CA1039797A - Electron beam electrical power transmission system - Google Patents

Electron beam electrical power transmission system

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Publication number
CA1039797A
CA1039797A CA207,199A CA207199A CA1039797A CA 1039797 A CA1039797 A CA 1039797A CA 207199 A CA207199 A CA 207199A CA 1039797 A CA1039797 A CA 1039797A
Authority
CA
Canada
Prior art keywords
electron
current
radio frequency
path
potential
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA207,199A
Other languages
French (fr)
Inventor
Robert S. Symons
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Varian Medical Systems Inc
Original Assignee
Varian Associates Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US38991473 priority Critical patent/US3886399A/en
Application filed by Varian Associates Inc filed Critical Varian Associates Inc
Application granted granted Critical
Publication of CA1039797A publication Critical patent/CA1039797A/en
Expired legal-status Critical Current

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Classifications

    • GPHYSICS
    • G21NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21KTECHNIQUES FOR HANDLING PARTICLES OR IONISING RADIATION NOT OTHERWISE PROVIDED FOR; IRRADIATION DEVICES; GAMMA RAY OR X-RAY MICROSCOPES
    • G21K1/00Arrangements for handling particles or ionising radiation, e.g. focusing or moderating
    • G21K1/08Deviation, concentration or focusing of the beam by electric or magnetic means
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02Electrodes; Magnetic control means; Screens
    • H01J23/027Collectors
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J23/00Details of transit-time tubes of the types covered by group H01J25/00
    • H01J23/02Electrodes; Magnetic control means; Screens
    • H01J23/06Electron or ion guns
    • H01J23/065Electron or ion guns producing a solid cylindrical beam
    • HELECTRICITY
    • H01BASIC ELECTRIC ELEMENTS
    • H01JELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J25/00Transit-time tubes, e.g. klystrons, travelling-wave tubes, magnetrons
    • H01J25/02Tubes with electron stream modulated in velocity or density in a modulator zone and thereafter giving up energy in an inducing zone, the zones being associated with one or more resonators
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02NELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
    • H02N3/00Generators in which thermal or kinetic energy is converted into electrical energy by ionisation of a fluid and removal of the charge therefrom
    • HELECTRICITY
    • H05ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05HPLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H9/00Linear accelerators

Abstract

Electrical power is transmitted from a transmitting location to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting location and the receiving location. The beam is magnetically focused within the evacuated pipe. Electrical power to be transmitted is put into the beam in the form of kinetic energy by accelerating the beam to a high kinetic energy. The kinetic energy is extracted from the beam at the receiving location and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is extracted from the beam by collecting the beam current at a potential substantially equal to the potential of the source of the electrons, i.e. cathode potential, and causing the collected beam current to flow through the load to develop the depressed collector potential. In another embodiment, radio frequency accelerator means are utilized for r.f. current density modulating and accelerating the beam. The radio frequency current modulation on the beam is extracted at the receiving end by means of radio frequency circuits coupled to the beam. The extracted radio frequency energy is rectified for application to the load. In another embodiment, AC power at conventional AC power frequencies, as of 60 Hertz, is extracted from the beam by sequentially directing the beam into a plurality of depressed collectors coupled to respective primary windings of power transformers for deriving AC output power for application to a load.

Description

1039797 ~ -BACKGROUND OF THE INVENTION
The present invention relates in general to electrical power trans-mission systems utilizing an electron beam as the power transmitting medium and, particularly, to improved means for imparting kinetic energy to an electron beam and for extracting the kinetic energy from the beam at a remote location.
DESCRIPTION OF THE PRIOR ART
.
Heretofore, it has been proposed to transmit vast quantities of electrical power from a transmitting location to a remote receiving location -10 by means aE an electron beam traveling within an evacuated magnetically shielded pipe or cable employing "strong" magnetic focusing along the pipe to prevent unwanted beam interception by the walls of the pipe, Such a system iB disclosed in U.S. Patent 2,953,750 issued September 20, 1960.
In this prior proposed scheme, it was contemplated that kinetic energy would be imparted to the beam at the sending end by accelerating the beam to a high kinetic energy, as of 100 MeV, by a modified betatron type induction accelerator machine. In the modified betatron, the beam, while magnetically contained within a helical magnetic cable (pipe), was caused to pass through a plurality of accelerating gaps for increasing the kinetic 20 energy of the beam in a steplike fashion. That is, the accelerating electrical field, produced across the respective gaps by an AC potential applied in synchronism with pulses of the beam, caused the beam to be accelerated to the high output kinetic energy. It was contemplated that the high energy pulses of beam current could be at AC power frequencies of 25 or 60 Hert7 or, as an alternative, the pulse repetition rate could be in the radio fre-quency range by utili~ing a radio frequency cavity resonator at each of the accelerating gaps in the helical cable.
The kinetic energy of the high energy pulses of beam current was extracted at the receiving end by means of a~ reverse type accelerator which 30 decelerated the beam pulses in accordance with the amount of power de~
manded by the load. The decelerated (unuæed) pulses of beam current were returned to the sending end by meanæ of return magnetic cables or pipes ~ . .
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1~39797 connected back to appropriate ones of the electron beam accelerating machines. The returning beam pulses were 180 out of phase with the transmitted pulses of beam current leaving the machine. In this manner the unused energy of the beam was returned to the betatron accelerating machine.
It was concluded, in the above cited prior patent, that the radio frequency alternative was not feasible for transmitting relatively large amounts of power. On the other hand a problem with the use of magnetic induction accelerators operating even at conventional power frequencies is 10 that a vast amount of iron must be used causing attendant iron los~es due to hysteresis effecte.
SllMMARY OF THE PRESENT INVENTION
The principal object of the present invention is the provision of an improved electrical power transmission system employing an electron beam as the power transmission medium.
In one feature of the present invention, kinetic energy is imparted to the beam at the transmitting end of the power transmi sion system and is extracted from the beam at the receiving end by decelerating and collecting ~f the electrons of the beam at nearly zero velocity, whereby the kinet~ energy 20 of the beam is efficiently converted to electrical potential energy.
In another feature of the present invention, a magnet beam ocus structure, of eîther the permanent magnet or electromagnet type, is disposed ~urrounding the vacuum envelope containing the beam, and the beam focus magnet~ are surrounded by a magnetic shield, whereby the magnet structure i~ disposed outside of the vacuum envelope containing the beam such a~ to minimize outgassing problems and contamination of the vacuum containing the beam.
In another feature of the present invention, a magnetic beam focus- -ing transition section is provided at the power transmission location for 30 gradually increasing the intensity of the beam focus magnetic fields in the direction of electron flow from the cathode emitter to minimize undesired ~ -perturbation of the electron beam.

