US3886398A

US3886398A - Electron beam electrical power transmission system

Info

Publication number: US3886398A
Application number: US389913A
Authority: US
Inventors: Joseph Feinstein
Original assignee: Varian Associates Inc
Current assignee: Varian Medical Systems Inc
Priority date: 1973-08-20
Filing date: 1973-08-20
Publication date: 1975-05-27
Anticipated expiration: 1992-05-27

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

United States Patent [191 A Feinstein 1 1 ELECTRON BEAM ELECTRICAL POWER TRANSMISSION SYSTEM [75] Inventor: Joseph Feinstein, Menlo Park, Calif.

[73] Assignee: Varian Associates, Palo Alto, Calif.

[22] Filed: Aug. 20, 1973 [21] Appl. No.: 389,913

[52] US. Cl. 315/; 315/35; 321/22;

321/32; 321/37; 328/227; 328/233 [51] Int. Cl. H01] /02 [58] Field of Search 315/35, 4, 5; 328/233,

[56] References Cited UNITED STATES PATENTS 2,953,750 9/1960 Christofilos 328/233 3,189,750 6/1965 Dain et al. 321/65 X 3,219,904 11/1965 Osepchuk 321/8 R 3,462,636 8/1969 Seunik et 321/32 X 3,479,577 11/1969 Ruden 315/ X 3,489,943 l/l970 Denholm 328/233 X 3,644,778 2/1972 Mihran et a1. 315/35 3,700,945 10/1972 Friedman et al 315/35 Primary ExaminerSaxfield Chatmon,'.1r. Attorney, Agent, or Firm-Stanley Z. Cole; D. R. Pressman; H. E. Aine [57] ABSTRACT Electrical power is transmitted from a transmitting 10- 31 AC. m

CONlRtL CIRCUIT [4 1 May 27, 1975 cation to a remote receiving location by means of an electron beam injected into an evacuated magnetically shielded pipe extending between the transmitting loca tion 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 IOK'aLlOI'l and converted into potential electrical energy for application to the load. In one embodiment, the kinetic energy is ex tracted 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.

7 Claims, 21 Drawing Figures llNERTER PATENTEDWEY ms 3'8 FIG? CONTROL DEFLECTION FIG. 5

PATHHEB 2m 2 7 ms W Li I 8 a: FIG. I4 47 48 3 4 48 I2 I5 I? VOLTAGE WAVEFORM (SINE WAVE) FIG. l5

J L 1 CURRENT WAVEFORM SHEET NEWER MAY 27 1915 Q1) 1 F 2 2 f 8 1+ 5% 658 .\\J|/ w F .1? g E 10 11 g 1 .1 v 1 v 2% F E 9 m t J p N 25%;; AM k I I v 02 gswm PATENTEB MAY 2 7 ms SHEET 6 J COMPARATOR CIRCUIT Vc RL FIG. l9

Su %%'T0R DTOA 3%? @0593 ELECTRON BEAM ELECTRICAL POWER TRANSMISSION SYSTEM BACKGROUND OF THE INVENTION The present invention relates in general to electrical power transmission 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 by means of 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 is disclosed in U.S. Pat. No. 2,953,750 issued Sept. 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 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 Hertz or, as an alternative, the pulse repetition rate could be in the radio frequency range by utilizing 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 decelerated the beam pulses in accordance with the amount of power demanded by the load. The decelerated (unused) pulses of beam current were returned to the sending end by means of return magnetic cables or pipes 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 problem with the use of magnetic induction accelerators operating even at conventional power frequencies is that a vast amount of iron must be used causing attendant iron losses due to hysteresis effects.

SUMMARY 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, an alternating potential at the power frequency to be transmitted to the load, is applied to an electron gun at the transmit ting end to produce an electron beam from the gun during only every other half cycle of the applied alternating beam potential, whereby the AC power transmission system employs the self-rectifying action of the electron gun for transmitting the beam power to the load.

In another feature of the present invention, a polyphase transmission system is obtained wherein a plurality of electron guns are each energized with alternating potential at the power frequency to produce respective beams from said guns during every other half-cycle of the alternating potential applied to each gun, there being at least one gun for each phase of the polyphase power transmission system.

In another feature of the present invention, the transmitter location includes a plurality of electron guns for supplying a plurality of electron beams extending through individual evacuated envelopes to the power receiving location, the receiving location has a plurality of electron collectors for extracting energy from and collecting the respective beams, there being at least one electron collector for each one of the electron guns.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic longitudinal sectional foreshortened view, partly in block diagram form, of an electron beam power transmission system incorporating features of the present invention.

