US3581106A

US3581106A - Graded plane, high voltage dc power supply

Info

Publication number: US3581106A
Application number: US719107A
Authority: US
Inventors: Joseph T Peoples; Charles C Landry
Original assignee: Nuclear Chicago Corp
Current assignee: Nuclear Chicago Corp
Priority date: 1968-04-05
Filing date: 1968-04-05
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25
Also published as: GB1255342A; NL6905240A; DE1917253A1; JPS4818730B1; FR2005653A1

Abstract

A high voltage electron accelerator system employing a graded plane power supply, a graded plane accelerator, and a single, graded-conductor cable interconnecting the power supply and the accelerator.

Description

United States Patent [50] Field0fSearch........................................... 307/110, 147, 149, 150; 313/63; 321/15; 328/233, 256

[72] inventors Joseph T. Peoples;

Charles C. Landry, Austin, Tex.

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AFPA

Primary Examiner-Raymond F. Hossfeld Attorneys-Lowell C. Bergstedt, Walter C. Ramm and 54 GRADED PLANE, HIGH VOLTAGE DC POWER Helmuth wegne SUPPLY 7 Clams 6 Drawmg ABSTRACT: A high voltage electron accelerator system employing a graded plane power supply, a graded plane accelera- 321/15, 328/233, 328/256 tor, and a single, graded-conductor cable interconnecting the [51] Int. H02j 5/00 power supply andthe accelerator.

PATENTEU HAY25 l9?! SHEET 2 [IF 4 MI Pea-Ira ozse k (a a? M61163 ,4 arraewr GRADED PLANE, IIIGII VOLTAGE DC POWER SUPPLY Developing industrial applications for high energy electron beams have produced an expanding demand for high voltage accelerator systems which are not only capable of producing high energy electron beams, but are capable of continuous operation for long periods of time. These accelerator systems must also be relatively inexpensive from initial capital investment and operating and maintenance cost standpoints. The production of high energy beams of charged particles other than electrons, such as protons, deuterons, and even heavier charged particles, is also of considerable interest to the scientific community.

One type of high voltage accelerator system which has been developed is comprised essentially of a high voltage DC power supply, an accelerator utilizing the DC voltage produced by the power supply to accelerate an ion beam, and a cable system for carrying the high voltage power to the accelerator. Typically, the accelerator also requires additional, low voltage power for production of the charged particles to be accelerated, so this must be produced in the power supply and transmitted to the accelerator via the cable system.

The magnitudes of DC voltage which are of interest for some industrial and other type applications of accelerator systems lie in the l --l,000 kv. (kilovolt) range. The problems involved in the production of DC voltages of these magnitudes by conversion of an available signal from an AC power source are well known to those familiar with this art. Transformers for conversion from low voltage AC to high voltage AC are quite readily available, and circuitry of various types for AC to DC voltage conversion are well known; but the concurrent problems of providing adequate heat dissipation, controlling and stabilizing the high DC voltage produced, and keeping the dimensions of the power supply enclosure down to manageable proportions are not easily reconciled.

Therefore, the principal object of this invention is to provide an improved high voltage DC power supply.

Another object of this invention is to provide an improved high voltage DC power supply for a high voltage accelerator system.

In accordance with this invention a power supply enclosure means for containing a quantity of electrically insulating fluid is provided with a plurality of voltage grading means for stabilizing the high voltage produced within the enclosure, each of the voltage grading means including a plurality of equipotential planes mounted in spaced-apart relation to each other with a stepwise gradient of voltages from the high voltage to a ground reference voltage thereon.

In a preferred embodiment of the invention involving a voltage doubler type of power supply, three series of equipotential planes, associated circuitwise with rectifiers, capacitors, and resistors, are mounted in two separated stacks between opposing walls of the power supply enclosure which are at ground potential, with the series of planes associated with the capacitors apportioned between the two stacks. One of the two portions of capacitor planes is electrically insulated from the nearest walland the other portion utilizes that wall as a ground reference plane. The ground reference planes of the rectifier and resistor series of planes are provided with ground reference voltage by the opposite wall of the enclosure. The electrical components such as resistors, capacitors, and rectifiers are mounted between individual ones of their respective planes.