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1()39797 In another feature of the present invention, the magnetic beam focus structure includes a beam entrance transition section having an astigmatic -~
plural pole magnetic lens for providing a smooth transition of the electron flow into the main portion of the beam focus structure, to avoid undesired perturbation of the electron beam flow.
In another feature of the present invention, beam current collected at the receiving location is returned to the transmitting location via the pipe containing the beam, whereby the return current path is symmetrical relative to the beam path to prevent magnetic defocusing of the beam.
In another feature of the present invention, a D. C. beam acceler.~ -ating structure is employed at the transmitting end, such D. C. beam accelerating structure comprising a sequence of beam accelerating electrodes operating at sequentially higher beam accelerating potentials such as to produce a D. C. beam accelerating field in the beam path for accelerating , the beam to a high energy, whereby a relatively simple, inexpensive and efficient beam accelerator is obtained.
In another feature of the present invention, a D. C. beam decelerator structure is provided at the receiving end of the electrical power transmis-sion system, whereby the high kinetic energy electron beam is caused to ,' 20 pass through a series of beam decelerating electrodes 9equentially operated at lower potentials for decelerating the beam without intercepting a ~ub-stantial percentage of the high velocity electrons on the decelerating structure.
The kinetic energy of the beam is thereby efficiently converted into D. C. ;
' potential energy.
In another feature of the present invention, kinetic energy is imparted to the beam at the transmitting end by passing the beam through a radio frequency accelerator. Radio frequency wave energy is extracted from , the beam at the receiving end or tapped off in intermediate locations by means of a receiving radio fr~quency wave supportive structure excited by the RF energy imparted to the beam at the transmitting end. Rectifiers are coupled to the receiving radio frequency structure for converting the radio frequency energy to D. C. power for application to the load.
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~039797 In another feature of the present invention, radio frequ~ncy reso-nators are periodically spaced along the beam path intermediate the trans-mitting and receiving ends for rebunching the beam to counteract space charge debunching effects.
In another feature of the present invention, a contrbl circuit is provided for monitoring the power demanded by the load at the receiving end of the transmission system and for causing the power transmitted to be equal to the power demanded at the receiving end.
In another feature of the present invention, the beam power trans-10 mitted from the transmitter end to the receiver end is pulsed into a train of pulses, each having a duration shorter than the time required to form ~; -sufficient ions to fully neutralize the beam space charge, with successive pulses being separated by a short time for ion drainage during which time po~itive ions are drained to the walls of the envelope.
In another feature of the present invention, ion draining electrodes are disposed along the beam path for collecting and draining positive ions. ;
In another feature of the present invention, a plurality of beam collector structures are provided at the receiving end of the transmission system and a beam deflector is provided for sequentially deflecting the 20 beam into respective ones of the beam collector structures for supplying alternating current to the load.
In another feature of the present invention, a pl~rality of electron guns are energized with alternating beam voltage at the transmitting end of the power tran3mission system and a beam deflector is provided at the ;
transmitting end for sequentially directing the current from respective ones of the electron guns into a common beam path leading to the receiving end, whereby A. C. power at the transmitting end is efficiently rectified into ;; direct beam power for transmission to the receiving end.
In another feature of the present invention the beam current is 30 pulse-modulated for control of the average electrical power transmitted to the receiving location.

In another feature of the present invention, radio frequency load means are coupled in RF wave energy exchanging relation with the interior of the evacuated beam pipe for coupling to and suppressing undesired modes of wave energy propagation within the pipe.
In another feature of the present invention the period of a periodic beam focus magnet structure is varied randomly to avoid undesired cumu-lative radio frequency wave-beam interactions, whereby undesired oscilla-tions are avoided.
More particularly, there is provided in an electron beam power transmission system for transmitting electrical power from a transmitting location to a receiving location geographically removed from the transmitting location: elongated evacuated envelope means extending from the transmitting location to the receiving location; transmitter means at the transmitting location for forming, accelerating and projecting a beam of electrons over an elongated beam path extending within and along said evacuated envelope from the transmitting location to the receiving location; and receiver means at the receiving location for converting the kinetic energy of the beam to ~j electrical power for application to a power load, comprising, means for il decelerating the electrons by an electric field component in the direction of i 20 their motion and means for collecting the decelerated electrons as conduction curr ent .
Other features and advantages of the present invention will become apparent upon a perusal of the following specification taken in connection with the accompanying drawings wherein:
BRIEF DESCRIPTIGN OF THE DRAWINGS ;;
Fig. 1 ifl a schematic longitudinal sectional foreshortened view, ~ partly in block diagram form, of an electron beam power transrni~sion J s5r~tem incorporating features of the present invention.
Fig. lA is a sectional view of the structure of Fig. 1 taken along line lA-lA in the direction of the arrows.
Fig. 2 is an enlarged sectional view of a portion of the structure ` of Fig. 1 taken along line 2-2 in the direction of the arrows.

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~;~397g7 Fig. 2A is a view similar to that of Fig. 2 showing an alternative embodiment of the present invention.
Fig. 3 is an enlarged schematic detail view of a portion of the structure of Fig, 1 delineated by line 3-3.
Fig. 4 is a schematic longitudinal sectional view of a portion of Fig. 1 delineated by line 4-4.
Fig. 5 is a view similar to that of Fig. 1 depicting an alternative embodiment of the present invention.
Fig. 6 is a schematic circuit diagram of the winding portion of the 10 transformers of the circuit of Figo 5 delineated by line 6-6.
Fig. 7 is a schematic circuit diagram of the winding portions of the transformers of Fig. 5 delineated by lines 7-7.
Fig. 8 is a transverse sectional view of a portion of the structure of Fig. 5 taken along line 8-8 in the direction of the arrows.
Fig. 9 is a schematic diagram, partly in block diagram form, of an electron beam power transmission system incorporating alternative ~ ~;
embodiments of the preRent invention.
.: .
Fig. 10 are waveforms of beam voltage, beam current, and grid voltage for an electron beam power transmission system employing an ~-~
20 interrupted beam .
Fig. 11 i8 a schematic line diagram of an electron beam power transmission system employing alternative feature~ of the pre~ent invention.
Fig. 12 is a schematic line diagram of a power transmission system employing alternative embodiments of the present invention.
Fig. 13 is a schematic line diagram of an alternative embodiment to a portion of the structure of Fig. 11 delineated by line 13-13.
Fig. 14 is a schematic circuit diagram for an electrical power transmission system incorporating features of the present invention and depicting an alternative embodiment.
Fig. 15 is a plot of current and voltage waveforms for one phase ~ ~ -of the power transmission system of Fig. 14. ~

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lQ3g797 Fig. 16 is a view similar to that of Fig. 1 depicting an alternative embodiment of the present invention.
Fig. 17 is a schematic circuit diagram, partly in block diagram form, of a control circuit useful in a power transmission system of the present invention.
Fig. 18 is a view similar to that of Fig. 17 depicting an alternative embodiment of the present invention, and ~
Fig. 19 is a schematic circuit diagram, in block form, of the -comparator circuit useful in the en~bo~ment of Figs. 17 and 18.
DESCRIPTION OF ~$ ~EFERRED EMBODIMENTS -Figs. 1 and 2 show an electron beam power transmission system 11 incorporating features of the present invention. System 11 includes an electron gun 12 and a DC beam accelerator section 13 at the power trans~
mitting end 14 of an elongated evacuated envelope 15 which extends for a ~ubstantial distance, e. g. 0.1 to 1,000 miles, to a remote power receiving -location 16 at the receiving end of the transmission system lo At the receiving location 16, an electron beam collector structure 17 is connected to the evacuated envelope 15 by a DC beam decelerating section 18.
`I Briefly, electron gun 12 serves to form, accelerate and project a 20 beam of electrons 19 into the beam accelerator section 13 which accelerates the beam to a very high energy, as of in excess of 0. 1 million electron volts MeV, and preferably in excess of 0, 5 MeV. ~ this manner, substantial kinetic energy is imparted to the electron beam.
Although a separate accelerator section 13 i8 employed in the ! embodiment of Fig. 1, this is not a requirement. If the beam voltage is below 0. 25 MeV, the anode of the gun 12 may be operated at 0. 25 MeV for accelerating the beam up to 0. 25 MeV. Actually the accelerating section 13 can be considered as part of the anode structure of the gun 12.
The beam 19 is then projected axially into the elongated envelope 15.
30 The beam is magnetically confined in envelope 15 by a quadrupole magnetic ' beam focus structure 22 to avoid substantial interception on the walls of the evacuated envelope, An astigmatic magnetic lens system 21 (see Figs. 1 :.:

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- ` -and lA) is provided between the accelerating section 13 and the entrance to the elongated envelope 15 to provide a smooth magnetic focusing transition of the electron stream from the accelerator into the quadrupole beam focus field in envelope 15.
The magnetic lens system 21 comprises one or more quadrupole lenses. Each quadrupole lens includes four magnetic poles of alternating polarity around the envelope 15 which are energized by electric coils 10 wound around the poles 9. A tubular magnetic shield 20 surrounds the ~- poles 9.
The quadrupole magnetic beam focus structure 22, more fully described below, spirals around envelope 15 to provide "strong" magnetic beam focusing of the type described in the aforecited U.S. Patent 2,953,750.
The envelope 15 is evacuated by means of a plurality of glow discharge getter-ion vacuum pumps 23 or any other suitable vacuum pump disposed at suitable intervals along the pipe 15 in gas communication therewith for evacuating same to a relatively low pressure as of 10-7 torr. Thus a beam can be transmitted for hundreds of miles through tubular envelope 15 without substantial 10BS of energy.
~ ~ As an alternative to the use of the quadrupole lens 21, the quadru-pole beam focus structure 22 i8 extended into a transition region between the cathode 31 of the gun 12 and the entrance to pipe 15. In this transition region, the quadrupole beam focus magnetic field intensity in the beam path gradually increases in strength from zero to its full value at the entrance to the main portion of the pipe 15 (see Fig. 13).
At the power receiving location 16, the beam is decelerated by a beam decelerator section 18 to a potential as close as possible to the potential of the source of electrons within the gun 12, thereby converting the kinetic energy in the beam to potential electrical ener~y. The electrons of the beam, having low velocity (i.e. within 5% of the collector potential)? are collected on the interior walls of the beam collector structure 17, which -operates close to the potential of the source of electrons within the gun 12, whereby the beam energy converted to heat in beam collector 17 is minimized.
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The collected beam current is caused to flow through an inverter load 24 to the Vdcuum envelope 15, typically at local ground potential. The collected beam current is returned to the transmitting location 14 via the ~, electrically conductive walls of the envelope 15. The inverter 24 inverts the DC power to three phase AC output power which is supplied on output lines 25, 26 and 27. ln a typical example, the beam 19 has a current of 1,000 amps and is accelerated by the accelerator section 13 to a potential of one million volts, such that the power transmitted by the beam from transmitting location 14 to receiving location 16 is 1 gigawatt.
A control circuit 28, as more fully disclosed below with regard to Figs. 17-19, monitors the potential Vc of the beam collector 17 and com~
pares it with the potential Vk of the source of electrons to derive an error ~-signal for controlling the beam current via a control electrode Z9 in the electron gun 12 or adjustment of Vk, such that the power transmitted to the ~ ~
. . ~.
receiving end 16 is regulated to match the demand for power at the receiving end 16. ;
The electron gun 12 includes a spherically concave thermionic cathode emitter 31 of sufficient area to emit the required electron current, . .. .
~uch as 1,000 amps. Cathode emitter 31 is heated to thermionic emission 20 temperature by means of a filamentary heater 32. Operating power is supplied to the filamentary heater 32 from a power ~upply 33. A focus electrode 34 surrounds the peripheral edge of cathode emitter 31 to aid in shaping the electron beam in the region of cathode emitter 31.
The control grid 29 is preferably of the type protected by a shadow grid wherein the shadow grid structure, operating at substantially cathode potential, i8 dispo~ed immediately adjacent the surface of the cathode emitter 31 and the control grid has apertures aligned with the apertures in the shadow .
grid. AB an alternative to a control grid, a modulating anode may be em-ployed as the control electrode 29.
The cathode emitter 31 is preferably dimpled, with the dimples having a lesser radius of curvature than that of the composite cathode emitter ~ ~ -surface. The individual dimples in the cathode serve as separate cathode ..
. ~ , - 1 1 -emitters for individual electron beamlets passing through the aligned open-ings in the shadow and control grid structures in a substantially non-intercepting manner. Such an electron gun and control grid structure is disclosed and claimed in U.S. Patent 3,558,967, issued January 26, 1971, ~;
and assigned to same assignee as the present invention.
In a typical example, thermionic cathode emitter 31 comprises an impregnated tungsten matrix cathode approximately 15 cm. in diameter and having an area of approximately 350 cm2. At 1,000 amperes, such a cathode would operate at a current density of approximately 3 amperes per square centimeter. Tunsten matrix cathodes, impregnated with barium aluminate, can operate continuously for five Srears at this current density.
The beam accelerator section 13 is preferably of the type used with the Van de Graaff or Cockroft-Walton generators and is disclosed in an arti-le entitled "El~ectrostatic Generator~ for the ~cceleration of Charged Particles" appearing in Reports on Progress in Physics, Vol. 11:1-18 (1948).
Briefly, this type of accelerator includes a sequence of generally planar centrally apertured plate shaped electrodes 35 wherein the accelerating potential, as of 0.1 to 5 million volts, is evenly distributed among a number of the accelerating electrodes 35. A potential divider 36 employs a string ', 20 of resistors to divide the beam potential Vb for application of respectively increasing potentials to the respective ones of the accelerating electrodes 35.
~he potential difference between successive electrodes 35 in the accelerator section 13 i9 prei~erably le~s than 200 kilovolts to prevent arcing between the adjacent electrode~ 35.
Electrodes 35 serve to provide a uniform beam accelerating electric field within the beam path 19; the first few ones of electrodes 35 near the upstream end of the beam path 19 serve to focus and to converge the electron ~tr~m. Dn a typic~l e~mple, the b~m would ~- convert~d from a dl~meter of 15 cn~. at cathode emitter 31 to approximately a diameter of 5 cm. at the ~ -output end of accelerator section 13. ~ -'~ A three phase rectifier 38 receives the three phase input power from a power generator or the like and rectifies this three phase input to produce direct output current at a high negatîve cathode voltage Vk, as of -0.1 million ` ~, volts to -5 million volts.
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10397~7 ::
Fig~ 2 shows, in section, the evacuated envelope 15 andbeam focus structure 22. More particularly, evacuated envelope 15 comprises a pipe made of an electrically conductive material, as of aluminum. In a preferred embodiment, the pipe also serves as the return electrical con-ductor of the power transmission system 1 such that the collected beam current flows back to the power supply of the electron gun 12 through a return path which is symmetrical relative to ~he beam 19. In this manner, undesired magnetic defocusing of the beam by the magnetic field of the beam current loop is avoided. In the preferred embodiment, the pipe 15 is 10 electrical~y insulated from earth Ruch as by the ferrite permanent magnets 22. In a typical example, aluminum pipe 15 has a diameter of approxi- -mately 10 cm. and a wall thickness of approximately 3 mm.
The beam focus permanent magnets 22 are disposed around pipe 15 at 90 spacing for a quadrupole type of "strong" magnetic focusing. In "strong" magnetic beam focusing a quadrupole magnetic field is provided which has flux lines which lie in planes almost perpendicular to the direction of the beam. The flux lines are made to rotate about the beam by spiraling permanent magnets 22 around pipe 15. The permanent magnets are radially polarized, with the magnetic pole~ alternating in polarity in the circum-ferential direction around the pipe 15. Although the preferred embodiment utilizes a quadrupole magnetic structure, other multiple pole t3tructures may also be used, such a~ 6, 8, 10 or 12 poles etc. Also other type of magnetic focu~ing may be employed such as a series of discrete magnetic lenses or a confining magnetic field.
As an alternative to the use of permanent magnets for producing the beam focus magnetic field, electromagnets are employed. The e~ectro-magnetic equivalent is useful where operating temperatures are encountered . "
which are outside of the rated operating temperature range of the permanent magnet material. A quadrupole electromagnetic beam focus struci~ure comprises four conductors 40 ~piraling around the pipe 15 in 90 circum-ferentially spaced relation (see Fig. 2A), and energized with direct current of opposite direction in adjacent conductors 40.
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:~039797 An electron traveling parallel to the beam path 19 will interact with a magnetic vector at right angles to its direction of travel. The field has a strength proportional to the distance between the electron and the axis of the beam path. The magnetic vect~r rotates in a direction around the pipe at twice the rate of the quadrupole rotation. The magnetic vector will cause the electrons to follow helical paths. The magnetic focusing force of the quadrupole field on the electron, when the electron is far from the axis, is larger than the defocusing force when the electron is near the axis. As a result, there is a net time averaged inward focusing force.
In this kind of focusing, the magnetic field need only provide a focusing force that is sufficient to compensate for the difference between the space charge forces, which tend to defocus the beam, and the beam self focusing magnetic field. The problem of focusing the beam is less severe at high beam voltage since the space charge forceA are reduced at a given current flow and the self magnetic field of the beam tends to compensate the space charge repulsion. This means that smaller focusing fields can be used to confine the beam. For example, at one million volts~ 8/9 of the space charge force is neutralized by the self-magnetic field of the beam -current. Since the focusing force is proportional to the distance of the 20 electron from the axis of the pipe 15, the beam will tend to follow the center of pipe 15 even if the pipe has curvature.
Magnetic focusing results in ion trapping, which leads to plasma instability. Residual gas molecules within the pipe, when struck by electrons produce positive ions which are attracted toward the center of the beam.
The positive ions in the center of the beam tend to neutralize the space charge repulsion, causing the beam to condense toward the center. Therefore, ion drainage or neutrali7ation is required. The simplest way to obtain ion neutralization is to turn off the beam perio~Elically for a few microseconds to allow the ions to move to the wall of the pipe 15, where their charge will 30 be lost. The time required for ion neutralization of the beam at a pressure of 10-7 torr at an electron energy of 1 megavolt is about 5 milliseconds. ~ -Thus, the beam is turned off by means of grid 29 every few hundred micro ~