FIG. 1A 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.

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 por tion of the structure of FIG. I delineated by line 33,

FIG. 4 is a schematic longitudinal sectional view of a portion of FIG. I 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 transformers of the circuit of FIG. 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 77,

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 present invention,

FIG. 10 are waveforms of beam voltage, beam current, and grid voltage for an electron beam power transmission system employing an interrupted beam,

FIG. 11 is a schematic line diagram of an electron beam power transmission system employing alternative features of the present 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 de lineated by line l3-13,

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,

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 embodiment of FIGS. 17 and 18.

DESCRIPTION OF THE PREFERRED 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 l2 and a DC beam accelerator section 13 at the power transmitting end 14 of an elongated evacuated envelope 15 which extends for a substantial distance, e.g. 0.l to l,000 miles, to a remote power receiving location 16 at the receiving end of the transmission system 1. 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.

Briefly, electron gun 12 serves to form, accelerate and project a 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. In this manner, substantial kinetic energy is imparted to the electron beam.

Although a separate accelerator section 13 is 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. The beam is magnetically confined in envetope 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 and 1A) 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 ewe lope 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 US, Pat. No. 2,953,750. The envelope 15 is evacuated by means of a pluraiity of glow discharge getter-ion vacuum pumps 23 or any other suitable vacuum pump disposed at suitable inter vals along the pipe 15 in gas communication therewith for evacuating same to a relatively low pressure as of 10 torr. Thus a beam can be transmitted for hundreds of miles through tubular envelope 15 without substantial loss of energy.

As an alternative to the use of the quadrupole lens 21, the quadrupole beam focus structure 22 is extended into a transition region between the cathode 31 of the gun l2 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 energy. 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.

The collected beam current is caused to flow through an inverter load 24 to the vacuum 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. In a typical example, the beam 19 has a current of l,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 V of the beam collector 17 and compares it with the potential V of the source of electrons to derive an error signai for controlling the beam current via a control electrode 29 in the electron gun 12 or adjustment of V 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, such as 1,000 amps. Cathode emitter 31 is heated to thermionic emission temperature by means of a filamentary heater 32. Operating power is supplied to the filamentary heater 32 from a power supply 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, is disposed immediately adjacent the surface of the cathode emitter 31 and the control grid has apertures aligned with the apertures in the shadow grid. As an alternative to a control grid, a modulating anode may be employed 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 emitters for individual electron beamlets passing through the aligned openings 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 US. Pat. No. 3,558,967, issued .Ian. 26, 197], and assigned to same assignee as the present invention.

In a typical example, thermionic cathode emitter 31 comprises an impregnated tungsten matrix cathode approximately lS cm. in diameter and having an area of approximately 350 cm. 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 years 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 article entitled Electrostatic Generators for the Acceleration of Charged Particles" appearing in Reports on Progress in Physics, Vol. llzl-l8 (I948). Briefly, this type of accelerator includes a sequence of generally planar centrally apertured plate shaped electrodes 35 wherein the accelerating potential, as of 0.l to 5 million volts, is evenly dis tributed among a number of the accelerating electrodes 35. A potential divider 36 employs a string of resistors to divide the beam potential V for application of respectively increasing potentials to the respective ones of the accelerating electrodes 35. The potential difference between successive electrodes 35 in the accelerator section 13 is preferably less than 200 kilovolts to prevent arcing between the adjacent electrodes 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 stream. In a typical example, the beam would be converted from a diameter of 15 cm. at cathode emitter 31 to approximately a diameter of 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 negative cathode voltage V as of 0.1 to 5 million volts.

FIG. 2 shows, in section, the evacuated envelope and beam 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 conductor 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 the 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 electrically insulated from earth such as by the ferrite permanent magnets 22. In a typical example, aluminum pipe 15 has a diameter of approximately 10 cm. and a wall thickness of approximately 3 mm.

The beam focus permanent magnets 22 are disposed around pipe 15 at 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 poles alternating in polarity in the circumferential direction around the pipe 15. Although the preferred embodiment utilizes a quadrupole magnetic structure, other multiple pole structures may also be used, such as 6, 8, 10 or 12 poles etc. Also other types of magnetic focusing 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 electromagnetic 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 structure comprises four conductors 40 spiraling around the pipe 15 in 90 cir cumferentially spaced relation (see FIG. 2A), and energized with direct current of opposite direction in adjacent conductors 40.

