US2992345A - Plasma accelerators - Google Patents

Description

July 11, 1961 Filed March 21, 1958 S. HANSEN PLASMA ACCELERATORS 5 Sheets-Sheet l July 1l, 1961 Filed March 2l, 1958 S. HANSEN PLASMA ACCELERATORS 5 Sheets-Sheet 2 Miyag- July 1l, 1961 s. HANSEN 2,992,345

PLASMA ACCELERATORS V Filed March 2l, 1958 5 Sheets-Sheet 3 www4??? July 11, 1961 s. HANSEN PLASMA ACCELERATORS 5 Sheets-Sheet 4 Filed March 2l, 1958 www??? July 11, 1961 s, HANSEN 2,992,345

PLASMA ACCELERATORS Filed March 21, 1958 5 SheetS-Sheel'l 5 United States Patent 2,992,345 PLASMA ACCELE'RATORS Siegfried Hansen, 'Los Angeles, Calif., assigner, by mesne assignments, to Litton Systems, Inc., Beverly Hills, Calif., a corporation of Maryland Filed Mar. 21, 1958, Ser. No. 723,018 35 Claims. (Cl. 313-6`3) This invention relates to plasma accelerators, and more particularly to electromagnetic accelerators which are capable of accelerating an ionized. gas plasmato extremely high velocities and energy levels and at relaltively high iiow rates. .y q

As herein utilized the term plasma designates a volume of gas in which an appreciable percentage of the atoms are ionized, but which contains the detached electrons within the same volume so that the gas as a whole is electrically neutral. Except for mechanical rigidity, therefore, a plasma is very similar to a metal in its properties since the detached electrons remain uncombined for relatively long periods and can move about yat random within the bound-aries of the gas volume. Inn fact, it can be readily demonstrated that the electrical conductivity of 'a relatively highly ionized plasma can actually exceed that of such good electrical conductors as copper and silver.

It has been recognized by science that a gas accelerating method which produced both extremely high Vvelocities and large iiow rates would have a number of valuable applications. For example, one area of tremendous import for such a device would be its use as a concentrated heat source with the capability of producing extremely high and heretofore unattainable temperatures; as such a plasma accelerator could be utilized in various controlled thermal processes, such as for providing a controlled thermonuclear reaction. Another use for a device of this nature would be in a hypersonic windv tunnel for testing of high altitude vehicles, while still `a further conceivable use would be as a thrust producing device with high specific impulse to thereby provideva propulsion unit for inter-orbital space vehicles.

-In the prior art many devices have been developed for accelerating gas to extremely high velocities.l Perhaps the foremost of these is the Well known particle accelerator of the nuclear physicist, wherein small quantities of gas in the form of free ions are given repeated impulses by -an alternating current eld until a speed closely approximating the speed of light is achieved. Despite the high velocities which these devices achieve, however,

they are inherently limited to extremely low liow rates' by the fact that the free ionsvcreate a space charge which tends to cancel the accelerating field. f

Itl is also well known inthe prior art that relatively large quantities of gas can be accelerated to provide high l liow rates, as is done by thermal methods Vin internal combustion reaction motors wherein the random velocity of the molecules of a burning gas are converted to a directed velocity by permitting the gas to expand in a properly designed nozzle.

It will be recognized from the foregoing discussion that although these prior art -techniques may perform satisfactorily in numerous applications, they cannot provide both the high ow rates and extremely high velocities which science has been seeking for the particular applications enumerated hereinabove. Moreover, it is'equally apparent that these prior art techniques cannot be combined to provide the desired tlow rates concornitantly lwith high velocities.

Unfortunately, in these de-- vices the maximum velocity which the gas can attainis and reacts with the moving magnetic field in substantially.

Stillfanother technique known in the prior art for generating extremely high plasma temperatures involves the use of a gas filled toroid around which a magnetic eld winding is placed. According to this technique the gas in the toroid is ionized and a circulating .current of intense magnitude is theninduced therein, the circulating tures as'high asgive million degrees centigrade, it

limited by several serious disadvantages. Firstly, the

maximum temperature achievable thereby is limited byv radiation due to the high inter-particle relative velocities.

Secondly the gas'is trapped in the toroidal chamber and, cannot be emitted in high velocity output bursts. Finally, the fact that the temperature is achieved in `the center of the gas toroid by radial acceleration of the particles` toward.' e toroidal axis limits the practical usefulness of the reaction.