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1~)39797 :
seconds, for a few microseconds, causing any ions that have formed to mutually repel each other and drain to the wall. As an alternative, (shown in Fig. 3) insulated negative electrodes may be provided at suitable spacings along and within the pipe 15 for generation of periodic electric fields (potential wells) for drawing the ions to the electrodes. More particularly, each ion drain may include an enlarged diameter section of the pipe 15" to provide an annular recess to receive a metallic ring shaped drain electrode 1 supported from a conductive post 2 via a feedthrough insulator 3. The post 2 is connected to source of negative potential 4, as of -100 to -1000 V, 10 for collecting and draining positive ions from within the pipe 15. Various suitable ion draining electrodes and schemes are disclosed in U.S. Patent
2, 963, 605 is sued December 6, 1970.
In a preferred embodiment, the permanent magnets 22 are made of grain oriented ferrite particles with a BH product of nearly 4 million gauss-oersteds. Such a material i commercially available at 2,000 gauss and ~ -2, 000 oersteds in which the ferrite particles are bonded in a flexible plastic 80 that half of the energy product of the oriented ferrite is sacrificed for the ~ ~1 ~' convenience of flexible plastic bonding. Such a material has sufficient magnetic energy for this application. This material is also relatively in-20 expensive in large quantity. Any other permanent magnetic material might be substituted.
For a permanent magnet focus system capable of focusing, for example, a one megavolt, one thousand ampere beam, the energy stored in the focusing field is 0. 69 joule per meter of length; therefore, 16, 000 cubic !
~l inches of one million gauss-oersted magnetic material per mile of line length would be required. The magnets 22 are placed external to the vacuum envelope 15 80 as not to contaminate the vacuum. A tubular magnetic shield 41 surrounds magnets 22. In a typical example, the magnetic shield 41 may comprise a spiral wound soft iron tape 0. 010 inch thick. The focusing ~` 30 magnetic field required in~ide of the pipe 15 for focusing the beam is in the range of 100 to 200 gaussO

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The vacuum envelope 15 is evacuated by a plurality of glow dis--charge getter ion vacuum pumps, such as VacIon~pumps commercially available from Varian Associates of Palo Alto, Cal. These pumps have no moving parts, produce extremely clean vacuums free from any oil contami-nation and consume very small amounts of power when pumping on a closed system. In addition, these pumps have very long life under these conditions.
Approximately eighteen 8-liter per second vacuum pumps 23 are required for each mile of length of the pipe 15. Such a vacuum system would consume approximately 0. 54 watt per mile (3000 volts at 180 microamperes).
Under certain operating value~ of beam voltage and current and as ~ ;
a function of the diameter and le~th of the pipe 15, microwave electro-. . : . .
magnetic interaction may be obtained between space charge waves of the ;
beam 19 and microwave energy propagating within the pipe 15. This results in undesired velocity and current modulation of the beam as well as the generation of undesired amounts of microwave energy within the pipe 15. ;
Accordingly (See Fig. 4), wave traps 5 or other means of coupling a lossv : .
material to the microwave electromagnetic fields within the pipe 15 are : . , located along the pipe for absorbing the undesired microwave energy to damp , . . .
out undesired microwave oscillations. In a typical mode trap 5, an evacu-20 ated chamber 6 containing an array of resistive card wave energy absorbers7 is coupled to the microwave fields of the pipe 15 via a suitable coupling 310t or hole 8. As an alternative, the inside wall of the pipe 15 ma~r be coated with a lossy coating of a lossy alloy of Al, Fe and Co, such as Kanthal~).
As another alternative, the pitch of the spiraling quadrupole beam focus magnet structure i~ varied bv, for example, + 20% in a random way to avoid cumulative fast wave beam-field interactions and their resulting o 8 c illation 8 .
At the receiving location 16 the beam decelerating section 18, 30 similar to the beam accelerator section 13 except turned end-for-end, serves to decelerate the ~eam to a beam voltage a~ close as possible to the ; voltage of the cathode emitter 31, namely, Vk without reflecting beam current to the decelerator section 18. -.. . .:

The decelerated beam is received within the depressed beam col-lector structure 17; the collector operates at a potential Vc.approximately equal to the decelerated beam or source potential Vko In a preferred embodiment, the depressed collector structure 17 is of the type disclosed and claimed in U.S. Pat. 3,453,48Z issued 1 July 1969 assigned to the same assignee as the present invention, and preferably includes the improvement of a center spike. The depressed collectors of this type are very efficient - and operate with beam collecting efficiencies of 98%, i.e., only 2% of the transmitted power is lost in the collector 17. However, in a one gigawatt - 10 transmission system with 98% beam recovery, there is still 20 megawatts of power which must be dissipated in the collector 17.
The collector 17 is preferably of the water or liquid cooled type disclosed in U.S. Pats. 3,374,523 issued 26 March 1968 and 3,414,757 issued 3 December 1968 and assigned to the same assignee as the present invention. The collector should be scaled in size such that the power dissipation on the interior surfaces thereof results in a power density of i below one kilowatt per square centimeter.
One main advantage of the electrical power transmission system 11 ~ of the present invention is that it provides means for transmitting a gigawatt 20 quantity of electrical power at relatively low cost per mile and low loss.
This is because of the elimination of high voltage, the source of most of the problems in conventional transmission lines, from the main portion of the line. Energy is transmitted in~tead in kinetic form by means of a beam of electrons. The high energy electron beam is launched, transmitted through evacuated pipe 15 and recovered with losses low enough to be competitive with conventional overhead high voltage transmission lines. The economic savings in right-of-way cost and ecological advantages of less ozone genera-tion and elimination of un~ightly towers or excavations in either underground f~ or above ground installations justify its use. Pipe 15 may be installed 30 underground in a ditch or, for above ground systems, can simply lie on the surface or be supported by bents, a catenary, or existing bridge structures. ~-11~39797 Figs. 5-8 show a polyphase electric power transmission system 42 similar to that previously described with regard to Figs. 1-2 with the exception that the rectification and inversion functions have been combined with the transmission system. More particularly, six separate electron guns 12 and their respective beam accelerator sections 13 are disposed at the transmitting location 14 for projecting six separate electron beams into respective pipes 15'. Each pipe is magnetically shielded and provides "strong" magnetic focusing and converges toward the common m~gnetically shielded and magnetic focused pipe 15 leading to the receiving location 16.
10 A magnetic deflection yoke 43 is provided at the confluence of the respective beam input pipes 15', at the transmitting location 14, for sequentially and selectively deflecting the electron beams for respective ones of the electron guns 12 into common pipe 15. ;~
Similarly, at the receiving location 16 the main transmission pipe ~ i;
15 splits into six separate pipes 15' each leading to a respective beam decelerator section 18 and a depressed collector 17. A magnetic deflection yoke 44 is provided for sequentially deflecting the output electron beam into respective ones of the output pipes 15'. Deflection yokes 43 and 44 are of the conventional type used in cathode-ray tubes or in accelerator-to-target 20 deflection systems of high energy particle accelerating machines such as at the Stanford Linear Accelerator Center at Stanford, Cal.
Input power to be transmitted to the receiving location 16 is supplied to the transmitting location 14 from a suitable generator, not shown. The three phase input power is applied to the primary windings 45 of an input transformer 46. The primary windings 45 are connected in the delta con-figuration as shown in Fig0 6 and the secondary windings 47 of the input transformer 46, as shown in Fig. 7, are each center-tapped at ground or Vb potential and wound in a 6 phase configuration. The opposite ends of the center-tapped windings 47 are coupled to the cathode emitters of each of the .... ,., .. ~ :: , 30 pair of guns lZ for a respective phase of the three phase transmicsion system. For example, for the A phase, one end of the center-tapped winding 47 is coupled to one gun and the other end of the center-tapped winding 47 is f~ :. :
~ - 18 _ ~-1(~39797 coupled to the other gun. Due to the seIf rectification characteristic of the thermionic diodes, each of the guns of a particular phase would, in the absence of a control electrode 29, conduct only during one-half of the cycle, such conduction halves being 180 out of phase with respect to each other.
Control signals are applied to the control grids 29 via modulators 48 for limiting the beam conduction phase angle for each gun 12. More particularly, the conduction phase angle is limited to a first approximation to 3260 where p is the number of phases for the polyphase transmission system 42. In the case of a three phase system utili7ing six electron guns, i~
10 the beam conduction angle for each of the guns is limited to 60, and would normally be centered on the time when the applied voltage is a maximum.
The operation of the magnetic deflection yoke 43 is synchroni~ed with the potentials applied to each of the respective guns via leads 49 which feed into a deflection control circuit 51 and which serve to synchroni~e the input and output beam deflectors 43 and 44, respectively, such that the beam current is directed into the proper beam collector 17.
At the power receiving location 16, each phase of the three phase system has its re~pective pair of collectors connected to opposite ends of one of three center tapped primary windings 52 of an output transformer 53.
20 The secondary windings 54 of the output transformer 53 are connected in the delta configuration as shown in Fig, 6. ~n output voltage V& i~ ~en~ed across each of the re~pective phases of the output primary windings 52 via voltage sensors 55 (See Fig. 9) and these voltages are fed back to the gun modulators 48 to control the amount of the beam current drawn from each of the respective guns such that the power delivered to the load is equal to the power demanded by the load as rnore fully described below with regard to Figs. 17-19.
Due to the relatively short conduction phase angle for each of the electron guns and therefore the short phase angle for current delivered to 30 each of the respective collectors, the current pulses delivered to the pri-mary windings 52 of the output transformer 53 will be rich in harmonics of the power frequency.