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 vector 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 forces 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 l 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 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 neutralization is required. The simplest way to obtain ion neutralization is to turn off the beam periodically for a few microseconds to allow the ions to move to the wall of the pipe 15, where their charge will be lost. The time required for ion neutralization of the beam at a pressure of torr at an electron energy of l megavolt is about 5 milliseconds, Thus, the beam is turned off by means of grid 29 every few hundred microseconds, 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 suit able spacings along and within the pipe for generation of periodic electric fields (potential wells) for drawing the ions to the electrons. 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 l00 to l ,000 V, for collecting and draining positive ions from within the pipe 15. Various suitable ion draining electrodes and schemes are disclosed in U.S. Pat. No. 2,963,605 issued Dec. 6, l970.

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 is commercially available at 2,000 gauss and 2,000 oersteds in which the ferrite particles are bonded in a flexible plastic so that half of the energy product of the oriented ferrite is sacrificed for the convenience of flexible plastic bonding. Such a material has sufficient magntic energy for this application. This material is also relatively inexpensive in large quantity. Any other permanent magnetic material might be substituted.

For a permanent magnet focus system capable of focusing, for example, a l megavolt, L000 ampere beam, the energy stored in the focusing field is 0.69 joule per meter of length; therefore, 16,000 cubic 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 so as not to contaminate the vacuum. A tubular magnetic shield 4] 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 magnetic field required inside of the pipe 15 for focusing the beam is in the range of 100 to 200 gauss.

The vacuum envelope 15 is evacuated by a plurality of glow discharge getter ion vacuum pumps, such as Vaclon pumps commercially available from Varian Associates of Palo Alto, Cal. These pumps have no moving parts, produce extremely clean vacuums free from any oil contamination 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 1iter 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 values of beam voltage and current and as a function of the diameter and length of the pipe 15, microwave electromagnetic interaction may be obtained between space charge waves of the beam 19 and microwave energy propagating within the pipe !5. 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 lossy 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 evacuated chamber 6 containing an array of resistive card wave energy absorbers 7 is coupled to the microwave fields of the pipe 15 via a suitable coupling slot or hole 8. As an alternative, the inside wall of the pipe 15 may 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 is varied by, for example, 1- 20 percent in a random way to avoid cu mulative fast wave beam-field interactions and their resulting oscillations.

At the receiving location 16 the beam decelerating section 18, similar to the beam accelerator section 13 except turned end-for-end, serves to decelerate the beam to a beam voltage as close as possible to the voltage of the cathode emitter 31, namely, V without refiecting beam current to the decelerator section l8.

The decelerated beam is received within the depressed beam collector structure 17; the collector operates at a potential V approximately equal to the decelerated beam or source potential V In a preferred embodiment, the depressed collector structure 17 is of the type disclosed and claimed in U.S. Pat. No. 3,453,482 issued July 1, 1969 and preferably includes the improvement of the center spike as disclosed and claimed in copending U.S. patent application Ser. No. 283,433 filed Aug. 24, 1972, both assigned to the same assignee as the present invention. The depressed collectors of this type are very efficient and operate with beam collecting efficiencies of 98 percent, i.e., only 2 percent of the transmitted power is lost in the collector 17. However, in a one gigawatt transmission system with 98 percent 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. Pat. Nos. 3,374,523 issued Mar. 26, l968 and 3,4l4,757 issued Dec. 3, 1968 and assigned to the same assignee as the present invention. The collector should be sealed in size such that the power dissipation on the interior surfaces thereof results in a power density of below l 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 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 c. Energy is transmitted instead 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 generation and elimination of unsightly towers or excavations in either underground or above ground installations justify its use. Pipe 15 may be installed 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.

FIGS. -8 show a polyphase electric power transmission system 42 similar to that previously described with regard to FIGS. l-2 with the exception that the rectification and inversion functions have been combined with the transmission system. More particularly, six separate electron guns l2 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 magnetically shielded and magnetic focused pipe 15 leading to the receiving location I6. A magnetic deflection yoke 43 is provided at the confluence of the respective beam input pipes IS, at the transmitting location I4, for sequentially and selectively deflecting the electron beams from re spective ones of the electron guns 12 into common pipe 15.

