US3225236A

US3225236A - Propulsion arrangement

Info

Publication number: US3225236A
Application number: US80143A
Authority: US
Inventors: Rudolf X Meyer
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1961-01-03
Filing date: 1961-01-03
Publication date: 1965-12-21
Anticipated expiration: 1982-12-21

Description

Dec. 21, 1965 x. MEYER 3,225,236

PROPULSION ARRANGEMENT Filed Jan. 5, 1961 I I O I 1 O 0 1 PLASMA MAGNETIC T F LD T FLOW H |2 IE I4 0' 0 ea 0 0 22 w w w w, w, w w w w F G. l

i pa FREQUENCY MULTIPLIER POLYPHASE POWER SUPPLY IN VENTOR. [3O RUDOLF X. IMEY ER 'az z sssssssssssz w F I G 4 BY @Mflf 62%) ATTORNEYS United States Patent Ohio Filed Jan. 3, 1961, Ser. No. 80,143 5 Claims. ((Il. 313-63) The present invention relates to a propulsion arrange ment and more particularly to an arrangement utilizing electromotive and magnetohydrodynamic principles for accelerating an ionized medium.

In the development of thrust devices for outer space drives it is recognized that maximum propellant utilization is obtainable by ejecting particles at extremely high velocities. To obtain maximum propellant utilization, the velocities of ejection must approach a major portion of the total velocity increment for the mission contemplated. Persons familiar With chemical reactions will immediately recognize that such velocities are not feasible to attain by known forms of combustion. On the other hand various approaches have been suggested for developing thrust by accelerating ions or charged particles and by applying high voltage electrostatic fields tothese particles to attain velocities of the order of tens of thousands of meters per second.

In accordance with the present invention, these velocities are attainable by the use of primary magnetic fields applied to an ionized medium or plasma to induce a motion in the plasma on principles utilized in induction motors. As in the case of induction motors, primary field windings create a moving magnetic field which induces a secondary current in a shunted conductor within the moving field. The secondary current develops a secondary magnetic field, tending to oppose the primary magnetic fields. As the torque developed in an induction motor is a function of the power applied to the primary windings, the thrust force of the present device applied to the plasma conductor within the primary magnetic fields is a function of the power applied to the primary windings. Similarly, the thrust is a function of the slippage between the plasma conductor and the moving primary magnetic field. In the case of an induction motor, a maximum torque is developed during maximum slippage and a maximum velocity is developed during minimum slippage.

It is, therefore, an object of the present invention to provide a propulsion arrangement for developing extremely high velocities of flow in an electrically conductive fluid medium.

It is another object of the present invention to provide a simple and reliable plasma pump arrangement.

The present invention, which may be visualized as a plasma pump, comprises a conduit containing a moving electrically conductive ionized fluid medium such that an application of magnetomot-ive thrust force to the fluid medium is feasible as a function of the relative rates of travel of the fluid medium within the conduit and a primary magnetic field developed by the energization of polyphase windings along the conduit.

In accordance with one embodiment of the present invention, polyphase windings are positioned in juxtaposed relationship along a conduit conducting a plasma. The polyphase windings are energized to develop a magnetic field which traverses the conduit longitudinally at a rate substantially above the rate of flow of the plasma entering the conduit. The magnetic fields applied to the conduit induce in the plasma a secondary current flow such that energy is absorbed by the plasma flow as a function of the relative rates of slippage between the plasma flow and the magnetic field motion. As in the case of induction motors a major portion of the energy is effective in accelerating the plasma. Thus the velocity of plasma flow is made to approach the phase velocity of the magnetic field. By increasing the phase velocity of the magnetic field along the length of the conduit, the accelerating thrust applied to the plasma may be made relatively constant whereby the velocity of the plasma may be continuously increased to a value consistent with that necessary for the particular operation contemplated.

The subject matter which is regarded as the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The present invention, however, as to its organization and operation together with further objects and advantages thereof, Will best be understood by reference to the following de scription taken in connection with the accompanying drawing in which:

FIG. 1 is a schematic illustration of basic operating elements of the present invention;

FIGS. 2a and 2b are vector diagrams illustrating the phase relationships of the several voltages and currents developed in the course of operation of the present invention;

FIG. 3 shows an embodiment of the present invention; and

FIG. 4 shows an enlarged detail of a section of the embodiment shown in FIG. 3.