The present invention, on the other hand, providesl electromagnetic accelerators which combine the ladvantages of the several prior art techniques while overcoming their inherent limitation, thereby filling thev void which exists in the art.

magnetic accelerators which are operative to `linearly accelerate a volume of gas plasma through the use'of" electromotive principles whereby a moving magnetic field which is accelerating in space is employedto induce electric currents in the gas plasma which interact withv accelerating magnetic field, and are operable upon anannular or ringshaped plasma mass introduced at one end of vthe structure to produce accelerated plasma output bursts at the opposite end. Owing to the goodconduc-` tivity of gas plasma, the plasma mass entering the structure has circulating electrical currents induced therein,

the same manner as the rotor of an induction motor by moving 4after the advancing iield. Inasmuch as the magnetic iield is accelerating in lieu of moving at a constant velocity, however, the plasma mass is accelerated as .it advances through the accelerating structure, the velocity of the plasma lagging or slipping slightly with respect to the lield velocity to thus maintain the ionization of the plasma.

As will be disclosed in more detail hereinbelow, the

v accelerating structures of the various embodiments of the invention are termed either hard or soft, and either straight or convergent, depending upon the ultimate application in which the accelerator is to be utilized. More specilically, the terms soft and hard refer to the total acceleration imparted to the plasma, or stated dilerently, the velocity of the output plasma, a hard accelerating structure producing output bursts at higher energies and terminal velocities than a soft accelerator. The terms straight and convergent, on the other hand, refer to the shape of the accelerating structure and iield, a straight accelerating structure functioning to produce plasma output rings whose cross-sectional area is approximately the same as that of the input plasma mass, whereas a vcon-- vergent accelerating structure produces output plasma rings which are also accelerated radially inward and 'which therefore tend to focus at a point remote from the laccelerating structure.

In each of the several embodiments of the invention there is also provided a source of gas plasma, and a structure to produce the Arequisite accelerating field. In

Patented July 11, 1,9161l 'In accordance with the basic` :concept of the invention there are provided electrovelocities at relatively high ow rates.

apparatus for accelerating a gas mass to extremely high It isa further object of the invention to provide apparaf tus for linearly accelerating relatively large amounts of gas plasmato extremely high velocities.

Another object of the invention is'to provide electromagnetic accelerating apparatus'which employs electromotive principles for linearly accelerating af'gas plasma mass to extremely high velocities.

'Stilljanother object of the invention is to provide electromagnetic accelerating apparatus wherein a magnetic iie'ld` accelerating linearly in space is employed to induce electrical currents in an annular mass of gas plasma to thereby: produce an induction motor effect whereby the plasma mass follows after the advancing field.

The novel' features which are believed to be charac-A teristic of the invention, both as'to its organization'and rne'fthod 'of operation, together with further objects and advantages thereof, will be better understood fromftlie following description considered in'connection with the accompanying drawings in which several embodments of the inventon are illustrated by way of example. It is to be expressly understood, however, that the drawings are forfthe'purpose of illustration and description only, and are not intended yas a Vdefinition of the limits of the invention.

FIG. l is a block diagram illustrating the basic ele" ments .of a plasma accelerator, in' accordance with the present invention; I

FIG'. 2 is across-sectional view, partly in block diagram form, of a plasma accelerator illustrating the man ner in which the various elements thereof cooperate;

FIG. 3A is an isometric view of a shutter disk whichkmay be employed in theA accelerator embodiment of FIG. 2 for producing controlled bursts of an ionizable gas; t

FIG. 4 is a schematic diagram of an accelerator eld winding and the associated circuits which may *be employed for energizing the accelerator shown in FIG. 2;

"'FIG. 5 is a plan view, partly in section, of an accelerator field winding illustrating one form of construction' which may be employed therein;

FIG. 6 is a graph which is useful in illustrating one manner in which the accelerator of the invention may be employed to accelerate an annular plasma mass;

FIG. 7 is a diagrammatic view of an alternative ern-A bodimeut of a plasma accelerator, in accordance with the invention;

FIG. 8 is a graph illustrating the magnetic field winding distribution which may be utilized with the polyphase alternator employed for energizing the embodiment of FIG. 7; and

' FIG. 9 is a diagrammatic view of s-till another plasma accelerator according to the invention.

