US3678365A

US3678365A - Waveguide device for bringing an element to a high direct-current potential

Info

Publication number: US3678365A
Application number: US91766A
Authority: US
Inventors: Charles Fremiot
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1969-11-27
Filing date: 1970-11-23
Publication date: 1972-07-18
Anticipated expiration: 1989-07-18
Also published as: GB1300983A; JPS4825138B1; DE2058470A1; FR2068094A5

Abstract

A DC high voltage source comprising a plurality of modules whose outputs are connected in series ending relation and each having a microwave receiving antenna and a rectifier, each receiving antenna is couplet with a respective transmitting antennae fed by a magnetron through a waveguide. The microwaves are preferably modulated at radiofrequency and each module then comprises a step up transformer.

Description

United States Patent Fremiot [451 July 18, 1972 [54] WAVEGUIDE DEVICE FOR BRINGING [56] References Cited I g F 5, 2 ?J DIRECT- UNITED STATES PATENTS 2,695,374 11/1954 Je son ..321/15 X [721 lnvemo" Charles Gremble, France 3,434,678 3/1969 Br vn et al ..32l/8 x 73 A I C miss t A At 3,543,136 11/1970 Enge.... ....32i/l5 Sslgnee 2; :5: ergie omique 3,568,035 3/1971 Pierson.... ....321/15 3,535,543 10/1970 Dailey ..32l/8 X [22] Filed: Nov. 23, 1970 Primary ExaminerWilliam H. Beha, Jr. [2]] Appl' 9l766 Attorney-Lane, Aitken, Dunner & Ziems [30] Foreign Application Priority Data [57] ABSTRACT Nov. 27 1969 France ..6940998 A DC high "wage a pluraliy "Mules whose outputs are connected in series ending relation and [52] U S Cl 321/81 321/15 321/27 R each having a microwave receiving antenna and a rectifier,

307 I151 each receiving antenna is couple! with a respective trans- 5 l t Cl H02 7 02 mitting antennae fed by a magnetron through a waveguide. E The microwaves are preferably modulated at radiofrequency Oscillator and each module then comprises a step up transformer.

13 Claims, 4 Drawing Figures Modu/akar PATENTEDJUL18|912 3,678,365

SHEET 1 UP 3 Q FIG 2 1 s g g 4; L 44 l .Detecllzlr Rect/F/Pr networ network I INVENTOR EYS PATENTED JULI8|972 3,678,365

SHEET 2 OF 3 INVENTOR Claw/was flips/var ATTUR LYS PAn-immuuamz 3.678 865 SHEET ,3 0F 3 INVENTOR 62/124 as kew or WAVEGUIDE DEVICE FOR BRINGING AN ELEMENT TO A HIGH DIRECT-CURRENT POTENTIAL The present invention relates to a device for creating a high direct-current electric potential between a part and ground, said device being suitable for use as a source of the DC highvoltage necessary for operation of a charged-particle accelerator.

Prior art devices adapted to provide a high direct-current potential difference between ground and an insulated element consist of an array of series-connected modules each comprisng a 9lt s ep-2P. WWEU EF a rsqtt i r swir filter: modules of this type are perfectly adapted to deliver directcurrent voltages up to 50 kV each. One would expect that any direct-current voltage which is required could be obtained simply by associating a sufficient number of modules in series. In fact, the number of modules is limited in practice by technological difficulties the alternating-current source which supplies all the modules is nearly at ground potential whereas the succesive modules are brought to potentials which increase from each module to the next. Thus, it becomes more and more difficult to ensure insulation of the last modules as the DC voltage increases with respect to ground.

The present invention is intended to provide a device for bringing an element to a high direct-current potential with respect to ground which improves upon the prior art devices.

To this end, the invention proposes a device comprising a plurality of cells each provided with a rectifier and connected in series, said device being essentially distinguished by the fact that each cell is supplied with electric current by a microwave receiving antenna coupled with a transmitting antenna which is supplied by a waveguide from a microwave generator, the transmitting antennae being connected to ground as well as the generator and the waveguide. One advantage of this arrangement can immediately be appreciated the microwave radiation can be focused by means of directional antennae with relative ease, thus permitting of satisfactory powertransfer efficiency.