1~)39797 : ~
However, the connection of the collectors 17 of each phase (three phase system) to opposite ends of each of the respective output primary windings 52 serves to cancel out the even harmonics of the power frequency (i.e. 60 H7). l~n addition, the balanced connection of the collectors 17 relative to the centertap in the output primary windings 52 serves to prevent ~ ~
undesired saturation effects of the transformer 53 due to the DC component ~ ~ -of current flowing through each primary winding 5Z. The third harmonic -~
and multiples thereof are effectively cancelled by using the delta connected secondary windings. The fifth, seventh, eleventh, thirteenth, etc. odd ~ -;
10 harmonics are bypassed by means of multiplicity of series resonant filters, such as filter 56, tuned for each respective odd harmonic and connected in ~hunt with the respective primary output winding 52. ;
The delta winding conneetion for caneelling of the third harmonie and multiples thereof is only operative in a three phase system or multiples of a three phase system. Aeeordingly, in a single phase or two phase ~ystem series resonant bypas~ filters 56 are employed for each third harmonic or odd multiples thereof, such as 3rd, 9th, 15th, etc.
Typieally, the lowest harmonic will have the largest amplitude.
Thus, a fifth harmonic filter 56 may suffice dependent upon the shape of Z0 the beam current pulse. Also the beam current pulse is preferably shaped by a waveform shaping eireuit which shapes the eontrol electrode potential to reduee the fifth, seventh, eleventh, thirteenth, etc. har~onies of beam eurrent. Sueh a wave shaping eircuit is eontained within modulator circuit 48 and is operative upon the shape of the signal fed to control electrode 29.
For example, for a beam current pulse train as shown in Fig. 10, t'here is a eertain value of beam eonduction angle which will reduce any given harmonie of the pulse repetition frequeney of beam current to zero.
Thus, the wave ~haping cireuit eontrols the beam conduetion angle to mini-mize the eertain harmonic.
Eaeh of the primary windings 52 has a bypass capacitor 57 con-neeted in parallel with the inductance of each of the primary windings 52 for bypassing harmonies of higher order than those filtered by filters 56.

~ ',' ' Referring now to Fig. 9, there is shown an alternative electron beam power transmission system similar to that previously described with regard to Fig. 5 with the exception that a pair of magnetically shielded and magnetically focused pipes 15 are employed for each phase of the AC
power transmission system. For example, in a single phase system two pipes 15 are employed. The pair of electron guns 12 for each phase of the AC power transmission system are connected in 1~0 out of phase relation by connection of the cathode emitters 31 to opposite ends of a center tapped secondary winding 47 of the input transformer 46.
The advantage of the AC power transmission system of Fig. 9 is that the conduction phase angle can be increased to a value substantially in excess of the 60 conduction phase angle for the three phase system of Fig. 5. This reduces the harmonic content in the beam current supplied to the output transformer 53.
However, it is generally undesirable to employ the whole 180 beam conduction phase angle during each conductive half cycle of the applied alternating beam potential. The reason for this i8 that at relatively low values of beam voltage Vb, the electrons have relatively low velocities and thus correspondingly relatively long transit times through the pipe 15. In 20 such a~case, some overtaking of the slow electrons may be obtained by subsequent fast electrons. Thi~ has a deleterious effect upon the beam collector efficiency since, for high collector efficiency, all the electrons -: , ab a ~given instant in time should have the same velocity. Also, such over-taking will cause distortion of the current waveform, usually increasing the unwanted harmonic content thereof. Also, the beam focus ~ystem, depending upon the particular magnetic focusing scherne employed, may not properly focus electrons over wide ranges of electron velocities.
Therefore, it is preferred to limit the conduction of beam current to only a portion of the cycle of applied beam voltage corresponding to a 30 value of beam current greater than 1/6 of the peak or maximum be~
current, i. e. IMAX/6.

' J : . , 1039797 - ~ :~
Referring now to Fig. 10, there is shown the waveforms for beam . .
current Ib, beam voltage Vb and control electrode voltage VQl and VQ2.
The beam conduction angle is readily controlled by applying a fixed DC ~ j ;
negative bias voltage Va to each of the respective control electrodes 29 such that the beam conduction angle is limited to that portion of the cycle corres-ponding to a respective grid voltage exceeding the cathode voltage Vk. The -beam conduction angle can then be varied and controlled as desired by increasing or decreasing the magnitude of the dc negative grid bias voltage Va.
Returning again to Fig. 9, it is desirable to control the power factor . ,- -: .:
10 of the load as reflected into each of the primary windings 52 of the output transformer 53 such that the collected beam current Ic is in phase with the .. .
respective collector potential Vc. Accordingly, a continuously variable reactance, such as that provided by a synchronous condenser 58, is prefer-ably connected across each of the respective output delta connected secondary windings 54. A voltage is derived which is proportional to the collected beam current Ic. This voltage is derived from a current transformer 59 :
connected between the centertap of the primary winding 52 and the pipe 15~ :
This voltage is fed to one input of a phase comparator 60 for comparison with the phase of the respective collector voltage Vc as derived from sensor 20 55 to derive an error output which is fed to the field control of the synchron-ous condenser 58 for causing the condenser 58 to take the proper value of reactance to bring the beam collector current Ic into phase with the collector voltage Vc. The power factor control circuitry of Fig. 9 is also utilized to advantage in the system of Fig. 5.
Referring now to Fig. 11, there is shown an AC power transmission system similar to that of Fig. 9 wherein a common magnetically focused and magnetically shielded pipe 15 is employed for each phase of the AC power transmission system. More particularly, convergent and divergent pipes 15', as previously described with regard to Fig. 5, are employed at the 30 transmitting and receiving locations, respectively, for feeding the electron beams from the guns of each phase into the common pipe 15 and out of the common pipe to respective collectors of each phase. The deflection of the ~ . . .