The primary advantages of the graded plane power supply of this invention are the reduction in power supply enclosure dimensions and the increase in power supply stability or freedom from discharges between physical points within the enclosure which are at different electrical potentials. This is particularly effectively accomplished in the preferred embodiment of the graded plane power supply because only two separated stacks of planes are required, and the planes which have the highest DC voltage thereon do not look at ground planes with their flat sides but are provided with intervening planes having lower potentials thereon. Some of these same advantages would also attach to use of the graded plane concept wherein the three series of planes are mounted in three separate stacks, but a rather large separation distance between planes carrying the highest DC voltage and the ground reference planes seen by their flat sides would have to be provided. Thus, it can be said that some grading of the power supply potentials always works a size reduction, but overall grading of the potentials provides the greatest size reduction advantage and, at the same time, the important advantage of increased operating stability.

Other objects, features, and advantages of this invention will be apparent from a consideration of the detailed description below together with the accompanying drawings in which:

FIG. 1 is essentially a schematic diagram of a graded high voltage electron accelerator system including a graded cable DC transmission system;

FIG. 2 is an elevational view of the basic mechanical arrangement of the power supply shown schematically in FIG. 1;

FIG. 3 is a top view of the power supply of FIG. 2;

FIG. 4 is an elevational view of an accelerator head according to a prior art construction;

FIG. 5 is an elevational view of the basic mechanical arrangement of the accelerator shown schematically in FIG. 1; and

FIG. 6 is a partly sectioned, elevational view of a graded high voltage cable of a particular type of construction.

Referring now to FIG. 1, the three basic components of a.

graded high voltage accelerator system are shown as a graded high voltage DC power supply 100, a graded high voltage accelerator 200, and a graded high voltage DC power transmis:

sion cable 300. Power supply 100 is one of a voltage doubler type in which an AC line voltage is first transformed to provide a high voltage AC signal, and then the high voltage AC signal is rectified to produce a corresponding DC voltage. The particulars of the operation of a voltage doubler type of DC power supply need not be given here because they are well known to those skilled in the art.

As shown in FIG. I, a series of equipotential planes 1-11 are interconnected by a series of rectifiers 30, a series of resistors 31, and a series of capacitors 32. The primary electrical function provided by this group of elements is the rectification accomplished by the rectifiers 30, with the capacitors 32 serving as transient equalizers and with the resistors 31 aiding in the equipotential voltage grading of the rectifier planes. Equipotential plane 1 1 also serves as one of the planes in a series composed of planes 11-20 which are interconnected by three series of capacitors 40 and a series of resistors 41. It should be understood that the rectifier symbol 30 may designate a plurality of rectifiers in series between respective equipotential planes if such plurality is needed in terms of the actual voltage parameters and similarly for resistors 31 and capacitors 32. Moreover, the number and types of such elements may vary from one application to another, as desired.

Planes

15 and 16 in the capacitor series of planes are directly connected by a lead 88 since these planes are functioning at the same potential. The reason for this will become apparent from a consideration of the physical arrangement later discussed. Plane 20 is actually the bottom of a tank which is at ground reference potential, and plane 1 is associated with top 28 of the tank which is at ground reference potential also.

Plane 11, the common plane of the rectifier and capacitor series of planes is connected via a resistive element 50 to plane 21 in a series of planes 21-27 which are interconnected by

resistors

60 and 61. The

resistor symbols

60 and 61 may actually correspond to a plurality of individual resistors connected in series between each plane. Plane 27 is associated with top 28 of the tank and is accordingly at ground reference potential. Plane 6 in the rectifier series and plane 15 in the capacitor series are connected via cables 72 and 71, respectively, to secondary winding terminals 73 and 74 on a high voltage transfonner 70. Power for transformer 70 is supplied via cables 81 and 82 from a power supply external to the tank. A high voltage AC signal across terminals 73, 74 is rectified to produce a corresponding high voltage DC signal on equipotential'plane 11 and also on equipotential plane 21. Voltage grading of equipotential planes 1-11 is a varying voltage grading, while that on planes 11-20 and planes 21- -27 is substantially constant voltage grading with only slight amounts of ripple thereon. Transformer 75 is an isolation transformer powered by power supply 85 over

cables

86 and 87, and it produces an AC signal across its secondary winding terminals 78 and 79.