The transmitting antennae can either be all supplied by the same waveguide or supplied by different generators and waveguides, thereby circumventing the problems relating to maintenance in phase. The receiving antenna of each cell preferably supplies a detection device constituted by a semiconductor diode, for example. Since it is preferable to reduce the number of cells, the rectifier of each cell must be supplied with a potential difference which is as high as possible. In consequence, a voltage step-up transformer will advantageously be inserted between the rectifier and the detector device. In view of the fact that said transformer (and also the filter device which is placed at the output of the rectifier) will have dimensions which are smaller as the frequency of the transformer supply current is higher, it will be preferable either to modulate the microwave generator or (if this latter produces a direct-current high-frequency power) to chop the output voltage received from the detector device. The modulation frequency can range from a few tens to a few hundreds of kc/s.

It will usually be an advantage to employ a microwave generator of the magnetron type since this latter is more economical than a klystron system and no use is made of the frequency-changing possibilities which are offered by this latter.

A more complete understanding of the invention will be gained from the following description of a device which constitutes one exemplified embodiment of the invention and is given without any implied limitation, reference being made to the accompanying drawings, in which FIG. 1 is a highly schematic block diagram of the device FIG. 2 is a schematic diagram showing one of the cells of the device of FIG. 1 I

FIG. 3 is a sectional view showing the main components of a device which constitutes an alternative form of the device represented in FIG. I, this view being taken along the midplane of the bell-housing FIG. 4 is a sectional view taken along line IVIV of FIG. 3.

The device which is illustrated in FIG. 1 comprises a metallic bell-housing 10 containing a gas having a high insulating capacity such as sulphur hexafluoride under a pressure of a few bars.

Cells

12,, 12 12,,(n being the number of cells) are disposed within said bell-housing 10, a direct-current voltage U being delivered across the output terminals of each cell. All the outputs are connected in series between the bell-housing which is connected to ground and a high-voltage output 16 which passes through the bell-housing within an insulating bushing 18. A leakage resistor of several megohms connects the output 18 to ground through a resistor 22 of lower value in order to constitute a voltage-dividing bridge, the function of which will become apparent hereinafter. The circuit is shown as having positive polarity but the principle applies without modification to the case of negative polarity.

All the cells are supplied through the same rectangular-section waveguide 24 which is supplied by a conventional microwave oscillator 26 of the magnetron type. By way of example, said oscillator can operate in the S-band at a wavelength of 10 cm. A resistive or reactive attenuator 28 is interposed in the waveguide 24. Couplers are placed at uniform intervals along the waveguide for the supply of transmitting

antennae

30,, 30 30,, which are each associated with one cell. The attenuator 28 is controlled by a circuit 32 which restores the voltage at the terminals of the resistor 22 to a constant value, said voltage being such as to represent a predetermined fraction of the total direct-current voltage supplied by the device.

The device which is illustrated in FIG. 1 is of a type in which the high-frequency power produced by the magnetron generator 26 is modulated by a modulator 34 having a frequency of kc/s, for example.

The

receiving antennae

36,, 36 36,, which are each associated with one cell are placed opposite to the transmitting

antennae

30,, 30 30,,. The antennae and in particular the transmitting antennae are advantageously dielectric in order that no communication should be established between the interior of the bell-housing 10 and the waveguide 24 while focusing the radiation it is thus possible to replace the magnetron without thereby making it necessary to restore the interior of the bell-housing to the pressure and composition of atmospheric air.

The distance to be maintained between the transmitting antenna 30,, and the corresponding receiving antenna 36,, will evidently depend on the voltage developed between these latter. In the case of a voltage of the order of l megavolt, a distance of 5 cm would theoretically be sufficient in the case of this potential difference within sulphur hexafluoride under a pressure of 7.5 bars. In practice, a distance of the order of 10 cm can be adopted.

All the cells have the same construction. The cell 12, which is illustrated in FIG. 2 comprises a detector circuit 38 which is supplied by the antenna 36, and which delivers an electric current at the modulation frequency of 100 kc/s, for example, to the primary winding of a transformer 40. Said transformer 40 operates as a voltage multiplier so as to deliver to a rectifier circuit 42 an rrns voltage of several tens of kV (50 kV, for example). A smoothing capacitor 44 can be placed between the output terminals of the rectifier.

The device which has just been described can also comprise a system for power transmission to an element which is brought to one of the output potentials 12,, l2, (such as a heating filament, for example). A magnetron oscillator then supplies a waveguide (not shown) which is separate from the previous waveguide and terminates in a single transmitting antenna which is coupled with a receiving antenna whose output supplies the element which is brought to a high voltage. This supply is often carried out at a high current intensity and a very low voltage and it is in that case not necessary to make provision for a step-up transformer and rectifier.

