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Publication numberUS3150483 A
Publication typeGrant
Publication dateSep 29, 1964
Filing dateMay 10, 1962
Priority dateMay 10, 1962
Publication numberUS 3150483 A, US 3150483A, US-A-3150483, US3150483 A, US3150483A
InventorsMayfield Earle B, Vernal Josephson
Original AssigneeAerospace Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Plasma generator and accelerator
US 3150483 A
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Description  (OCR text may contain errors)

Zwl.

Sept. 29, 1964 E. B. MAYFIELD ETAL 3,150,433

Pusmcaum'ron AND Accswmron nud lay 1o. 1962 F l G. I

h- POWER l SUPPLY HEAVY FUEL Emi B. MAYFIELD VERNAL JOSEPHSON INVENTORS.

ATTORNEY.

United States Patent O 3,150,483 PLASMA GENERATOR AND ACCELERATOR Earle B. Mayfield, Torrance, and Vernal Josephson, Palos The present invention relates to the magnetohydrodynamic art and more particularly to a high-specific impulse engine suitable for space operation.

Magnetohydrodynamic prior art includes several proposed ionic thrust devices arranged to accelerate ions to high velocities suitable for space vehicle propulsion. Although, with presently available power supplies, the thrust of such engines is relatively small, their efficiency is extremely high in proportion to the fuel mass consumed and the thrust is suicient to accelerate vehicles from orbital to deep space velocities. Specific impulses of the order of 10,000 seconds are contemplated. In one type of prior art arrangement, specific-impulse engines have admitted thereto ionizable or ionized material through numerous apertures around the periphery of the engine chamber. This approach results in several problems including non-uniformity of the ejected mass whereby the thrust obtainable is relatively undeterminable, and the overall system has less than maximum thrust and efficiency.

It is, therefore, an object of our invention to provide a new and improved specific-impulse space engine.

According to one embodiment of the present invention a light-gas propulsion fuel is admitted into a thrust chamber continuously from a central porous emitter.` The emitter is arranged to allow the gas to diffuse through a central electrode into the engine chamber, as soon as the density within the engine chamber reaches approximately 101 particles per cubic centimeter the system is ionized and pulsed (or swept) by a magnetic field in the manner of operation of wave propagation through a coaxial cable. The speed of the sweeping magnetic field is of the order of 105 meters per second, and, when using light-gases such as hydrogen, or deuterium, substantially all of the ions ow from the engine at this velocity.

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

FIG. 1 is `a partially schematic side sectional view of an engine component illustrating one embodiment of the present invention;

FIG. 2 is a modiiication of the embodiment shown in FIG. 1; and

FIG. 3 is a schematic view of an engine utilizing several of the engine components of FIG. 1.

Referring now to the drawing wherein like numbers refer to similar parts, in FIG. 1 a cylindrical engine chamber or driving section is substantially enclosed around its lateral surface and one end by a housing 10.

A power supply 11 energizes a field or pulse coil 12 to generate a sweeping magnetic field 13 that passes from the closed end to the open end of the housing 10 to ionize and sweep any gas particles 14 through the engine exhaust port 16. The selection of the most appropriate mode of operation of the sweeping lield 13 depends on many considerations known in the art of wave guides and coaxial cables. One preferable mode that can be utilized is a TM wave-which is a transverse magnetic lCC wave having no component of its magnetic force in the direction of translation of the wave along the wave guide. In order that the sweeping field 13 be most effective, the frequency of sweep is a function of the rate at which a leak tube 18 is lled.

A major problem in this particular art is the attaining of a desired uniform gas density within the housing 10. As shown, a gas diffusing means illustrated as the hollow cylindrical palladium or nickel leak tube 18 passes through the center of the housing 10 and receives a light ionizable gas such as hydrogen or deuterium from a gas supply tank 19 at its input end 20. In order to allow the gas to diiuse into the propulsion chamber, the leak tube 18 is maintained at an elevated temperature of the order of 400 C. As illustrated, the leak tube 18 is heated by a convenient means such as a coiled heater filament 22.