The electrical aspects of a high voltage electron accelerator 200 are also shown in FIG. 1. Planes 110-116 are graded equipotential planes with planes 11-114 serving as accelerating electrodes, plane 115 together with cup 122 sewing as a beam extracting system of electrodes, and plane 116 serving as a high voltage plane associated with filament 120. Shield 117 is also associated with plane 116 and filament 120, being connected thereto via lead 118. Electrons emitted by filament 120 are accelerated by electrodes 110-115 and become a high velocity electron beam 123 which is capable of performing various typesof desired work. In some applications the electron beam is scanned in a rectilinear fashion after acceleration to provide electron irradiation of a width of material. Power for the various elements of accelerator 200 is transmitted thereto from power supply 100 by way of a graded cable 300. Graded cable 300 consists of a plurality of concentric conductors 210-270 surrounding a central wire 280. The seven concentric conductors 210-270 are connected at one end to planes 21-27 in power supply 100 via leads 61-67 and at the other end to planes 1 -116 in accelerator 200 via leads 130-135 and lead 118 together with shield 117. In this fashion the graded voltages on equipotential planes 21-27 in power supply 100 are directly connected to associated planes 110-116 in accelerator 200 via a single cable. Central wire 280 carries AC power from isolation transformer 75 to filament 120 to heat filament 120 and produce emission of electrons for acceleration.

FIGS. 2 and 3 show, respectively, a side and a top view of the mechanical arrangement of power supply 100 and one end of graded cable 300 associated therewith. It should be understood that the various electrical elements such as resistors, capacitors, and'rectifiers, shown schematically in FIG. 1 are physically located between the individual discs serving as equipotential planes. As shown, high voltage transformer 70 occupies one whole side of the power supply enclosure, and isolation transformer 75 occupies a comer of the enclosure on the other side thereof.

Discs 1-27 which serve as equipotential planes are mounted in two separate stacks between top 28 and bottom of the enclosure. Disc 3 is shown in cross section to illustrate the typical cross-sectional profile of discs 1-27. As can be seen, the discs which serve as equipotential planes carrying the highest DC voltage (300 kv.) are separated from the top 28 and bottom 20 of the enclosure, and therefore do not look with their flat sides at a ground plane. The dual stack arrangement serves to conserve space in the power supply, and thus the power supply enclosure can be smaller. This is a distinct advantage from a cost savings standpoint since the enclosure will cost less and the factory or laboratory space needed to house the power supply can be reduced. Moreover, the separation of the highest voltage planes from the top and bottom of the enclosure with intervening graded voltage planes reduces the likelihood of sparking in the power supply, and this ishighly advantageous because such discharges cause an expensive failure of the system involving likely damage to rectifiers and other elements which must then be replaced during consequent down time.

One of the primary advantages of the graded plane power supply is the size reduction achieved by grading the voltage gap between 300 kv. and ground with a plurality of equipotential planes. As is well known, the power supply enclosure will be filled with an insulating fluid, typically a nonconductive oil. The separation distance required between a 300 kv. point and a ground point with only insulating oil intervening would be very great, but considerably less overall separation is required when graded planes intervene. This follows from the nonlinear relationship between insulator thickness and breakdown voltage so that less intervening distance with insulating fluid filling it is required when graded planes are used between 300 kv. planes and ground planes. A further advantage is the added stability of the power supply achieved as a result of the graded equipotential planes serving to provide a uniform voltage gradient throughout the power supply enclosure.

