of a metallic terminal insulated in a gaseous medium from ground, insulating means for the physical support of said ter minal, a conductive pulley within said terminal, a conductive pulley-in a, region near ground potential, an endless belt of insulating material passing over said pulleys, two inductor plates, respectively closely spaced to said belt at each of said pulleys, and means to establish an electric field between said inductor plates respectively and said pulleys so as to cause the flow of electric charge between said pulleys and the said belt, thereby eliminating the necessity of gaseous ionization.

12. High voltage apparatus consisting of a metallic terminal to which charges are transferred, insulating means for the physical support of said terminal, an endless traveling belt constituting a charge conveyor, means for electrostatically inducing charge to flow onto said belt, a metal charging pulley with which successive portions of said belt are momentarily in contact, and means for inducing the charges to flow from the said belt to said metallic terminal, the means for electrostatically inducing charge to flow onto said belt including an inductor plate closely spaced with respect to the outer surface of said belt, and the means for electrostatically inducing charge to flow from said belt to said terminal including an inductor plate closely spaced with respect to the outer surface of said belt and in proximity to said terminal, thereby eliminating the necessity of gaseous ionization.

13. High voltage apparatus consisting of a metallic terminal to which charges are transferred, insulating means for the physical support of said terminal, an endless traveling belt constituting a charge conveyor, means for electrostatically inducing charge to flow onto said belt, a metal charging pulley with which successive portions of said belt are momentarily in contact, and means for inducing the charges to flow from the said belt to said metallic terminal, the means for electrostatically inducing charge to flow onto said belt including an inductor plate closely spaced with respect to the outer surface of said belt, and the means for electrostatically inducing charge to flow from said belt to said terminal including an inductor plate closely spaced with respect to the outer surface of said belt and in proximity to said terminal, said endless traveling belt being essentially insulating but with a relatively thin semi-conducting sheath at its inner surface, thereby eliminating the necessity of gaseous ionizatron.

14. High voltage apparatus for electrostatically inducing a flow of charge to a charge conveyorwithin a chamber containing gas under high pressure, and without re sulting gaseous ionization, comprising the following: a chamber provided for the purposeof and adapted to contain a gaseous medium under high pressure; a charge conveyor of a semi-conducting character within said chamber; means to impart rapid traveling movement to said charge conveyor within said chamber when so filled with gas under high pressure; an inductor member within the chamber and closely spaced to the conveyor; and a source of charge supply for maintaining a potential of one sign upon said inductor member; said semi-conductive conveyor and said maintained-potential inductor member constituting means for electrically inducing electric charge of opposite sign to flow from said inductor member to said charge conveyor while the latter is so traveling Within said chamber, and without creating gaseous ionization within said chamber with resulting dissociation of gas molecules that would increase their chemical activity.

15. High potential electrostatic apparatus wherein, for transferring electric charge to and from a metallic terminal, there is provided an endless belt that passes over pulleys having conducting surfaces, and which belt is essentially of an insulating character of material, but which belt is provided upon its inner surface that contacts with said pulleys with a relatively thin semi-conducting sheath of relatively lower resistivity material for a given leakage of electric charge along the belt under the impetus of the voltage of the generator, the resistivity of such semi-conducting sheath lying in the range from 10 ohm cm. to 10 ohm cm.

16. High potential electrostatic apparatus in accordance with claim 15, wherein the semi-conducting sheath is a rubber compound.

17. In the generation of high potential electrostatic charges in a gas-pressurized chamber, the step which comprises rapidly moving a semi-conducting charge conveyor surface in the chamber in passing contact with a metallic or other conductive surface and in closely spaced proximity to an inductor thereby to transfer electric charge from one to the other surface with avoidance of attendant gaseous ionization.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 479,941 Henry Aug. 2, 1892 2,070,972 Lindenblad Feb. 16, 1937 2,486,140 Felici Oct. 25, 1949 2,568,824 Rahbek Sept. 25, 1951

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