There will now be given by way of example the principal characteristics of a device which is intended to provide a potential difference of 1 megavolt and a leakage current of 0.1 mA and therefore a power of 100 W.

The oscillator is a magnetron which delivers a direct-current power of 1.5 kW, namely an actual power of the order of 1 kW. The device has twenty stages each providing a potential difference of 50 kV and a power of W-with a transformation efficiency of 50 percent.

It is known that the ratio between the values of power Pe and Pr transmitted by one antenna and received by the other is related to the effective areas of the antennae (it is assumed that both these areas are equal to S), to the wavelength L and to the distance D between the antennae by the relation Pr S 2 Fe LD This formula is strictly valid only if D is substantially higher than L which is not the case in this instance since D and L are of the same order. But the formula gives pessimistic results in this case and can therefore be employed as a first approximation.

It is possible to deduce from the formula the minimum effective area of each antenna In the case of the above values, Pe 50 W, Pr= W and L 10 cm and in respect of a distance of S cm between the antennae, it is found that S 22 cm approximately. This result is readily attained since it corresponds to a low antenna gain. In the case of a dielectric antenna, effective areas greater than I00 cm are achieved.

The device which is illustrated in FIGS. 3 and 4 constitutes an alternative form of the device shown in FIG. 1 and is intended to produce a direct'current voltage of I50 kV. The elements which are shown in FIGS. 3 and 4 and correspond to those of FIG. 1 bear the same reference numerals each followed by the prime index. It should be noted that the actual arrangement is much more compact than has been shown in FIGS. 3-4 the overall size is thus reduced subject to the penalty of a lesser degree of accessibility to the different components.

The device which is illustrated in FIGS. 3 and 4 comprises a metal bell-housing 10 (of stainless steel, for example) which is constituted by a metal base-plate 46, a shell 48 and a detachable cover 50. The shell is welded to the base-plate 46. An O-ring seal 52 formed of elastomer material is interposed between the cover 50 and the shell 48.

The three cells which are disposed within the bell-housing 10' are of identical construction. For example, the cell 12' is mounted between two

plates

44 and 46, the lower plate being fitted with a toric ring 58 for distribution of equipotential lines. Insulating columns 60 serve to maintain all the plates in spaced relation. The cell 12, which is supplied by a receiving antenna 36 comprises a detector circuit 38, a step-up voltage transformer 40 having a ferromagnetic core and low highfrequency losses, diodes 42' which constitute a rectifier circuit and smoothing capacitors 44. For the sake of enhanced clarity, the electric connections have not been shown in the figure. A resistor chain for regulating the voltage has a top portion which is molded within an insulating cylinder 62 of araldite and a bottom portion which is connected at 32 to a control device which is not illustrated.

The receiving antennae are coupled with three transmitting antennae which are supplied from the same waveguide 24'. The antenna 30',, for example, is coupled with the waveguide 24' through a slot closed by a window 63 which makes the bell-housing leak-tight and serves to fill this latter with suplur hexafluoride under pressure which is introduced through a pipe 64. Born antennae are employed in the embodiment which is illustrated in FIGS. 3 and 4 but other types could be employed (antennae of the dielectric or slot type, for example).

The electric circuit which is associated with the device of FIGS. 3 and 4 (but which is not illustrated in these latter) comprises a magnetron oscillator which operates at a frequency of 2,450 Mc/s and provides a direct-current power output of 1.5 kW. The modulator which is associated with the magnetron comprises a driver stage of conventional design which is capable of delivering pulses having a calibrated duration and a repetition frequency which is also calibrated l0 kc/s, for example). Said driver stage can consist of a flip-flop controlled by two unijunction transistors. The modulator also comprises a power stage which is supplied at an adjustable voltage and delivers to the magnetron the power which is necessary for its operation. Said power stage is constituted, for example, by a group of 18 transistors which are mounted in parallel and distributed in three groups controlled by the driver stage through impedance matching transistors which are mounted as an emitter-follower circuit. The power delivered by the magnetron is regulated by modification of the supply voltage. Provision is made for manual adjustment of the voltage supplied and for a device which carries out automatic stabilization after adjustment. The stabilizing device comprises a control circuit which compares the output signal delivered by the voltage-dividing resistance bridge with a reference voltage supplied by a voltage generator which is stabilized by a gas tube. In this case, the control is therefore carried out by producing action on the supply voltage of the modulator. The regulation could also be carried out as in the case of FIG. 1 by means of an attenuator which is interposed in the waveguide and comprises p-i-n diodes, for example.