Additionally, the wall of the tube 18 can be partially lled with ferrite or doped with ferrite materials both to improve the configuration of the sweeping field 13 and to allow inductive heating of the leak tube 18. As is well known, the addition of a ferro-magnetic material to the palladium or nickel tube greatly increases its permeability so that the wave form across the chamber towards the center electrode is more nearly perpendicular to the electrode. In fact, it is preferred that the power` operating mode of the engine be so predetermined that a major portion of the heating, after initial energization be accomplished by the energy of the sweeping magnetic field 13. Usually a leak tube 18 of this type has a wall thickness of the order of ten mils.

In a system wherein the inner diameter of the chamber within the housing 10 is of the order of ten centimeters, the leak tube 18 has a diameter of the order of one centimeter. Thus the surface area of the leak tube 18 is a predetermined function of the volume to be filled. In this particular embodiment, the input pressure of the fuel gas supplied from the tank 19 may be regulated to be of the order of a few pounds per square inch so that the gas will ow from the leak tube 18 to the outer surface in a period of about thirty microseconds. Such rapid ow of the gas is accomplished primarily because the flow is from a substantial pressure into an almost complete vacuum. The average velocity of the gas ow through the evacuated chamber from the leak tube 18 is about four times sonic velocity for the conditions specified herein. With this velocity, the sweeping field 13 is utilized once each thirty microseconds to prevent interaction between gas particles.

Because of the fact that in the present invention the housing 10 is operated to be swept clean each time gas particles first reach the inner surface of the housing 10, there is a minimum interaction between individual particles, and minimum inherent longitudinal velocity of the gas. Moreover, the pressure (or gas density) is controlled by the rate of leak of gas from the leak tube 18. By controlling the pressure and temperature of the leak tube 18 the rate of leak of gas is maintained at a level which will provide a particle density of about 1018 particles per cubic centimeter. a

In an apparatus of this type some diiculty could be encountered in attaining a predetermined equilibrium temperature of the system. This problem arises for the reason that the rate of the escape of the gas out of the leak tube is a function of the tubes temperature, the tubes temperature in turn is a function of the energy of the ionizing electro-magnetic wave which in turn increases upon the increase of the gas density within the plasma chamber. Thus can be seen that there is in effect a chain reaction among the components whereby when more heat is generated more gas is released which in turn increases the energy of the wave, which in turn increases the temperature of the leak tube and so on. Such cumu- 3 lative operation is controllable by several rather simple expedients. In a most direct approach, we can provide for heat exchange cooling of the leak tube 18. However, in a somewhat simpler approach, we prefer to limit the power available to the field winding 12. Although-a direct power limit is feasible, we presently prefer to limit the frequency of the pulses as a function of the temperature of the leak tube 18. In order to accomplish this frequency control, a thermocouple 24 senses the temperature of the leak tube 18 and provides a signal to limit the frequency of pulses from the power supply 11 by any conventional means as well as to control the energization of the filament 22. By limiting the rate of the sweeping field 13 the interaction of the gas particles effectively reduces the leak rate and thus limits the overall energy expended by the power supply in driving the sweeping field 13.

Sweeping of ions at the high velocity contemplated results in the substantial energy transfer. In fact, the temperature in the region of the sweeping field 13 is of the order of 50,000 K. Such a temperature assures that all particles are ionized. However, if the engine is operating substantially continuously the average temperature within the housing will be of the order of 1,000 C. During such operating conditions it will be desirable to cool the palladium leak tube 18, a major portion of which is accomplished automatically by the admission of cool gas to the inner surfaces thereof. This cool gas receives substantial heat energy during its migration through the porous walls of the leak tube 18. In the event it is deemed necessary to operate engines at maximum load for extended periods, it is preferred to admit extremely cold, and in certain arrangements, liquified gas into the leak tube 18.

When an engine of approximately ten centimeters diameter is operated continuously with one pulse during every thirty microseconds and with the engine chamber approximately one meter long, the thrust will be of the order of five milligrams per pulse. Additional thrust is obtainable, usually at some loss in efficiency, by injecting into the system, downstream of the driver section, heavier atoms of various types.

Since the thrust is accomplished by wave propagation, the principles applicable to waveguides couplings and coaxial cable couplings will define the particular contigurations which are most efficient for admitting foreign matter. In FIG. 2 we have shown schematically one arrangement for admitting such heavier atoms where the driver section of the housing 10 is extended in length by the concentric arrangement therewith of cylindrical member 27. At the juncture of housing 10 and cylinder 27 there extends at right angles a stub hollow cylinder 26 connecting with the interior of the rest of the assembly. The stub member 26 is so designed to minimize transmission losses by matching impedance phenomena well known in this art.