With reference now to the drawings, wherein like or corresponding parts are designated by the same reference characters throughout 'the several views, there is shown in FIG. l a; generalized block diagram of an electromagnetic plasma accelerator, according to the invent-ion, indicating the principal elements thereof and the manner in whichy they cooperate. Fundamentally the accelerator includes three basic elements, namely, a gas plasma source, gen-V In addition to the foregoing elements the accelerator will usually also include an associated exhaust system including -a chamber 16 and associated exhaust equipment y18 for maintaining the interior of the accelerating structure at a relatively low pressure to assure a reasonably long mean free path for the particles passing therethrough. As will be understood more clearly from the detailed t description set forth hereinbelow, the ultimate use to which an accelerator is put will in general determine whether an exhaust ,system is necessary, and what the capacity of the system should be. For example, if the accelerator is utilized as a generator of extremely high temperatures in a ground installation, exhaust pumps or the gas plasma, and in addition, to deliver the gas plasma tothe accelerating structure ondernand and in annularly shaped masses. As will become more apparent from the descrip-tion set forth hereinafter, gas source 20 may be a simple` source of gas at predetermined pressure, or may comprise a boiler for producing an ionizable vapor from a liquid, the nature of the gas source and the specific gas which is utilized being determined by the use to which the accelerator is to be put. For example, if an accelerator in accordance with the invention were to be employed in a thermonuclear reactor, the gas source would include means for supplying' latoms of deuterium, tritium or helium 3, whereas a simple air source would supply ionizable gas for a high altitude wind tunnel. In still other applications, on the rother hand, it may be desirable to vuse a gas whose molecules have a higher molecular weight, such as mercury vapor which may be generated in a boiler or the like. It should be noted here that it may also be desirable to employ a condensable gas such as mercury in still other applications of the accelerator where an exhaust system is required, since suitable condensers could then be utilized to reduce the capacity of the exhaust pumps employed in the system.

In a similar manner, the construction of the ionizing chamber and its associated interconnection with the gas source Will depend at least to some extent upon the ultimateapplication of the accelerator embodiment in which it is to be employed. More specifically, in certain applications, especially those where an associated exhaust system is required, it may be desirable to deliver the plasma to the accelerating structure in annular bursts through a suitable shutter mechanism, whereas in other applications it maybe sucient to deliver the plasma to the accelerating structure in a continuous hollow stream.

With reference now to FIG. 2, there is shown one form of plasma accelerator, in accordance with the invention, which employs a convergent accelerating structure 12' for generating extremely high temperatures at a predetermined point in an exhaust chamber 16 lby accelerating annular bursts of plasma received from the plasma source 10. In this particular embodiment of the invention the plasma source comprises a gas containing chamber 24 into which an ionizable gas is introduced through a valve 26 and is held at a predetermined pressure, and a combined annular nozzle and ionizing chamber formed by a conical ionizing electrode Z8 and an associated base plate 30 having a conjugate conical depression formed therein, electrode 28 being mounted adjacent the base plate by a plurality of insulating studs 32 at least one of which is hollow to admit an electrical connector 33 for applying an ionizing potential V1 to the electrode.

In addition to the foregoing elements the plasma source Yalsoincludes a mechanical shutter mechanism, generally designated 34, for intermittently passing bursts of gas izing electrode 28.

from chamber 1'6 into'the nozzle formed by electrode 28. As shown Yin FIG. 2, the shutter vmechanism comprises a metallic disk 36 which is driven by an electric motor 38 mounted within chamber 24, the disk including one or more apertures 40 drilled therethrough, as shown in detail'in FIG. 3. In operation these apertures are utilized toperiodically intercouple a pair of apertures 42 and 44v located in the right hand end of chamber 24 and in base plate 30, respectively, to thereby provide a conduit for introducing gas to the annular nozzle formed by ion- As further shown in FIG. 2, the shutter mechanism also includes an exhaust port 46 which is utilized to remove any gas which may leak past disk 36 when the disk is blocking aperture 42, thereby assuring that substantially no gas is delivered to the accelerating structure except through the apertures in the disk. In addition, the shuttermechanism further includes a magnetictransducer 48 which is mounted in base plate 30 adjacent the periphery of disk 36, the transducer being utilized to sense the ap- -pearance therebeneath of either of a pair of ferromagnetic slugs 50 which are inset in the periphery of disk 36. 'Asi will be described in more detail hereiubelow, the signals derived from the transducer are utilized to synchronize the energization of the accelerator with the operation of the shutter mechanism, or in other words, to synchronize the generation of the accelerating eld with the appearance of the plasma burst from the plasma source.v