i:l . . ..
_ 22 - ` `-: ~

beams at the transmitting and receiving locations is obtained by a deflection control circuit driving each of the deflecting magnets 43 and 44 in response to inputs derived from the respective gunsO The advantage of the systenn of Fig. 11 over that previously described with regard to Fig. 9 is that only one pipe 15 is required for each phase of the AC power transmission system.
Referring now to Fig. 13, there is shown an alternative embodi-ment to that portion of the structure of Fig. 11 delineated by line 13-13.
More particularly, the input deflection magnet 43 is replaced by "strong"
magnetically focused and convergent input pipes 151'. However, magnetic deflection is still required at the receiving location.
Referring now to Fig. 12, there is shown an alternative three phase power transmission system 59 incorporating alternative embodiments of the present invention. More particularly, the system is similar to that previously described with r8gard to Fig. 9 with the exception that only one pipe 15 is provided for each phase of a three phase system and collection of beam current through each phase of the three phase system occurs only once per cycle at the power frequency, as contrasted with twice per cycle at the power frequency as indicated in Fig. 10. The windings 47 and 52 have only three phases as contrasted with six phases as shown in Fig. 7.
The power transmission system 59 of Fig. 12 has the advantage of simplicity in that it provides only one pipc 15 per phase of the three pha~e sy~tem but it has the disadvantage that the harmonic content of the current delivered to the primary windings 52 of the output transformer is greater than that obtained in the system of Fig. 9.
Referring now to Figs. 14 and 15, there is shown an alternative multiple pipe polyphase A.C. transmission system 62. Transmission sy~tem 62 is similar to that of Fig. 5 with the exception that a pair of pipes 15 i8 provided for each phase of the polyphase system, as shown in the system of Fig. 9. In this system 62, the beam current through each of the pipes 15 does not have to be limited to 360/2p degrees of phase angle where p is the number of phases. In the case of a three phase system, the con-duction of current is preferably limited to a phase angle ~uch that the -~ ~''- :''' . : . - .... : .,. ~ . -. . ... . . . . - .. . . .

lQ39797 ` : ~
current conducted has a value greater than 1/6 Irnax, where Imax is the peak beam current for each phase. This means that current is conducted from each gun for approximately 120-140 of phase angle of the input voltage waveform, as shown in Fig. 10. This reduces the harmonic content in the current flowing in the primary windings 52 of the output transformer -53. One advantage of the system of Fig. 14 is that the filtering of undesired harmonics in the output of the transformer 53 is simplified at the expense of additional pipes 15. A second advantage is the elimination of the mag-netic deflectors 43 and 44.
. ...
A further advantage of the system of Fig. 14 is that the beam current return paths are separate~for each beam to preYent cross flow of beam return current flow with attendant potential differences between the various pipes 15 as encountered with unbalanced loads. However, the windings 47 and 52 are balanced in the transformers 46 and 53 to avoid D. C.
saturation of the transformer cores, i. e., bucking connected for beam current flow. ;
As an alternative to the sy~tem 62 of Fig. 14, the number of pipes 15 can be reduced to one per phase of the polyphase A. C. system by using a common pipe 15 per phase and employing the magnetic deflection system 20 of Fig. 11 for sequentially deflecting beams from respective pairs of gun~ ;
12 into and out of the respective common pipe 15. In this latter Yystem, the input magnetic deflection can be eliminated since the input magnetic pipes 15"
will focus the respective beams sufficiently to allow the individual beams to negotiate the bends in the pipes 15' at the confluence of the pipes 15 with the common pipe 15 as shown in Fig. 13.
Referring now to Fig. 16, there is shown an alternative transmission system 72 of the present invention. The power transmission system 72 of Fig. 16 is similar to that of the system of Fig. 1 with the exception that RF
, accelerator means 73 are employed for bunching and accelerating the beam 30 to re~tively high energies, for example, 100 ~IeV.
... .
The radio frequency accelerator 73 comprises a plurality of ~ -.
individual cavity resonators 74, as of 250 such cavities, sequentially ~ -J
-~ - 24 - -~0;~9797 arranged along the beam path 19 for successive electromagnetic interaction with the beam for velocity modulating the beam with RF energy at the resonant frequency of the resonators 74. In a typical example, the resona-tors 74 are of the folded half wavelength type as used in the accelerator at the National Accelerator Laboratory of Batavia, Illinois. Th~ resonators are tuned to a suitable radio frequency, as of 30 megahertz, and are driven in the proper phase relation from a 30 megahertz oscillator 75 via phase shifters 76 and power amplifiers 77. ~ -The power amplifiers 77 are preferably conventional tetrodes 10 providing high efficiency, i. e., greater than 90% in class C operation with small angl~ of current flow and possibly third harmonic squaring of the plate voltage. Phase-locked magnetron oscillators could also be utilized as a source of microwave energy for driving the cavities 74, but a lower frequency has the further advantage of decreasing debunching effects due to both velocity spread and space charge effects.
For a finite beam of small diameter in pipe 15, the longitudinal plasma frequency is proportional to the driving frequency. The plasma frequency for a 30 megahertz driving frequency is about 2,000 hertz for a 10 ampere, 100 megavolt beam. The corresponding debunching wavelen~lth 20 is 150 kilometers.
It is desired to maintain the electron bunches for more efficient RF energy extraction at the receiving location 16. Accordingly, an inductive cavity, i.e., a cavity resonant slightly above the frequency of the RF driving energy, i8 placed on the beam 19 every few kilometers, such as 10. These debunching cavities 78 are excited by the bunched beam entering the cavity and the fields of the cavity interact back on the electron beam to velocity-modulate the bunched beam in such a manner as to cause a rebunching of the electron. Thus, the electron beam 19 i~ received at the receiving location 16 as a well bunched current density modulated beam of high velocity, 30 as of 100 MeV. The beam i9 bunched at the frequency of the radio frequency accelerator, such as 30 megahertz.

.

1039797 ::
At the receiving location a plurality of decelerating cavities 79, tuned to the frequency of the radio frequency energy imparted to the beam, are successively coupled to the beam for extracting kinetic energy there-from and converting same to RF energy. The decelerating cavities 79 are ~-substantially identical to accelerating cavities 74 and each cavity is capable of generating a relatively high RF voltage thereacross on the order of 400 kV
per cavity.
A rectifier load 81 is connected to each of the cavity resonators 79 for rectifying the RF energy extracted from the beam. The rectified DC
10 energy is applied to an output coaxial line 82. The output DC energy on line 82 is fed to the input of an inverter 24 for producing three phase output power on lines 25-27.
Each of the resonators 7~ of the output decelerator section 83 serves to extract kinetic energy from the beam. A sufficient number of output resonators 79 is provided for extracting the kinetic energy imparted to the beam by means of the accelerator section 73. After the RF energy has been extracted from the beam, the beam may be collected on the pipe 15 or in a collector 17 coupled to the end of the pipe 15. As in the other embodiments, an output signal is derived from the inverter which is a measure of the power 20 demanded by the load. This load demand signal is fed to one input to the control circuit 28 for controlling the beam current such that the power :, .: . , delivered to the loald is equal to the power demanded by the load.
The inverter 24 may be replaced by two additional sets of recti-fiers 81 which may comprise, for example, high power triodes. Each set of triode rectifiers is connected to a respective output bus similar to bus 82.
There is one output bus for each phase of a three phase system. Each out-put bus i8 connected to a primary winding of a three phase power transfor- ;
mer. The respective sets of triode rectifiers are sequentially gated at the AC power frequency, as of 60 Hertz, with 120 phase shift between each of ;

30 the output power buses.
As an alternative, the gun 12 may be gated at the 60 Hertz power frequency and the three sets of output triode rectifiers synchronized with the 60 Hertz pulses of the beam.