A wide range of materials may be injected into the hot plasma downstream of the driver section 10 such as waste products, contamination from exhausted fuel tanks and the like, excess cooling fluids, thrust vector control fluids, etc. If the injected matter may be easily ionized a sweeping magnetic field may be arranged to exert accelerating forces directly on it by energizing coil 28 (FIG. 2). However, usually the primary accelerating forces on heavy atoms will be due to the bombardment thereon by already accelerated fuel ions.

Referring now to FIG. 3, we have shown a space engine constructed of three driving sections 12a, 12b and 12e similar to that illustrated in FIG. l. The sections are combined with a housing 10' arranged with unrestricted flow communication therebetween. In order to pulse these driving sections, we have provided these three sweeping eld pulse coils 12a, 12b and 12C. If the overall length of the housing 10' is made three meters, a sweeping voltage may be provided by a three-phase therefore, that our invention is not limited to the pare ticular form shown, and we intend by the appended claims to cover all such modifications which do not depart from the true spirit and scope of our invention.

What is claimed is: 1. A plasma generator and accelerator comprising: elongated housing means having an unrestricted exhaust port at one end thereof; an elongated leak tube arranged around the central axis of said housing, said leak tube being of a cross-seetional area of the order of V of the cross-sectional area of said housing; means for maintaining a supply of ionizable fluid particles of fuel within said leak tube; means for controlling the temperature of the leak tube at an elevated level to enhance leakage therethrough of the fuel at a rate creating within said housing a density of the order of 101 particles per cubic centimeter with substantially no reflection from the inner surface of said housing; and means for sequentially propagating electromagnetic sweeping magnetic eld from the closed end of said housing to the port thereof, with the rate of propagation of the sweeping field being of the order of 105 meters per second and with the energy of the sweeping field being sufficient to assure ionization of substantially all fuel particles. 2. A plasma generator and accelerator comprising: elongated cylindrical housing means having an unrestricted exhaust port at one end thereof; an elongated leak tube within said housing arranged around the longitudinal axis of the housing; means for maintaining a pressurized fuel gas in said leak tube; means for heating said leak tube to enhance leakage therethrough of gas particles at a rate creating within the housing a density of the order of 10lo particles per cubic centimeter; means for repeatedly propagating an electromagnetic wave from the closed end of said housing to the port, with the rate of propagation of the sweeping magnetic field being of the order of 105 meters per second and with the energy of the sweeping eld being sufficient to assure ionization of substantially all fuel particles; and means for controlling the temperature of said leak tube. 3. A plasma generator and accelerator comprising: elongated housing means having an unrestricted exhaust port at one end thereof; an elongated leak tube arranged along the major axis of said housing, said leak tube being of a crosssectional area of the order of V100 of the crosssectional area of said housing; means for maintaining a supply of ionizable gas particles within said leak tube; means for controlling the temperature of the leak tube at an elevated level to enhance leakage therethrough of the gas at a rate creating within said housing a density of the order of 1015 particles per cubic centimeter with substantially no reflection from the inner surface of said housing; and means for pulsing an electromagnetic sweeping magnetic eld from the closed end of said housing to the port thereof, with the rate of propagation of the sweeping field being of the order of 105 meters per second and with the energy of the sweeping field being sutiicient to assure ionization of substantially all fuel particles, said leak tube containing ferrite particles for shaping the sweeping field.

4. A plasma generator and accelerator comprising: elongated cylindrical housing means having an unrestricted exhaust port at only one end thereof; an elongated leak tube within said housing and arranged around the longitudinal axis thereof; means for maintaining a pressurized light-gas fuel in said leak tube;

means for heating said leak tube to enhance leakage therethrough of gas particles at a rate creating within the housing a density of the order of le particles per cubic centimeter;

means for repeatedly propagating an electromagnetic wave from the closed end of said housing to the port, with the rate of propagation of the sweeping magnetic field being of the order of 105 meters per second and with the energy of the sweeping field being sufficient to assure ionization of substantialy all fuel particles; and

impedance matched means for inserting particles heavier than the light-gas fuel into the accelerated ion flow downstream of the port.