Similarly, at the receiving location 16 the main transmission pipe 15 splits into six separate pipes I5 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-totarget deflection systems of high energy particle accel erating machines such as at the Stanford Linear Accelerator Center at Stanford, Cal.

Input power to be transmitted to the receiving location I6 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 configuration as shown in FIG. 6 and the secondary windings 47 of the input transformer 46, as shown in FIG. 7, are each center-tapped at ground or V, 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 pair of guns 12 for a respective phase of the three phase transmission 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 coupled to the other gun. Due to the self 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 360/2p where p is the number of phases for the polyphase transmission system 42. In the case of a three phase system utilizing six electron guns, 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 synchronized 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 synchronize 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 respective pair of collectors connected to opposite ends of one of three center tapped primary windings 52 of an output transformer 53. The secondary windings 54 of the output transformer 53 are connected in the delta configuration as shown in FIG. 6. An output voltage Vc is sensed across each of the respective 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 more 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 each of the respective collectors, the current pulses delivered to the primary windings 52 of the output transformer 53 will be rich in harmonics of the power frequency.

However, the connection of the collectors l7 ofeach 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 (Le. 60 Hz). In addition, the balanced connection of the collectors I7 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 52. The third harmonic and multiples thereof are effectively cancelled by using the delta connected secondary windings. The fifth, seventh, eleventh, thirteenth, etc. odd harmonics are bypassed by means of multiplicity of series resonant filters, such as filter 56, tuned for each respective odd harmonic and connected in shunt with the respective primary output winding 52.

The delta winding connection for cancelling of the third harmonic and multiples thereof is only operative in a three phase system or multiples of a three phase system. Accordingly, in a single phase or two phase system series resonant bypass filters 56 are employed for each third harmonic or odd multiples thereof, such as 3rd, 9m, l5th, etc.

Typically, the lowest harmonic will have the largest amplitude. Thus, a fifth harmonic filter 56 may suffice dependent upon the shape of the beam current pulse. Also the beam current pulse is preferably shaped by a waveform shaping circuit which shapes the control electrode potential to reduce the fifth, seventh, eleventh, thirteenth, etc. harmonics of beam current. Such a wave shaping circuit is contained 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, there is a certain value of beam conduction angle which will reduce any given harmonic of the pulse repetition frequency of beam current to zero. Thus, the wave shaping circuit controls the beam conduction angle to minimize the certain harmonic. Each of the primary windings 52 has a bypass capacitor 57 connected in parallel with the inductance of each of the primary windings 52 for bypassing harmonics 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. 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 180 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 [80 beam conduction phase angle during each conductive half cycle of the applied alternating beam potential. The reason for this is that at relatively low values of beam voltage v,,, the electrons have relatively low velocities and thus corresponding relatively long transit times through the pipe 15. In such a case, some overtaking of the slow electrons may be obtained by subsequent fast electrons. This has a deleterious effect upon the beam collector efficiency since, for high collector efficiency, all the electrons at a given instant in time should have the same velocity. Also, such overtaking will cause distortion of the current waveform, usually increasing the unwanted harmonic content thereof. Also, the beam focus system, depending upon the particular magnetic focusing scheme 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 value of beam current greater than l/6 of the peak or maximum beam cur rent, IMAXIG.

Referring now to FIG. 10, there is shown the waveforms for beam current l beam voltage V,, and control electrode voltage V and V The beam conduction angle is readily controlled by applying a fixed DC nega tive bias voltage V, to each of the respective control electrodes 29 such that the beam conduction angle is limited to that portion of the cycle corresponding to a respective grid voltage exceeding the cathode voltage V,,. 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 V Returning again to FIG. 9, it is desirable to control the power factor of the load as reflected into each of the primary windings 52 of the output transformer 53 such that the collected beam current I is in phase with the respective collector potential V... Accordingly, a continuously variable reactance, such as that provided by a synchronous condenser 58, is preferably connected across each of the respective output delta connected secondary windings S4. A voltage is derived which is proportional to the collected beam current I,.. 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 V. as derived from sensor 55 to derive an error output which is fed to the field control of the synchronous condenser 58 for causing the condenser 58 to take the proper value of reactance to bring the beam collector current l into phase with the collector voltage V 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 magneti cally shielded pipe 15 is employed for each phase of the AC power transmission system. More particularly, con vergent and divergent pipes 15, as previously described with regard to FIG. 5, are employed at the 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 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 guns. The advantage of the system 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 alterna tive embodiment to that portion of the structure of FIG. ll delineated by line 13l3. More particularly, the input deflection magnet 43 is replaced by strong" magnetically focused and convergent input pipes 15''. 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 regard 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 pipe 15 per phase of the three phase system 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. I4 and 15, there is shown an alternative multiple pipe polyphase A.C. transmission system 62. Transmission system 62 is similar to that of FIG. 5 with the exception that a pair of pipes 15 is 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 of phase angle where p is the number of phases. In the case of a three phase system, the conduction of current is preferably limited to a phase angle such that the current conducted has a value greater than 1/6 lmax, where [max is the peak beam current for each phase. This means that current is conducted from each gun for approximately l20-l40 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 IS. A second advantage is the elimination of the