The advantages of the device in accordance with the invention as compared with the solutions of the prior art have been clearly brought out in the foregoing description. Thus, the antennae can be spaced at any distance which may be necessary in order to solve problems of insulation, adjustments being carried out without any difficulty since the attenuator (and more generally the complete waveguide assembly) is connected to ground and the entire system is static. This last-mentioned feature represents a considerable improvement upon the Van de Graaff accelerator inasmuch as this latter entails the use of moving mechanical components which are subject to wear, the replacement of these components being complicated by the fact that they are enclosed within the pressurized enclosure. Moreover, the capital cost of a magnetron which would have represented a disadvantage a few years ago is now appreciably lower. Finally, any single-stage power transmission can be carried out by means of a system whose design principle is very similar to the device which serves to establish a direct-current potential difference.

Iclaim:

l. A device for providing a high DC potential between an element and ground, comprising:

microwave generator means;

waveguide means fed by said generator means;

a plurality of modules electrically insulated from each other, each said module having a microwave receiving antenna and a rectifier connected thereto;

means for electrically interconnecting the DC outputs of each said rectifier in a series-aiding relationship;

a plurality of transmitting antennae fed by said waveguide means respectively coupled with corresponding ones of said microwave receiving antennae and being positioned at a distance therefrom sufficient to provide electrical insulation; and

means for grounding said generator means, waveguide means, transmitting antennae and one of the DC outputs of a first one of said modules.

2. A device according to claim 13, wherein said microwave generator means includes a plurality of microwave generators and said waveguide means includes a plurality of waveguides fed respectively by said generators, each said transmitting antenna being supplied by a separate respective one of said waveguides 3. A device according to claim 1, wherein the microwave generator means is a magnetron oscillator.

4. A device according to claim 1, including additional means for supplying electric power to said element, said means comprising an additional receiving antenna carried by the elementand coupled to a transmitting antenna which is supplied by a waveguide from an additional microwave generator.

5. A device according to claim 1, further comprising a grounded bell-housing containing a dielectric gas in which said modules are operatively positioned, said transmitting antennae being mounted on said bell-housing and said microwave generator means being external to said bell-housmg.

6. A device for providing a large DC potential difference comprising a microwave generator a wave guide fed by said generator a plurality of directional transmitting antennae coupled to said wave guide and a plurality of modules each having a directional receiving antenna confronting a respective one of said transmitting antennae and spaced therefrom and rectifier means receiving energy from the receiving antenna, the outputs of the rectifiers of all modules being connected in series, said generator, waveguide and transmitting antennae being at the same DC potential. v

7. A device according to claim 6, wherein the generator is amplitude modulated at radio frequency and each module comprises detector means fed by the receiving antenna and a step-up transformer having its primary connected to said detector means and its secondary connected to said rectifier.

8. A device for providing a high DC potential between an element and ground, comprising:

microwave generator means;

waveguide means fed by said generator means;

a plurality of modules electrically insulated from each other, each module having a microwave receiving antenna and a rectifier connected thereto;

means for electrically interconnecting the DC outputs of each said rectifier in series-aiding relation;

a plurality of transmitting antennae fed by said waveguide means respectively coupled with corresponding ones of said microwave receiving antennae and being positioned at a distance therefrom sufi'rcient to provide electrical insulation;

means responsive to the highest DC output potential of said modules with respect to ground for attenuating the power fed to said transmitting antennae via said waveguide means; and

means for grounding said generator means, waveguide means, transmitting antennae and one of the DC outputs of 'a first one of said modules.

9. A device for providing a high DC potential between an element and ground, comprising:

microwave generator means;

means for modulating the microwave output of said generator means at a frequency lower than the frequency of the microwave output;

waveguide means fed by said generator means;

a plurality of modules electrically insulated from each other, each module having a microwave receiving antenna, a detection circuit for producing an output at the modulating frequency and a rectifier operatively receiving the output of said detection circuit;

means for electrically interconnecting the DC outputs of said rectifiers in a series-aiding relationship;

10. A device according to claim 9, wherein each said module includes a voltage step-up transformer operatively interposed between said detection circuit and said rectifier.