Referring now to the drawing, wherein like numbers illustrate similar parts, there is shown in FIG. 1 a portion of a conduit 10 through which hot ionized gas or plasma (such as deuterium) flows from left to right as indicated by a vector 11 at the input end. Surrounding the conduit 10 is a polyphase primary winding arrangement. Any one of a number of different polyphase primary winding arrangements may be utilized; however, in order to obtain simplicity of explanation and thereby facilitate understanding of the invention, a four-phase winding arrangement is illustrated. As is well known, in a fourphase winding separate and distinct toroidal windings contain conductors which are interleaved with each other in a complex fashion known in the winding art. The four separate and distinct windings are illustrated herein as four separate turns of wire, sequentially designated in FIG. 1 as W W W and W Those turns of wire that are similarly designated are connected with each other, either in series or in parallel.

Primary currents of four different phases are respectively circulated in the four different windings, the primary currents being successively out of phase with each other by The phase relationships existing between these four primary currents are illustrated by the vector diagram of FIG. 2a wherein current flowing through winding W is designated as current vector 1 etc. Vector 1 is used as a reference and is followed by vectors 1 Iwg, and 1 each having a 90 lag with respect to one another in the order specified.

Furthermore, in order to obtain a full grasp of operating principles herein involved, the vectors of FIG. 2a are deemed to rotate in a counterclockwise direction, with reference vector I being a maximum positive value in the position shown in the vector diagram, which means that the primary current in winding W is a maximum at the instant depicted. Consequently, vector 1 represents zero current flow through winding W at the instant shown; vector 1 represents a maximum flow of primary current through winding W but in an opposite direction from the current represented by vector 1 1; and, in the position shOWn, vector 1 represents a zero current flow through winding W Relating the vector diagram of FIG. 2a to FIG. 1, current is shown to flow through windings W and W the currents therein being out of phase as indicated by the plus and dot marks placed within the circles representing winding cross-sections. Intermediate of the windings W and W there is no current flow and, therefore, the circles representing the winding W and W are blank.

Asa result of the currents indicated in the primary windings of FIG. 1, magnetic flux of the type and direction shown are established, the flux lines due to the primary currents forced to flow through the windings being indicated by arc-shaped arrows 12. It will be recognized that because the currents flowing through windings W and W are of opposite phase, the flux lines due to these currents are in the same direction in the proximity of windings W and W with the result that the radial component of the magnetic field is strengthened or enforced near these two windings. On the other hand, the radial component of the magnetic field may be said to be at a minimum or null in the proximity of windings W and W Due to the fact that the currents 1W1, 1 1 and 1 are variable, the magnetic field at any point in the conduit is also variable. It may be concluded, by reasoning used to explain polyphase electromotive equipment, that varying currents of the primary windings produce a moving primary magnetic field having a phase velocity whose wave-front moves from left to right as indicated by a vector 14.

Due to the motion of the primary magnetic field and in view of the further fact that the plasma may be considered the equivalent of a continuous stream of electrically conductive loops or secondary coils moving along the conduit 10 from left to right, a magnetic coupling is developed therebetween. In the case of the present invention, the phase velocity of the primary magnetic field as shown by the vector 14 is greater than the velocity of the plasma as shown by the vector 11. Correspondingly changing electric secondary currents are induced in the plasma in a circumferential direction. Because of the relative motion between the plasma and the primary magnetic field, alternating-current voltages are induced in the plasma of such a nature that secondary alternating electrical currents are caused to flow transversely around the plasma. Thus the primary windings and the plasma are inductively coupled to each other, with the result that the voltages induced in the plasma due to the variations of magnetic field are shifted by about 90 with respect to the currents which produce the primary magnetic field.

In view of the fact that the plasma itself is essentially of a resistive nature, the secondary currents 1 to 1 circulating around the plasma are in phase with the induced voltages V to V Accordingly, these secondary currents are also 90 out of phase with the primary currents flowing through windings W to W The vector diagram of FIG. 2b illustrates the phase relationships existing both between the voltages and currents in the plasma and between these quantities and the primary currents of FIG. 2a in the windings W W W and W To distinguish the currents in the windings from the voltages and currents induced in the plasma, the latter quantities have been designated with the subscript p, the p indicating plasma. Thus, the vectors 1 to I respectively, represent the plasma secondary currents in the vicinity of windings W to W currents I and 1 being maximum at the instant illustrated. This may be expected in view of the fact that the radial components of the primary magnetic field 12 are at a maximum at windings W and W at this instant.