magnetic 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 prevent 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 system 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 of FIG. 11 for sequentially deflecting beams from respective pairs of guns 12 into and out of the respective common pipe 15. In this latter system, 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 to relatively high energies, for example, 100 MeV.

The radio frequency accelerator 73 comprises a plurality of individual cavity resonators 74, as of 250 such cavities, sequentially 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 resonators 74 are of the folded half wavelength type as used in the accelerator at the National Accelerator Laboratory of Batavia, Illinois. The 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 providing high efficiency. i.e., greater than 90 percent in class C operation with small angle 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 plasmafrequency is proportional to the driving frequency. The plasma frequency for a 30 megahertz driving frequency is about 2,000 hertz for a l ampere, 100 megavolt beam. The corresponding debunching wavelength is ISO kilometers.

lt 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, is placed on the beam 19 every few kilometers, such as 10. These rebunching 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 is received at the receiving location 16 as a well bunched current density modulated beam of high velocity, as of MeV. The beam is bunched at the frequency of the radio frequency accelerator, such as 30 meghertz.

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 therefrom 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 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 79 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 demanded by the load. This load demand signal is fed to one input ot the control circuit 28 for controlling the beam current such that the power delivered to the load is equal to the power demanded by the load.

The inverter 24 may be replaced by two additional sets of rectifiers 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 output bus is connected to a primary winding of a three phase power transformer. The respective sets of triode rectifiers are sequentially gated at the AC power frequency, as of 60 Hertz, with phase shift between each of 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 completely overcomes the repulsive space charge forces generated within the beam.

As an alternative 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.

Power is tapped off the beam intermediate the transmitting location 14 and the receiving location I6 by providing an output resonator 79 coupled in wave energy exchanging relation to the RF modulated beam and excited by the beam. As with the other output resonators 79, the RF power extracted 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, rectifier 81, and load 80 is also utilized with any of the other DC transmission 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. l7l9, a number of circuits are shown for controlling the beam at the transmitting end 14 to insure that the electrons collected by the collector l7 strike the collector at nearly zero velocity so that no large amount of power is dissipated in the collector l7 (i.e. the system efficiency will be high). This zero velocity condition is realized when the cathode potential V =l R where V is the collector potential, I is the electron beam current, and R, is the load resistance presented to the collector 17.

There are two ways of accomplishing this end. First, both V,, and 1,, are adjusted simultaneously so that V Secondly the beam current l,, is adjusted to be equal to V /R by sensing the collector voltage V and setting the current l so that V equals V All of the above methods rely upon a comparison circuit for comparing V and V to derive the error con trol signal. The comparison circuit comprises an analog summing amplifier or a combination of analog-todigital converters and digital summing logic of the type shown in FIG. 19. More particularly, with regard to FIG. 19, the collector voltage V is fed to a first analogto-digital converter 91 to derive a first digital output proportional to V The cathode potential V;, is applied to a second analog-todigital converter 92 to derive a second digital output proportional to V 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-toanalog converter 94 to derive an analog control signal (error signal).

The error signal, either analog or digital, which is proportional to the difference between the cathode potential V and collector potential V, controls the system parameter selected for control.

Referring now to FIG. 17, there is shown a control circuit for matching the cathode potential V to the collector potential V,.. In the circuit of FIG. 17 the cathode potential V,, is varied to be equal to the collector potential V while allowing the beam current to vary with variations in the cathode potential. The beam current I will vary as a function of the cathode potential V according to the relation: I =KV 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 mechanical position ofa variable mutual inductance transformer, such as an lnductrol,

therein for varying the output potential V 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 V Referring now to FIG. 18, there is shown the second method for matching the cathode potential V to the collector potential V The difference signal from the output of the comparison circuit 28 is amplified 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 quadrupole, is designed to handle such a range of perveance.