11. A device according to claim 10, wherein each said module includes a circuit which serves to chop the volt a e supplied by said detection circuit and dnves the primary wm ing of said voltage step-up transformer which supplies said rectifier.

12. A high voltage DC source, comprising electrically conductive grounded housing means for containing a pressurized dielectric gas having a plurality of gas-tight microwave ports formed therein, microwave source means located external to said housing for applying microwave energy through said ports, a plurality of directional microwave transmitting means mounted in said housing such that said microwave energy is fed from said microwave source means through said ports to said transmitting means respectively, a plurality of modules insulated from each other within said housing, each said module having directional microwave receiving means and a rectifying circuit coupled thereto, each said receiving means being operatively directed at a corresponding one of said transmitting means and spaced therefrom for insulation, the DC outputs of said rectifying circuits being series-connected.

13. The DC source of claim 12, wherein said transmitting means is grounded to said housing.

Claims

1. A device for providing a high DC potential between an element and ground, comprising: microwave generator means; waveguide means fed by said generator means; a plurality of modules electrically insulated from each other, each said module having a microwave receiving antenna and a rectifier connected thereto; means for electrically interconnecting the DC outputs of each said rectifier in a series-aiding relationship; a plurality of transmitting antennae fed by said waveguide means respectively coupled with corresponding ones of said microwave receiving antennae and being positioned at a distance therefrom sufficient to provide electrical insulation; and means for grounding said generator means, waveguide means, transmitting antennae and one of the DC outputs of a first one of said modules.

2. A device according to claim 13, wherein said microwave generator means includes a plurality of microwave generators and said waveguide means includes a plurality of waveguides fed respectively by said generators, each said transmitting antenna being supplied by a separate respective one of said waveguides

3. A device according to claim 1, wherein the microwave generator means is a magnetron oscillator.

4. A device according to claim 1, including additional means for supplying electric power to said element, said means comprising an additional receiving antenna carried by the element and coupled to a transmitting antenna which is supplied by a waveguide from an additional microwave generator.

5. A device according to claim 1, further comprising a grounded bell-housing containing a di-electric gas in which said modules are operatively positioned, said transmitting antennae being mounted on said bell-housing and said microwave generator means being external to said bell-housing.

6. A device for providing a large DC potential difference comprising : a microwave generator ; a wave guide fed by said generator ; a plurality of directional transmitting antennae coupled to said wave guide ; and a plurality of modules each having a directional receiving antenna confronting a respective one of said transmitting antennae and spaced therefrom and rectifier means receiving energy from the receiving antenna, the outputs of the rectifiers of all modules being connected in series, said generator, waveguide and transmitting antennae being at the same DC potential.

8. A device for providing a high DC potential between an element and ground, comprising: microwave generator means; waveguide means fed by said generator means; a plurality of modules electrically insulated from each other, each module having a microwave receiving antenna and a rectifier connected thereto; means for electrically interconnecting the DC outputs of each said rectifier in series-aiding relation; a plurality of transmitting antennae fed by said waveguide means respectively coupled with corresponding ones of said microwave receiving antennae and being positioned at a distance therefrom sufficient to provide electrical insulation; means responsive to the highest DC output potential of said modules with respect to ground for attenuating the poWer fed to said transmitting antennae via said waveguide means; and means for grounding said generator means, waveguide means, transmitting antennae and one of the DC outputs of a first one of said modules.

9. A device for providing a high DC potential between an element and ground, comprising: microwave generator means; means for modulating the microwave output of said generator means at a frequency lower than the frequency of the microwave output; waveguide means fed by said generator means; a plurality of modules electrically insulated from each other, each module having a microwave receiving antenna, a detection circuit for producing an output at the modulating frequency and a rectifier operatively receiving the output of said detection circuit; means for electrically interconnecting the DC outputs of said rectifiers in a series-aiding relationship; a plurality of transmitting antennae fed by said waveguide means respectively coupled with corresponding ones of said microwave receiving antennae and being positioned at a distance therefrom sufficient to provide electrical insulation; and means for grounding said generator means, waveguide means, transmitting antennae and one of the DC outputs of a first one of said modules.

11. A device according to claim 10, wherein each said module includes a circuit which serves to chop the voltage supplied by said detection circuit and drives the primary winding of said voltage step-up transformer which supplies said rectifier.