An advantage to the high velocity electron beam transmission system of Fig. 16 is that the self magnetic field of the beam almost com-pletely overcomes the repulsive space charge forces generated within the beam.
As an altelnative to varying the beam current in the system of Fig. 16, for matching the power delivered to the load to the power demanded by the load, the beam current is maintained constant and the number of resonators 74 employed for accelerating the beam varied in accordance with the output power demanded by the load.
10Power is tapped off the beam intermediate the transmitting location 14 and the receiving location 16 by providing an output resonator 79 coupled in wave energy exchanging relation to the RF modulated be~ and excited ~ -by the beam. As with the other output resonators 79, the RF power ex-tracted via the cavity 79 is rectified via rectifier 81 and fed to a second load 80. The load 80 may comprise an inverter for providing three phase output power or three sets of rectifiers may be employed which are sequentially switched into a primary winding of a three phase transformer for providing inversion of the power to the load.
The intermediate output power tap comprising the resonator 79, `
20 rectifier 81, and load 80 is also utilized with any of the o~her DC trans-mission systems such as 11, 42, or Fig. 9, by pulse modulating the beam at the resonant frequency of the cavity 79 without the necessity of the accelerating and decelerating RF structures 73 and 83.
Referring now to Figs. 17-19, a number of circuits are shown for controlling the beam at the transmitting end 14 to insure that the electrons collected by the collector 17 strike the collector at nearly zero velocity so that no large amount of power is dissipated in the collector 17 (i.e. the 3ystem efficiency will be high). This zero velocity condition is realized when the cathode potential V~ = Vc = IbRL, where ~c is the collector 30 potential, Ib is the electron beam current, and RL is the load resistance presented to the collector 17.

'~
, ' ' ~; - 27 -: ' ... ... . .. . . . .

~039~797 There are two ways of accomplishing this end. First, both Vk and Ib are adjusted simultaneously so that Vk = Vc. Secondly the beam current ..................................................................................... ..... ... . .
Ib is adjusted to be equal to Vk/RL by sensing the collector voltage Vc and setting the current Ib so that Vc equals Vk.
All of the above methods rely upon a comparison circuit for com-paring Vc and Vk to derive the error control signal. The comparison circuit comprises an analog summing amplifier or a combination of analog-to-digital converters and digital summing logic of the type shown in Fig. 19.
More particularly, with regard to Fig. 19, the collector voltage Vc is fed to a first analog-to-digital converter 91 to derive a first digital output proportional to Vc. The cathode potential Vk is applied to a second analog-to-digital converter 92 to derive a second digital output proportional to Vk.
The two digital output are applied to a logic subtractor 93 for subtraction therein to derive the error signal in the form of a digital output which is thence fed to a digital-to-analog converter 94 to derive an ahalog control signal (error signal). ; - ;
The error signal, either analog or digital, which is proportional to the difference between the cathode potential Vk and collector potential Vc ~
control~ the ~ystem parameter selected for control. ~ `
Referring now to Fig. 17, l:here is shown a control circuit for matching the cathode potential Vk to the collector potential Vc. In the circuit of Fig, 17 the cathode potential Vk is varied to be equal to the collector potential Vc while allowing the beam current to vary with variations in the cathode potential. The beam current Ib will vary as a function of the cathode potential Vk according to the relation: Ib = KVk 3/2 where K is the beam perveance. ;
In the variable voltage cathode power supply 38, the difference ;
signal coming from the comparison circuitry 28 is used to vary the mechan-ical position of a variable mutual inductance transformer, such as an Inductrol~), therein for varying the output potential Vk. As an alternative, the error signal derived from the output of the comparison circuit 28 is utilized as the input signal to a phase control regulator incorporated in the variable voltage power supply 38 for varying Vk.

10397g7 Referring now to Fig. 18, there is shown the second method for matching the cathode potential Vk to the collector potential Vc. The difference signal from the output of the comparison circuit 28 is amplified a and applied to the control electrode 29 in the proper phase to reduce the difference signal to zero. In this case, the beam perveance K will vary up to some value which is dependent upon the system voltage (a constant)., and the maximum system current. The beam focus system, such as the quadru-pole, is designed to handle such a range of perveance.
In a further variation of the control system of Fig. 18 the peak 10 current of the beam Ib is maintained constant while the average current is varied in accordance with the error signal derived from the comparison circuit 28. The average current is varied by creating (in a pulse modu-lator 96) a repetitive rectangular pulse signal applied to the control grid Z9.
The duty factor of the repetitive pulse is varied by the output of the comparison circuit 28 in such a manner that the difference between the collector potential Vc and the cathode voltage Vk tends toward zero. When this control variation is used, there must be enough capacitance in the collector circuit 17 and ~e repetition frequency of the current pulse is high enough so that the collector voltage Vc does not follow the rapid variations -20 of the beam current Ib. The pulsed version of the control system of Fig. 18 impose~ the most ea~ily met requirements on the beam focus sy~tem, ~lso, the method of Fig. 18 (whether or not pulsed) is the mo~t suitable when it is desired to deliver a varying amount of power to the receiving end 16 at a constant collector voltage such as would exist in the typical power system.

. ~ ~. .'' '~ ', ' ~

~'. ~' . .