Continuing with the description of the particular embodiment of the invention shown in FIG. 2, the accelerating structure 12 com-prises a glass or ceramic inner envelope member 52 over which a plurality of individual field winding sections 54'-1 through J.i4-n are stacked, the 4envelope member and the associated field winding sections having the configuration of a conical frustrum. As further illustrated in FIG. 2, the divergent end of envelope member S2 isV sealed against base member 30 by a suitable gasket 56, while the convergent endof the envelope member is sealed againsta flange S8 of eX- haust chamber 16 by a second gasket 60.

Before considering the detailed construction of the field ywindings employed in the embodiment of FIG.r 2, consider iirst the structure of electrical energy source 14 and the manner in which the energy source functions to energize the eld winding sections to provide the requisite accelerating field. As shown in FIG. 2 the electrical energy source comprises a plurality of timing circuitsv designated 62-1 through 62-n, and a corresponding plurality of associated pulse generators designated 64-1 through 64-n, respectively, each timing circuit and its associated pulse generator being electrically coupled to the accelerator tield winding section designated by the same reference suix. In operation, as will be disclosed in more detail hereinbelow, each timing circuit is responsive to electrical signals received from the previously described transducer 48 through a pulse forming network 66 for clocking off a predetermined interval at the end of which time the associated pulse generator is actuated to energize the associated field vwinding of accelerator 12. It will be appreciated, therefore, that the energization of the eld windings may be controlled sequentially to provide an accelerating field by merely employing a predetermined schedule of delay periods in the successive timing circuits.

With reference now to FIG. 4 there is shown a schematic 'diagram of a field Winding section 54, and one form of associated timing circuit 62 and pulse generator 64 which may be employed for controlling the energization thereof. In the schematic diagram of FIG. 4 the timing circuit employs what is known to the art as a cathode-coupled single-shot multivibrator for generating a lvariable delay, the multivibrator vincluding a pair of pentode vacuum tubes 66 and 68 whose cathodes are connected to ground through a common cathode resistor 69 and WhoseA anodesare eonnected to a source of anode voltage through a pair of plate resistors 7'0 and 71, r'espectively. The anode of tube 66 is also coupled to the control grid of tube 68'- through a variable timing capacitor 72, the control grid of tube 68 in turn being coupled to a source of bias voltage through a timing resistor 73. The control grid of tube 66, on the other hand, is coupled to an input terminal 74 through a differentiating circuit, generally designated 75, which functions to differentiate negative-going input signals and apply them to the control grid of tube 66 while blocking positivegoing input signals.

In operationtube 66 is normally conducting while tube 68 is' held below cut-oit by the bias through resistor 73. Upon the receipt of a negative-going input pulse tube 66 -is rendered non-conducting, the consequent rise in anode potential thereby ldriving tube 68 to its conducting state. In the customary regenerative manner tube 66 is then held cut-off by the current through cathode resistor 69 until the RC timing network formed by capacitor 72 and resistor 73 returns the control grid of tube 68 to its cutoi value at which time the conduction states of the tubes revert to their initial values.

of tube 68 in timing circuit 62 through a pulse differentiator generally designated 82. The circuit is completed by an anode resistor 84 connected to the thyratron and a tuned circuit load comprising a capacitor 86 and the primary winding of a step-up transformer 88 within iield winding section 54.

In operation the driving stage is normally held be-,

low cut-off and thus does not respond to the negative going signal developed in the timing circuit when the multivibrator utilized therein is switched to its astable state, this negative-going signal serving merely to switch the succeeding timing circuit to its astable state. However, at the end of the astable period when the timing circuit multivibrator again reverts to its stable state, the positive going pulse developed at the anode of tube 68 is differentiated by diierentiator 82 and functions to drive pentode 80 above cut-olf. Accordingly, a sharp positive pulse is developed by pulse transformer 78 for switching on thyratron 76 to thereby apply an output pulse to transformer 88, the tuned circuit formed by capacitor 86 and the primary winding of transformer 88 functioning to quench the thyratron after one half cycle of oscillation as the current through the transformer attempts to reverse.