5. A space engine comprising:

an elongated cylindrical driving section having an unrestricted exhaust port at only one end thereof;

an elongated leak tube within said section and arranged around the longitudinal axis thereof;

means for maintaining a pressurized light-gas fuel in said leak tube;

means for controlling the temperature of said leak tube to control the rate of leakage of gas therethrough;

pulse coil means for propagating an electromagnetic wave from the closed end of said section to the port with energy sufficient to assure ionization of substantially all fuel particles in said section; and

impedance matched means coupled downstream of said section for inserting particles heavier than the light-gas fuel into the accelerated ion ow to increase the thrust per pulse.

6. A space engine comprising:

an elongated cylindrical driving section having an unrestricted exhaust port at one end thereof;

an elongated leak tube centrally within said section, said leak tube containing a light-gas fuel;

means for controlling the temperature of said leak tube to control the rate of leakage of gas therethrough; and

pulse coil means for propagating an electromagnetic wave from the closed end of said section to the port with energy sufiicient to assure ionization of substantially all fuel particles in said section.

7. A plasma generator and accelerator comprising:

a plurality of elongated driving sections being aligned in unrestricted flow communication with each other and having an unrestricted exhaust port at one end thereof;

an elongated leak tube arranged along the major axis of said plurality of sections, said leak tube being of a cross-sectional area of the order of $400 of the crosssectional area of said sections;

means for maintaining a supply of ionizable particles of fuel throughout said leak tube;

means for controlling the temperature of the leak tube to regulate leakage therethrough; and

-sequentially operable pulse coil means for propagating an electromagnetic sweeping magnetic field through each of said sections toward the port, with the rate of propagation of the sweeping field being of the order of 105 meters per second and continuous throughout all of said sections and with the energy of the sweeping field being sufiicient to assure ionization of substantially all fuel particles, said leak tube oitaining ferrite particles for shaping the sweeping 8. A space engine comprising:

a plurality of elongated driving sections aligned to provide unrestricted flow communication therebetween and having an unrestricted exhaust port at one end thereof;

an elongated leak tube arranged along the major axis of said plurality of sections;

means for maintaining a supply of ionizable gas fuel throughout said leak tube;

sequentially operable pulse coil means for propagating an electromagnetic sweeping magnetic field through each of said sections toward the port, which sweeping field is substantially continuous throughout all of said sections and with the energy of the sweeping field being sufiicient to assure ionization of substantially all fuel particles; and

impedance matched means coupled downstream of the port for inserting particles heavier than the gas fuel particles into the accelerated ion fiow.

9. A plasma accelerator comprising:

an elongated driving section having an exhaust port at one end thereof;

an elongated leak tube centrally located within the driving section, the periphery of said leak tube having a porosity sufficient to provide for the escape therethrough of an ionizable gas fuel whereby the fuel is uniformly supplied to the driving section along substantially its full length;

a supply of fuel communicating with the leak tube; and,

pulse coil means propagating an electromagnetic field sequentially sweeping the length of the driving section, the energy of said field being sufficient to ionize substantially all the fuel within the driving section and to accelerate and expel the ionized fuel through the exhaust port.

l0. A plasma generator and accelerator comprising:

l a driving section having an exhaust port;

leak tube centrally located within the driving section, the walls of said leak tube having a porosity sufficient to provide for the escape therethrough of an ionizable gas fuel whereby the fuel is uniformly supplied throughout the driving section;

a supply of fuel communicating with the leak tube;

and

pulse coil means propagating an electromagnetic field sequentially sweeping the driving section, the energy of said field being sufficient to ionize substantially all the fuel within the driving section and to accelerate and expel the ionized fuel through the exhaust port.

References Cited in the file of this patent UNITED STATES PATENTS 2,578,009 Linder Dec. l1, 1951 2,826,708 Foster Mar. 11, 1958 3,069,344 Post et al. Dec. 18, 1962 OTHER REFERENCES Plasma Acceleration (Kash), published by Stanford University Press (Stanford, Calif), 1960 (pages 60-72 relied on).

Propulsion Systems for Space Flight (Corliss), published by McGraw-Hill Book Co. Inc. (New York), 1960 (pages 2l6 and 220-225),

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Classifications
U.S. Classification60/202, 417/49, 417/50, 310/11, 313/362.1
International ClassificationB64G1/40, B64G1/22, F03H1/00
Cooperative ClassificationF03H1/00, B64G1/405
European ClassificationF03H1/00, B64G1/40D