As shown in FIG. 2, capacitor equipotential planes 16-19 are mounted on three insulating columns or poles 43; and the remainder of the capacitor equipotential planes 11-15 are mounted on another three insulating columns 42. Resistor equipotential planes 21-27. are shown mounted on a single insulating column 29 which is supported on plane 16. Plane 27 is associated with the top 28 of the power supply enclosure. Rectifier equipotential planes 1-10 are shown mounted on a single insulating column 33 which is supported on plane 11. Plane 1 is associated with the top 28 of the power supply enclosure. Typically, planes 1-10 with column 33 and planes 21-27 with column 29 will be mechanically constructed so that they can be removed from the enclosure as a unit for ease in servicing the power supply. Moreover, an additional plane or disc could be added at the bottom of rectifier series 1-10 with a jack-in relation to plane 11 to enable reversal of power supply polarity by flipping over that unit.

Resistors

51, 52, and 53 are shown connecting plane 11 to plane 21. These resistors are limiting resistors which protect the rectifiers associated with planes 1-10 from surge current in the event of a short circuit in the accelerator or the cabling.

As shown in FIGS. 2 and 3, graded cable 300 extends through planes 21-27, and the respective concentric conductors 210-270 are bared at appropriate levels for connection to the respective planes. Center wire 280 extends through plane 21 and connects via lead 76 to isolation transformer 75. It should be readily understood that other mechanical associations between graded cable 300 and planes 21-27 and transformer 75 could also be implemented.

A 300 kv. power supply of the arrangement shown in FIGS. 2 and 3 can be constructed to have overall dimensions of approximately 5 6X5 feet, which is about half the size of many power supplies of other construction having the same rating. An actually constructed embodiment has been operated at 300 kv. with about 30- kilowatt-output power. From an industrial equipment standpoint a power supply of this rating and this overall size constitutes a real achievement. Furthermore, extension of the basic concepts or features of its construction to achieve power supplies with a 1,000 kv., kw. or higher rating is considered to be attainable with only relatively slight increases in overall size, possibly with greater numbers of graded planes in each stack.

In FIG. 4, a 300 kv. electron accelerator 400 of a particular prior art type is shown. A pair of

bulky cables

501 and 502 bring the high voltage DC power supply and an AC signal impressed on the high DC voltage. In this case the AC signal is transformed down'to a lower voltage by transformer 350 before applying it to the filament, although this is not always necessary since a lower voltage, higher current signal could be produced in the power supply and carried by the cables directly to the filament.

A large number of accelerating electrodes, for example the 20 electrodes 310-330 shown in FIG. 4, are required in the accelerating column for stable operation of this type of accelerator; and a resistor network 335 is required to provide a voltage dividing network for the respective electrodes. Individual rings of insulating material 331 support the electrodes, and the rings and electrodes are sealed so as to form a vacuum tight enclosure. The individual resistors in network 335 are required to be small and yet to be capable of operating at high power, and these two requirements are not readily reconciled. A rather high magnitude of current through the resistors of this network is desirable so that a stray electron beam will not disrupt the value of their IR drop, but a practical limit is placed on the possible current value because of the heat that is generated. Auxiliary cooling could be provided, but this is undesirable. Therefore, a 0.5 ma. current is a typical limit on the current through this resistor network. Expanding this design concept to provide an accelerator with a still higher voltage, higher power rating is not considered feasible except by greatly increasing the length of the accelerating column.

Larger power transmission cables would also be required for higher voltage operation. Consequently, it is believed that inherent limitations are present in this type of prior art accelerator design and that these limitations make this design a relatively unattractive approach to the construction of high voltage accelerators.

Contrasted to the prior art design shown in FIG. 4, an accelerator 200 of a graded plane design is shown in FIG. 5 in approximate relative size relationship. The comparative simplicity of design and reduction in size are apparent from this side-by-side comparison. Graded accelerator 200 has seven graded planes 110-116 connected to seven graded conductors 2l0270 in graded cable 300 via leads 130-135 and 118. These seven graded planes are mounted on a triangular array of three insulating columns 138 (only one shown) and cable 300 passes directly through the respective planes as in power supply 200 in FIG. 2. Each of the graded planes 111- 115 may have the same cross-sectional profile as that of plane or disc 3 in the power supply shown in FIG. 2.