In a further variation of the control system of FIG. 18 the peak current of the beam I 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 modulator 96) a repetitive rectangular pulse signal applied to the control grid 29. 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 V and the cathode voltage V tends toward zero. When this control variation is used, there must be enough capacitance in the collector circuit l7 and the repetition frequency of the current pulse is high enough so that the collector voltage V.- does not follow the rapid variations of the beam current I,,. The pulsed version of the control system of FIG. 18 imposes the most easily met requirements on the beam focus system. Also, the method of FIG. 18 (whether or not pulsed) is the most 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.

What is claimed is:

1. In an electron beam power transmission system for transmitting electrical power from a transmitting locatron to a remote receiving location:

elongated evacuated envelope means extending from the transmitting location to the receiving location, said receiving location being geographically re moved from the transmitting location; transmitter means at said transmitting location for accelerating and projecting a beam of electrons through said evacuated envelope means from said transmitting location to said receiving location;

receiver means at said receiving location for converting kinetic energy of the beam to electrical power for application to a power load, said receiver means comprising collector means for collecting the electrons as conduction current;

electrical conductor means interconnecting said re ceiver means and said transmitter means for returning said conduction current to said transmitter means;

said transmitter means including an electron gun having a cathode emitter for emitting electrons and an electron permeable anode electrode for drawing a stream of emitted electrons from said cathode emitter to form an electron beam emergent from said anode electrode;

means for supplying to said cathode emitter a potential alternating with respect to the potential of said conductor means for causing said gun to produce an electron beam during only every other halfcycle of said alternating potential;

said receiver means including means for developing a potential on said collector means alternating with respect to the potential of said conductor means for converting kinetic energy of the beam to alternating electrical power.

2. The apparatus of claim 1 wherein the power transmission system is a polyphase system and wherein said transmitting means includes a plurality of electron guns, these being at least one gun for each phase of the polyphase power transmission system, and wherein said elongated evacuated envelope means includes a plurality of said elongated evacuated envelopes, there being at least one envelope for each one of said electron guns.

3. The apparatus of claim 2 wherein said receiver means includes a plurality of electron collectors, there being at least one electron collector for each one of said electron guns.

4. The apparatus of claim 3 wherein said receiver means includes first and second electron collectors for collecting the electrons, electrical insulator means for insulating said first and second collectors from said evacuated envelope means to permit independent potentials to be established on said collectors relative to said envelope, means for causing electrons to be collected in a sequence in said first and second electron collectors, inductive winding means connected to said first and second collectors for flow of collected beam current therethrough for presenting an alternating power load to said respective collectors.

5. The apparatus of claim 4 wherein said receiver means includes an output power transformer means. and said inductive winding means comprises a primary winding means of said transformer.

6. The apparatus of claim 4 wherein there are at least three electron guns and three electron collectors for transmitting and for supplying three phase output power to the load at the receiving end of the transmission system.

7. The apparatus of claim 6 including a three phase input winding means for applying three phase alternating potentials and beam current to said three electron guns.

Claims

1. In an electron beam power transmission system for transmitting electrical power from a transmitting location to a remote receiving location: elongated evacuated envelope means extending from the transmitting location to the receiving location, said receiving location being geographically removed from the transmitting location; transmitter means at said transmitting location for accelerating and projecting a beam of electrons through said evacuated envelope means from said transmitting location to said receiving location; receiver means at said receiving location for converting kinetic energy of the beam to electrical power for application to a power load, said receiver means comprising collector means for collecting the electrons as conduction current; electrical conductor means interconnecting said receiver means and said transmitter means for returning said conduction current to said transmitter means; said transmitter means including an electron gun having a cathode emitter for emitting electrons and an electron permeable anode electrode for drawing a stream of emitted electrons from said cathode emitter to form an electron beam emergent from said anode electrode; means for supplying to said cathode emitter a potential alternating with respect to the potential of said conductor means for causing said gun to produce an electron beam during only every other half-cycle of said alternating potential; said receiver means including means for developing a potential on said collector means alternating with respect to the potential of said conductor means for converting kinetic energy of the beam to alternating electrical power.

5. The apparatus of claim 4 wherein said receiver means includes an output power transformer means, and said inductive winding means comprises a primary winding means of said transformer.