.-:
'':. -

Claims (37)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. In an electron beam power transmission system for transmitting electrical power from a transmitting location to a receiving location geo-graphically removed from the transmitting location:
elongated evacuated envelope means extending from the transmitting location to the receiving location;
transmitter means at the transmitting location for forming, accelerating and projecting a beam of electrons over an elongated beam path extending within and along said evacuated envelope from the transmitting location to the receiving location; and receiver means at the receiving location for converting the kinetic energy of the beam to electrical power for application to a power load, comprising, means for decelerating the electrons by an electric field com-ponent in the direction of their motion and means for collecting the deceler-ated electrons as conduction current.
2. The system of claim 1 further including beam focus means disposed along said beam path intermediate the transmitting and receiving locations for focusing the electron beam within said evacuated envelope, said beam focus means comprising magnet means for generating a magnetic beam focusing field within the beam path, and magnetic shield means dis-posed surrounding said magnet means and said elongated evacuated envelope.
3. The apparatus of claim 2 wherein said magnet means comprises a plural pole permanent magnet structure.
4. The apparatus of claim 2 wherein said magnet means is a plural pole magnet and comprises a plurality of circumferentially spaced electrical conductors spiraling around the outside of said envelope , and means for energizing said conductors with current to generate said plural pole beam focusing magnetic field within the beam path.
5. The apparatus of claim 3 wherein said plural pole permanent magnet structure comprises at least four circumferentially spaced permanent magnet structures disposed spiraling around the outside of said elongated evacuated envelope.
6. The apparatus of claim 1 wherein said receiver means includes an electron-collecting structure to collect the electrons of the beam, elec-trical insulator means for electrically insulating said collector structure from said elongated evacuated envelope means to allow the potential of said collector means to be depressed to within 5% of the potential of the source of electrons of the beam.
7. The apparatus of claim 1 wherein said transmitter means includes a plurality of accelerating electrodes spaced apart along the beam path, insulator means disposed between adjacent electrodes to permit different beam accelerating potentials to be applied to different ones of said accelerating electrodes, means for applying an ascending sequence of different potentials taken in the direction of beam flow to said plurality of accelerating electrodes to produce a beam accelerating electric potential gradient in and along the beam path for accelerating the electrons.
8. The apparatus of claim 1 wherein said receiver means includes, beam declerating structure comprising a plurality of decelerating electrodes spaced apart along the beam path, insulator means disposed between adjacent decelerator electrodes to permit different beam decelerating potentials to be established on different ones of said decelerating electrodes, means for applying a descending sequence of different potentials taken in the direction of beam flow through said plurality of decelerating electrodes to produce a beam decelerating electric potential gradient in and along the beam path for decelerating the electrons to a beam collecting potential.
9. The apparatus of claim 1 wherein said receiver means includes a pair of beam collector structures for each phase of output current to be supplied to the load, and receiver beam deflector means for sequentially deflecting the beam into respective ones of said beam collector structures, whereby alternating current is supplied to said load.
10. The apparatus of claim 9 wherein said transmitter means includes a pair of electron guns for each phase of alternating current to be supplied to the load at said receiver means of the power transmission system, and transmitter beam deflector means at the transmitting location for sequentially deflecting the beam current from respective ones of said electron guns into a common beam path within said elongated evacuated envelope means.
11. The apparatus of claim 10 including, means for synchronizing the beam deflecting actions of said beam deflector means at both the trans-mitting and receiving locations of the power transmission system.
12. The apparatus of claim 10 wherein the power transmission system is a three phase electrical power transmission system having six beam forming electron guns and six beam collector structures.
13. The apparatus of claim 1 wherein said transmitter means and said receiver means includes a pair of electron guns and a pair of beam collecting structures, respectively, for each phase of alternating output current to be supplied to the load at the receiving location of the power transmission system, and means for sequentially directing current from respective ones of said electron guns to respective ones of said beam collecting structures.
14. The apparatus of claim 1 including, control means responsive to the power demanded by the power load, as connected to said receiving means, for controlling the beam power transmitted from the transmitting location to the receiving location in proportion to the power load demanded at the receiving location.
15. The apparatus of claim 14 wherein said control means includes, means for deriving a beam collector signal proportional to the potential drop Vc produced by the flow of collected beam current through the power load connected to said receiver means, said transmitter means including a cathode emitter means for supplying beam current, and means for con-trolling the potential Vk of said cathode emitter means to a value within at least 10% of said collector potential Vc.
16. The apparatus of claim 14 wherein said power transmitter means includes a cathode emitter means operating at a cathode potential Vk for supplying beam current, control electrode means for controlling the value of beam current drawn from said cathode emitter means, and wherein said control means includes, means for deriving a beam collector signal proportional to the potential drop Vc produced by the flow of collected beam current through the power load connected to said receiver means, and means for controlling the potential of said control electrode means for controlling the beam current to a value such that the collector potential Vc is controlled to a value within at least 10% of the value of the cathode potential Vk.
17. The apparatus of claim 16 wherein said means for controlling the potential of said control electrode includes means for pulsing the poten-tial applied to said control electrode in such a manner that the average beam current is controlled to such a value that the collector potential Vc is controlled to a value within at least 10% of the value of the cathode potential Vk.
18. The system of claim 1 wherein said beam accelerating means includes a radio frequency wave supportive beam accelerating structure disposed in electromagnetic wave energy exchanging relation with the beam at the transmitting location and means for exciting said radio frequency accelerating structure for apply-ing the excited radio frequency electric fields of said structure to the beam path with a substantial component of said radio frequency field being directed in the direction of the beam path for bunching and accelerating the electrons of the beam; and said receiver means includes a radio frequency wave supportive receiving structure disposed at the receiving location in electromagnetic wave energy exchanging relation with said beam for excitation by the accelerated and bunched beam, and rectifier means coupled to said radio frequency wave supportive receiving structure for rectifying the radio frequency power extracted from the beam.
19. The apparatus of claim 18 wherein said radio frequency accelerator structure includes a plurality of radio frequency resonators, and means for phasing the electrical fields of said resonators for acceler-ating and bunching the electron beam.
20. The apparatus of claim 18 wherein said means for exciting said radio frequency accelerating structure includes a class C radio fre-quency amplifier means.
21. The apparatus of claim 18 including, a resonant radio frequency wave supportive electron beam rebunching structure disposed along said beam path in electromagnetic wave energy exchanging relation with the beam for rebunching the electron bunches of the beam to counteract space charge debunching effects within the beam.
22. The apparatus of claim 18 wherein said radio frequency receiving structure includes a plurality of radio frequency resonators spaced apart along the beam path in radio frequency electromagnetic wave energy exchanging relation with the beam.
23. The system of claim 1 further including means for pulsing the beam current into a train of pulses each having a pulse length of sufficiently short duration to avoid ion neutralization of the space charge of the beam and successive pulses being separated by a time sufficiently long to permit the ions to diffuse to the envelope, whereby ions formed within the beam path will drain to the walls of said elongated envelope.
24. The system of claim 1 further including ion draining electrode means disposed along said beam path in gas communication therewith for draining and collecting the ions, whereby ions formed within the beam path will be drained to said ion draining electrode means.
25. The system of claim I further including means disposed inter-mediate the transmitting location and the receiving location for extracting kinetic energy from the beam and for converting same to electrical power for application to a second power load.
26. The apparatus of claim 25 wherein said transmitter means includes, means for current density modulating the beam at a radio frequency, and wherein said means for extracting kinetic energy from the beam includes a radio frequency wave supporting structure coupled in electromagnetic wave energy exchanging relation to the beam for extracting radio frequency wave energy therefrom, and rectifier means for rectifying the radio frequency energy extracted from the beam.
27. The system of claim 1 further including means for pulsing the duty factor of the beam current for variably controlling the average beam power transmitted to the receiving location.
28. The system of claim 1 further including means coupled in radio frequency wave energy exchanging relation with the interior of said elon-gated evacuated envelope for coupling to and suppressing modes of radio frequency wave energy propagation within said envelope.
29. The system of claim 1 wherein said evacuated envelope means comprises electrically conductive pipe means and further including means for returning the beam current from the receiving location to the transmitter location via electrical conduction through the walls of said electrically conducting pipe means.
30. The apparatus of claim 29 wherein said pipe means is evacuated.
31. The system of claim 1 further including beam focus means disposed along said beam path intermediate the transmitting and receiving locations for focusing the electron beam within said evacuated envelope, said beam focus means comprising a plural pole magnet means for generating a magnetic beam focusing field within the beam path;
said transmitter means including a cathode emitter means for emitting electrons to form the beam; and said beam focus means including a main portion and a transition portion, said transition portion providing a taper in the intensity of the beam focusing magnetic field so as to gradually increase the intensity of the beam focus magnetic field from a relatively low intensity to full intensity in the beam path as a function of distance in the direction of electron flow from said cathode emitter into said main portion of said beam focus means, whereby a smooth transition to full beam focusing field intensity is obtained to mini-mize perturbations of electron beam flow.
32, The system of claim 1 further including beam focus means disposed along said beam path intermediate the transmitting and receiving locations for focusing said electron beam within said evacuated envelope, said beam focus means comprising a plural pole magnet means for generating a magnetic beam focusing field within the beam path;
said transmitter means including a cathode emitter means for emitting electrons to form the beam; and said beam focus means including a main portion disposed intermediate the transmitting and receiving locations and a transition portion at the transmitting location, said transition portion comprising a multipole astig-matic magnetic lens means for receiving the electron beam from said cathode emitter means and for focusing the received electron beam into said main portion of said beam focus means with electron trajectories matching the entrance electron trajectory requirements of said main portion of said beam focus magnet means, whereby a smooth transition of the electron flow is obtained from said cathode emitter means into the main portion of said beam focus means to minimize undesired perturbations of the electron beam flow caused by magnetic beam focus.
33. The system of claim 1 wherein said evacuated envelope com-prises an electrically conductive pipe, and further including plural pole magnet means for generating a magnetic beam focusing field within said pipe, said magnet means being disposed externally of said pipe; and magnetic shield means disposed surrounding said magnet means and said pipe for shielding the interior of said pipe from spurious external magnetic fields and for providing a magnetic return path for the magnetic flux generated by said magnet means.
34. The apparatus of claim 33 wherein said magnet means com-prises a plural pole permanent magnet structure.
35. The apparatus of claim 33 wherein said magnet means com-prises at least four circumferentially spaced electrical conductors spiraling around the outside of said pipe.
36. The apparatus of claim 33 wherein said magnet means com-prises at least four circumferentially spaced permanent magnet structures disposed spiraling around the outside of said pipe.
37. The apparatus of claim 1 further including a beam fucus means disposed along said beam path intermediate the transmitting and receiving locations for focusing the electron beam within said evacuated envelope, said beam fucus means comprising a periodic beam focus magnet structure, and wherein the period of said periodic beam focus magnet structure varies randomly along the beam path to avoid undesired radio frequency wave interaction with the beam.
CA207,199A 1973-08-20 1974-08-16 Electron beam electrical power transmission system Expired CA1039797A (en)

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CA1039797A1 (en)

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