Various types of construction can be employed for accelerating column 136, which is basically composed of internal electrodes (not shown) and cylindrical insulating members 137 mounted in a sandwichlike arrangement which must form a vacuumtight seal. The electrodes may be integral parts of their respective planes or discs, or they may be separate elements mounted to their respective planes. Conceivable, planes 111-416 may be made much smaller in diameter than shown in FIG. 5 so that the lip of the planes extending out from column 136 is only wide enough to accommodate the passage therethrough of the respective segments of cable 300. In such a construction, insulating columns like column 138 may not be required for supporting planes 111-416, rather the insulator rings 137 could themselves support the planes.

Typically a cylindrical, gastight shield will be mounted to base plane 110 and be filled with a nonconducting fluid, typically an insulating gas. This insulating gas provides the electrical insulation between respective planes, and prevents discharges or sparking therebetween. Conceivably planes 110- 116 could be surrounded by a vacuumtight enclosure with a high internal vacuum. This would further reduce the chances of sparking between planes, and it might make it possible to eliminate central accelerating column 136 altogether.

A readily apparent size advantage is achieved by constructing an accelerator according to the graded plane design as illustrated in FIG. 5. Principally, the size difference results from the shorter insulating column with fewer electrodes. This is made possible by locating the voltage divider resistors in the power supply where they can be cooled efficiently and thus can support a heavier current (on the order of 2.0 ma.) to stabilize the IR drop between respective planes in the accelerator. Also, the graded planes themselves provide for more uniform distributions of voltage gradients in the accelerator column area, and this provides for more stable operation of the accelerator with less likelihood of discharges between planes or between accelerating electrodes. Thus, the distance between

planes

110 and 116 in accelerator 200 in FIG. 5 may be as little as 10 inches compared to a distance of around 18 inches between planes 330 and 340 in accelerator 400 in FIG. 4. Moreover, as for power supply 100, it is believed that extension of this design concept to accelerators of greater than 300 kv. potential is readily achievable.

Additional important advantages attend the requirement of only one cable 300 to connect accelerator 200 to an appropriate power supply. These advantages include the ease of installation where the interconnecting cable is to be carried in conduit and the size advantage of the graded cable itself which is smaller in diameter than either of the

cables

501 and 502 in FIG. 4.

In FIG. 6 a particular construction of a graded cable is shown. A hollow copper tube 270 carries internally a wire 280 having a thin layer of insulation 416 thereon. A layer of insulation 415 surrounds copper tube 270, followed by a layer of conducting material 260 which is shown as a thin layer of metallic foil but may also be a layer of braided copper or any other conducting material. Braided copper has proved to be advantageously employed since it has greater resilience than a metal foil and is thus less likely to break under bending stress applied to the cable. Similar layers of insulating material 403 to 414 interspersed with layers of conducting material 220 to 250 round out the 8 conductor cable. 210 designates a rather thick layer of braided copper which forms the ground return braid of the cable which is, in turn, covered by a final layer of insulating material 401.

A process which has been employed for making relatively short (50 feet) lengths of this type of cable involves starting with copper tube 270 and disposing a length of a thin-wall, heat-shrinkable plastic tubing over it. Then the tubing is heated so that it shrinks over the copper tube and is bound thereto, forming insulating layer 415. A single layer of aluminum foil (e.g., approximately 4 mills thick) or, alternatively, a layer of braided copper (e.g., approximately 10 mills thick) is disposed over layer 415 to form conductor 260. Then another length of heat-shrinkable plastic tubing is disposed over conductor 260 and heated to bind both to the previously built-up structure. Second and third lengths of tubing may be employed to increase the thickness of the insulating layer as required. Repeating the above procedure enables one to build up any desired number of concentric conductors.

Using this procedure, starting with a 0.298 inch OD copper tube and using thin aluminum foil for conducting layers, a cable as shown in FIG. 6 has been constructed. The resulting overall diameter of the cable was about 1.2 inches, and the cable was successfully tested with 300 kv. on copper tube 270 and with approximately 60 kv. voltage drops between

respective conductors

270, 260, 250, 240, 230, 220, and 210. A cable has also been constructed with braided copper as the conducting layers, and it has only slightly larger diameter because of the thicker layers of conducting material. It is believed that greater than 300 kv. voltages can be carried by these cables, and there appears to be no reason to suspect that similarly constructed cables cannot be fabricated to carry upwards of 1,000 kv. perhaps with ten kv. gradings between innermost and outermost conductors. It should be clearly understood that other embodiments of graded cable and other methods for making it are within the scope and purview of this invention.