The currents flowing in the plasma at the time selected in FIG. 1 are illustrated by means of broken circles, a plus in one of these circles representing in the customary fashion current flowing away from the observer while a dot centered in a circle correspondingly represents current flowing toward the observer. The secondary magnetic fields (not illustrated) associated with the plasma secondary currents develop a counter-electromotive force tending to reduce the current flow in the primary windings. The radial components of the secondary magnetic field due to the plasma current are at a maximum in the vicinity of primary windings W and W The magnetic field generated by the plasma currents varies in a sinusoidal manner longitudinally along conduit 10 and, as may be expected, this magnetic field is lagging the magnetic field of the currents through the primary windings W to W The above described four-phase arrangement was employed for convenience; that is, because of the ease and simplicity with which the underlying principles can be explained. It should be recognized, however, that the principles involved are equally applicable with respect to other types of polyphase arrangements such as threephase, six-phase, etc. Hence, any conventional polyphase induction motor will, in accordance with the principles herein delineated, have its plasma analog.

Having thus described the underlying principles of the present invention, consideration is now given to an embodiment thereof illustrated in FIG. 3. The tubular conduit 10 has a passageway 16 extending longitudinally through it. A plurality of electrical conductive windings 18 are mounted in the walls of the conduit 10. As may be seen in FIG. 3, the windings 18 are circumferentially disposed around the conduit 10 and, furthermore, they are interleaved in such a manner as to form a polyphase winding arrangement such as three-phase, six-phase, etc., winding arrangements.

The conduit 10 is tapered at its input end to form an inlet nozzle passageway 20 which constitutes the outlet of a heating and ionization chamber 22. Such a chamber as indicated schematically in FIG. 1 may be of a type that is well known and hence need not be described in detail here. By way of example, a fission reactor may be used to produce plasma. One arrangement for developing a plasma flow is described in my copending application for Letters Patent of the United States, Serial No. 855,330, entitled Gas Accelerating Method and Apparatus, filed November 25, 1959, and assigned to the assignee of the present application. This type of plasma generator develops plasma flow at a temperature of about 2000 K. (with seeding). An arc jet plasma generator will develop a plasma flow at a temperature of about 6000 K. Shock heating will develop intermittent plasma flow at a temperature of the order of 100,000 K.

As shown in FIG. 3 the plasma flows from the inlet nozzle 20 at a high velocity which is in fact a relatively low velocity compared to the magnetic field phase velocity as shown by the vector 14. Thus the resulting magnetic coupling accelerates the plasma. It is well known that the efliciency of an induction motor is very low when the slippage between the rotating primary field and the rotor is very great. Similarly the efficiency of the present invention is a monotonically increasing function of the disparity between the plasma velocity 11 and the phase velocity 14. As shown in FIG. 1, the windings developing the primary field may be spaced in a logarithmic or other differential manner whereby the phase velocity vector 14 of the primary magnetic field increases throughout the length of conduit it Thus the phase velocity vector 14 of the magnetic field in the first portion of the conduit 10 is substantially smaller than the vector 14' (FIG. 3) in the last portion of the conduit 10. Although the phase velocity of the magnetic field may be suitably controlled by the spacing of the windings as indicated in FIG. 1, it may be further controlled by the frequency of a polyphase power supply 24 which energizes the primary windings. In order to provide a higher velocity in a later portion of the magnetic field, a frequency multiplier 26 is connected between the polyphase power supply 24 and the windings 18 whereby the Windings 18 have applied thereto power at a frequency substantially greater than that applied to the windings 18. The final result is a flow of plasma from an exhaust region 28 of a velocity, as indicated by the vector 11,

that is substantially greater than that developed in the input nozzle 20.

It is also recognized that in dealing with high temperature plasma there is a problem relating to the maintaining of suitably low temperatures of the windings 18. Without thermal protection, one of the first elements destroyed by excessive heat is the insulation of the windings 18. There are two approaches to this problem which will facilitate the use of high temperature plasma. A first approach is to provide only intermittent flow of the plasma as by developing plasma pulses using high current discharges through a gaseous medium in the source 22 (FIG. 1) whereby the medium is intermittently heated to high temperatures developing plasma characteristics. In such a system the use of a polyphase primary field is not essential. Therefore, the windings, as illustrated in FIG. 1, may be used to develop individual pulses which travel along the conduit at the leading edge of the intermittent plasma pulses. Such a system may be operated either with the windings being commutated or, alternatively, with the windings being arranged to form a portion of a transmission line whereby a wave front will traverse the conduit 10 to induce acceleration of plasma pulses.