It should be understood that this invention is not limited to use in connection with accelerators or even graded cable transmission systems and, furthermore, is not limited to voltage doubler-type power supplies or to power supplies producing negative voltages. Thus, it is apparent that numerous modifications could be made by those skilled in the art without departing from the scope of this invention as claimed in the following claims.

I claim:

1. In a high voltage direct current power supply wherein the high DC voltage is produced by employing a plurality of electrically operative elements such as rectifiers, capacitors, and the like, the improved arrangement comprising:

power supply enclosure means for containing a quantity of electrically insulating fluid;

a plurality of voltage grading means mounted within said enclosure means for stabilizing the high voltage produced, each of said voltage grading means including a plurality of equipotential planes mounted in spaced-apart relation to each other with a stepwise gradient of voltages from said high voltage on a central plane to a ground reference voltage on an end plane, said electrically operative elements being mounted between individual ones of said equipotential planes and being connected therebetween to produce said stepwise gradient of voltages.

2. The arrangement as claimed in claim ll, wherein said enclosure meansincludes a pair of opposing walls having substantially groundreference potential thereon; the number of said voltage grading means is three; the first, second, and third ones of said voltage grading means having primarily associated therewith rectifiers, capacitors, and resistors, respectively; said first, second and third voltage grading means being arranged in two separated stacks between said opposing walls such that the equipotential planes which carry the highest DC voltage are spaced from said opposing walls with at least one equipotential plane which carries a lower voltage is interposed between each of said last-mentioned planes and said opposing walls, thereby reducing the tendency for sparking to occur in said power supply.

3. In a high voltage, direct current power supply of the voltage doubler-type having the components thereof immersed in a bath of electrically insulating oil, the improved arrangement comprising:

a plurality of equipotential planes operatively grouped as rectifier planes, capacitor planes, and resistor planes; said planes being arranged in two separated stacks of spacedapart planes with all of said rectifier planes and a first portion of said capacitor planes in a first one of said stacks and with all of said resistor planes and the remaining portion of said capacitor planes in a second one of said stacks; said planes in each of said stacks being graded voltagewise with lower voltages on planes at each end and higher voltage on central planes.

4. The arrangement as claimed in claim 3, wherein said two stacks of planes are mounted between a pair of opposing walls providing ground reference potential thereon; one of said walls providing ground potential for said rectifier planes and said resistor planes; the other of said walls providing ground reference potential for said capacitor planes and being electrically insulated from said first portion of said capacitor planes.

5. In a high voltage, direct current power supply:

a tank having electrically conducting walls and being capable of containing a column of electrically insulating fluid;

a high voltage transformer mounted on the bottom of said tank;

a plurality of electrically conducting discs mounted in spaced-apart relation in two separate stacks between two opposing walls of said tank;

a plurality of rectifiers coupled in series between a first preselected, centrally located disc in one of said stacks and one of said opposing walls with successive intervening discs serving as graded equipotential rectifier planes;

' a plurality of capacitors coupled in series between said first preselected disc and the disc adjacent the other of said walls with successive intervening discs serving as graded equipotential capacitor planes;

a plurality of resistors coupled in series between a second preselected, centrally located disc in the other of said stacks and one of said opposing walls with successive intervening discs serving as graded equipotential resistor planes;

a plurality of capacitors coupled in series between the other of said opposing walls and the disc adjacent said second preselected disc with successive intervening discs serving as graded equipotential capacitor planes;

means for direct current connecting the series of capacitor coupled discs in one stack with the series of capacitor coupled discs in the other stack;

at least one series resistor connected between said first and second preselected discs; and

circuit connections between said high voltage transformer and a preselected one of said rectifier planes and a preselected one of said capacitor planes; whereby said power supply is capable of producing a highly stable high DC voltage on said first and second preselected discs.