In accordance with the present invention a higher thrust arrangement utilizes a system as illustrated in FIG. 3 and in greater detail in FIG. 4 wherein a continuous flow of relatively high pressure, low velocity gas (as indicated by an arrow passes from a tank 29 (FIG. 3) to the ionization chamber 22 by a flow arrangement between the windings 18 and the passageway 16. In such a system the pressure Within the tank 29 causes the gas 30' to flow through a heat exchanger region between the passageway 16 and windings 18 to thus thermally isolate the windings from the extreme temperatures within the passageway 16.

Moreover, since the flow of the gas 30 may be arranged to be substantially laminar, the gas adjacent to a heat exchanger membrane 32 is most quickly heated. By providing a plurality of small apertures, this most heated gas is bled (arrows 34) sequentially into the passageway 16 where it will be heated further by the hot plasma 11 therein and by the thermal 1 R losses of the induction system which result in additional heat in the passageway 16. In this way, although the plasma near the center of the passageway 16 will be maintained at high tempera tures, the windings 18 are substantially protected from such temperatures.

A clearer understanding of the phenomena by which the added relatively cool gas 34 is heated becomes apparent when it is recognized that the induced currents in the plasma result in periodic constrictions 35 (FIG. 3) of the plasma whereby it travels through the passageway 16 as a succession of pulses 36 which agitate the cool gas 34 and mix it with the hot plasma 11. Moreover, in a continuous plasma flow ionization chamber 22, the velocity 11 of the plasma (and of the magnetic fields) may be substantially above the speed of sound, whereby the pulses 36 will generate shock waves which quickly heat the gas 34 added to the system so that it also becomes a conductive plasma. In connection with the high temperature problem, a unidirectional magnetic field may be generated by the linear windings 38. The most conductive (and the hottest) plasma is constricted b this unidirectional field to the center of the passageway 16 whereby the temperature of the plasma adjacent to the heat exchanger membrane 32 is minimized. Because of the high currents necessary to constrict eflectively the hot plasma, it is preferred that the windings 38 and a unidirectional power source 40 have a minimum impedance to reduce to a minimum the PR losses of the constriction arrangement. The use of the unidirectional constriction arrangement will limit the temperature such as 4000 K. from that defined by the isothermal envelope 42 to that defined by the isothermal envelope 44. Such constriction results in the isothermal envelope 42 defining a temperature of about 2000 K.

While there have been shown particular embodiments of the present invention, other modifications may occur to those skilled in the art. For instance, various selective propulsion arrangements may be used to provide steering of the exhaust stream as well as accelerating thrusts. Moreover, it may be desired to insert certain amounts of inert matter, such as waste products, in a manner similar to water injection in commercial jet engines whereby this matter will also be accelerated and will add mass to the plasma 11 flowing from the exhaust region 28. It is intended, therefore, by the appended claims to cover all such modifications as come within the true spirit and scope of the present invention.

What is claimed is:

l. A plasma pump comprising: a conduit having one end arranged to receive a plasma flowing at a relatively low initial velocity and being arranged to exhaust the plasma at its other end; a polyphase power source; a first plurality of windings along said conduit adjacent to the one end, arranged to be energized by said power source to develop a magnetic field along said conduit, which magnetic field moves parallel to the motion of said plasma and at a phase velocity greater than the initial velocity whereby currents are induced in said plasma and a magnetic coupling between said plasma and the moving magnetic field will thrust said plasma through the conduit at a second velocity greater than the initial velocity; a frequency multiplier coupled to be energized by said power source to provide a higher frequency power output; and a second plurality of windings along said conduit adjacent to the other end arranged to be energized by said higher frequency power output to develop a magnetic field along said conduit which moves parallel to the motion of said plasma and at a phase velocity greater than the second velocity to accelerate further said plasma.

2. A plasma accelerating arrangement comprising: a conduit having one end arranged to receive a very hot, electrically conductive plasma flowing at a relatively low initial velocity; an electric power source; a polyphase winding along said conduit adjacent to the one end, arranged to be energized by said power source to develop a magnetic field which moves along said conduit parallel to the motion of said plasma and at a phase velocity greater than the initial velocity whereby currents are induced in said plasma and a magnetic coupling between said plasma and the moving magnetic field will pump said plasma through the conduit to attain a velocity greater than the initial velocity; and means forming a passageway between said plasma and said windings and communicating with said plasma for thermally protecting the region of said winding from the heat of said plasma to prevent destruction of the insulation of said windings.