6. Apparatus as claimed in claim 5, wherein said plurality of rectifiers and said rectifier planes are so constructed and arranged that the may be removed from said tank as a single structural unit or ease of maintenance and for ease in changing the polarity of the high DC voltage produced by said power supply; and said tank includes an access port associated with said structural unit.

7. Apparatus as claimed in claim 6, wherein said plurality of resistors and said resistor planes are so constructed and arranged that they may be removed from said tank as a single structural unit for ease of maintenance thereof; and said tank includes a second access port associated with said structural unit.

Claims

1. In a high voltage direct current power supply wherein the high DC voltage is produced by employing a plurality of electrically operative elements such as rectifiers, capacitors, and the like, the improved arrangement comprising: power supply enclosure means for containing a quantity of electrically insulating fluid; a plurality of voltage grading means mounted within said enclosure means for stabilizing the high voltage produced, each of said voltage grading means including a plurality of equipotential planes mounted in spaced-apart relation to each other with a stepwise gradient of voltages from said high voltage on a central plane to a ground reference voltage on an end plane, said electrically operative elements being mounted between individual ones of said equipotential planes and being connected therebetween to produce said stepwise gradient of voltages.

2. The arrangement as claimed in claim 1, wherein said enclosure means includes a pair of opposing walls having substantially ground reference potential thereon; the number of said voltage grading means is three; the first, second, and third ones of said voltage grading means having primarily associated therewith rectifiers, capacitors, and resistors, respectively; said first, second and third voltage grading means being arranged in two separated stacks between said opposing walls such that the equipotential planes which carry the highest DC voltage are spaced from said opposing walls with at least one equipotential plane which carries a lower voltage is interposed between each of said last-mentioned planes and said opposing walls, thereby reducing the tendency for sparking to occur in said power supply.

3. In a high voltage, direct current power supply of the voltage doubler-type having the components thereof immersed in a bath of electrically insulating oil, the improved arrangement comprising: a plurality of equipotential planes operatively grouped as rectifier planes, capacitor planes, and resistor planes; said planes being arranged in two separated stacks of spaced-apart planes with all of said rectifier planes and a first portion of said capacitor planes in a first one of saiD stacks and with all of said resistor planes and the remaining portion of said capacitor planes in a second one of said stacks; said planes in each of said stacks being graded voltagewise with lower voltages on planes at each end and higher voltage on central planes.

5. In a high voltage, direct current power supply: a tank having electrically conducting walls and being capable of containing a column of electrically insulating fluid; a high voltage transformer mounted on the bottom of said tank; a plurality of electrically conducting discs mounted in spaced-apart relation in two separate stacks between two opposing walls of said tank; a plurality of rectifiers coupled in series between a first preselected, centrally located disc in one of said stacks and one of said opposing walls with successive intervening discs serving as graded equipotential rectifier planes; a plurality of capacitors coupled in series between said first preselected disc and the disc adjacent the other of said walls with successive intervening discs serving as graded equipotential capacitor planes; a plurality of resistors coupled in series between a second preselected, centrally located disc in the other of said stacks and one of said opposing walls with successive intervening discs serving as graded equipotential resistor planes; a plurality of capacitors coupled in series between the other of said opposing walls and the disc adjacent said second preselected disc with successive intervening discs serving as graded equipotential capacitor planes; means for direct current connecting the series of capacitor coupled discs in one stack with the series of capacitor coupled discs in the other stack; at least one series resistor connected between said first and second preselected discs; and circuit connections between said high voltage transformer and a preselected one of said rectifier planes and a preselected one of said capacitor planes; whereby said power supply is capable of producing a highly stable high DC voltage on said first and second preselected discs.

6. Apparatus as claimed in claim 5, wherein said plurality of rectifiers and said rectifier planes are so constructed and arranged that they may be removed from said tank as a single structural unit for ease of maintenance and for ease in changing the polarity of the high DC voltage produced by said power supply; and said tank includes an access port associated with said structural unit.