3. A plasma accelerating arrangement comprising: a conduit having one end arranged to receive a very hot, electrically conductive plasma flowing at a relatively low initial velocity; a polyphase electric power source; a plurality of windings along said conduit adjacent to the one end, arranged to be energized by said power source to develop a magnetic field which moves along said conduit parallel to the motion of said plasma and at a phase velocity greater than the initial velocity whereby currents are induced in said plasma and a magnetic coupling between said plasma and the moving magnetic field will pump said plasma through the conduit to attain a velocity greater than the initial velocity; and a heat exchanger membrane secured in a spaced relation from said windings to be heated by said plasma, said membrane defining a passage between said plasma and said windings communicating with said plasma for cool gas to be heated by said membrane.

4. A plasma accelerating arrangement comprising: a conduit having one end arranged to receive a very hot, electrically conductive plasma flowing at a relatively low initial velocity; It polyphase electric power source; a plurality of windings along said conduit adjacent to the one end, arranged to be energized by said power source to develop a magnetic field which moves along said conduit parallel to the motion of said plasma and at a phase velocity greater than the initial velocity whereby currents are induced in said plasma and a magnetic coupling between said plasma and the moving magnetic field will pump said plasma through the conduit to attain a velocity greater than the initial velocity; and a heat exchanger membrane secured in a spaced relation from said windings to be heated by said plasma, said membrane defining a passage for laminar gas flow, and defining a plurality of apertures through which the hottest of the gas flow therein may bleed into said conduit.

5. A plasma accelerating arrangement for developing very high velocity of high temperature plasma, comprising: a hollow cylindrical conduit having one end arranged to receive a relatively low velocity plasma and its other end arranged to exhaust high velocity plasma; an input nozzle at the one end; a plurality of toroidal turns of wire in the form of polyphase windings arranged along said conduit; means for coupling to said windings power of differing frequency for developing in said conduit a magnetic field which moves parallel to the motion of said plasma at a phase velocity greater than the relatively low velocity whereby secondary currents are induced in said plasma to provide a magnetic coupling References Cited by the Examiner UNITED STATES PATENTS 2,819,423 1/1958 Clark 315111 X 2,826,708 3/1958 Foster 6035.5 2,920,236 1/1960 Chambers 313-157 X 2,945,119 7/1960 Blackman 315111 X 2,952,970 9/1960 Blackman 6035.5 2,956,195 10/1960 Luce 313-161 X 2,992,345 7/1961 Hansen 3l3161 X 3,016,693 1/1962 Jack et al. 6035.5

OTHER REFERENCES Engineering publication, Oct. 28, 1958, pages 474, 375.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, ABRAM BLUM, ARTHUR GAUSS, Examiners.

Claims

1. A PLASMA PUMP COMPRISING: A CONDUIT HAVING ONE END ARRANGED TO RECEIVE A PLASMA FLOWING AT A RELATIVELY LOW INITIAL VELOCITY AND BEING ARRANGED TO EXHAUST THE PLASMA AT ITS OTHER END; A POLYPHASE POWER SOURCE; A FIRST PLURALITY OF WINDINGS ALONG SAID CONDUIT ADJACENT TO THE ONE END, ARRANGED TO BE ENERGIZED BY SAID POWER SOURCE TO DEVELOP A MAGNETIC FIELD ALONG SAID CONDUIT, WHICH MAGNETIC FIELD MOVES PARALLEL TO THE MOTION OF SAID PLASMA AND AT A PHASE VELOCITY GREATER THAN THE INITIAL VELOCITY WHEREBY CURRENTS ARE INDUCED IN SAID PLASMA AND A MAGNETIC COUPLING BETWEEN SAID PLASMA AND THE MOVING MAGNETIC FIELD WILL THRUST SAID PLASMA THROUGH THE CONDUIT AT A SECOND VELOCITY GREATER THAN THE INITIAL VELOCITY; A FREQUENCY MULTIPLIER COUPLED TO BE ENERGIZED BY SAID POWER SOURCE TO PROVIDE A HIGHER FREQUENCY POWER OUTPUT; AND A SECOND PLURALITY OF WINDINGS ALONG SAID CONDUIT ADJACENT TO THE OTHER END ARRANGED TO BE ENERGIZED BY SAID HIGHER FREQUENCY POWER OUTPUT TO DEVELOP A MAGNETIC FIELD ALONG SAID CONDUIT WHICH MOVES PARALLEL TO THE MOTION OF SAID PLASMA AND AT A PHASE VELOCITY GREATER THAN THE SECOND VELOCITY TO ACCELERATE FURTHER SAID PLASMA.