Considering next the structure of field winding section 54, one end of the secondary winding of transformer 88 is connected to a source of high voltage, shown here to be 10 kilovolts, while the other end of the secondary is connected to a central spark electrode 90 which is positioned between and spaced from two additional spark electrodes 92 and 94. As shown in the embodiment of FIG. 4, electrode 92 is grounded through an associated :field winding 96, while electrode 94 is connected to a high voltage capacitor 98 which is in turn connected to a second source of high voltage through a limiting resistor 100, this latter voltage being shown here as 20 kilovolts.

Before describing the operation of the iield winding section it should be noted that the arc gap spacing between electrodes 90 and 92 is made sufficiently large so that the gap will not arc over at the voltage applied to the secondary of transformer 88, in this illustrative instance l0 kilovolts. In a similar manner, the arc gap spacing between eleotrodes 90 and 94 is made sufficiently large so that the gap will not normally arc over at the voltage idifferential between 20 kilovolts and 10 kilovolts, but will As will be recognized by. those Vskilled in the art, the period during which tube` 68f arc overif subjected to a voltage approaching 20 kil'or volts.

. In operatiomtherefore, capacitor 98 will be charged through Vresistor 100 to substantially 20 kilovolts, which is itslquiescent operating voltage. Y Upon the application of a pulse to step-up transformer 88, thereafter, spark electrode 90 is driven to a still higher voltage at which electrode 90 arcs over to electrode 92, the low resistance path formed by the ions in the arc thereby placing substantially 20 .kilovolts across the gap between electrodes 90 and 94. Consequently an arc is also drawn between these lat-ter twoelectrodes, thereby closing a low impedancerdischargerpath through field winding 96 for capacitor 98.

It should be noted at this point that field winding 96 is preferably a single turn conductor in order to minimize the inductance thereof, whilecapacitor 98 preferably has a small an inductance as feasible., The lreasons for this preference will be best understood from the operational description of the plasma accelerator of the invention as set forth hereinafter. It may be noted at this point, however, that the storage capacitor and the inductance of the discharge path for each field winding form a" tuned circuit resonant at a preselected radio frequency., In order to generate the strongest magnetic field within 'the accelerator at the selected frequency, it is clear that the largest feasible current should flow through the field winding, which in turn means that the storage capacitor must be relatively large while the charging voltage should be as high as practical. Since the resonant frequency ofV a series` tuned circuit is an inverse function of the product of inductance and capacitance, it follows that for any given frequency the inductance must be minimized if capacitance is to` be maximized. Moreover, since the surge impedance of a series tuned circuit is a direct function of inductance and an inverse function of capacitance, it follows that a small inductive reactance coupled with a large capacitance will also minimize the surge impedance presented to the discharge of the capacitor, thus further serving to maximize the current surge at the selected frequency.

It is also important to note at this point that while electrical energy source 14 in FIG. 2 is shown to include only the timing circuit and pulse generator associated with each field winding, the electrical energy source actually includes the pulse transformer, spark gap electrodes and storage capacitor shown as part of field winding section 54 in FIG. 4. The purpose in describing these elements as part of the field winding section, as will be understood from the description of FIG, 5, is that in practice it is preferable to combine these elements with the field winding per se in a mechanically integrated package in order to minimize the inductance of the discharge path through the field winding.

Referring now to FIG. 5, there is shown a cross-sectional view of a typical field winding section 54 illustrating one manner in which the various elements thereof may be packaged to minimize the inductance of the field winding circuit. As shown in FIG. the field winding per se comprises a relatively large single turn conductor 96 which is imbedded in a suitable insulating material 102, which may be an epoxy resin, for example. In addition the field winding is surrounded by a conductive shield 104 which may be constructed to nest with the shields on the adjacent field windings as shown in FIG. 2, and which functions to suppress the formation of an external field and thereby reduces the total inductance of the winding.

Continuing with the description of FIG. 5, one end of field winding 96 is brought out radially through a funnellike -member 106 which is brazed or otherwise afi'ixed to shield 104, this end of the field winding being connected directly to Vspark gap electrode 92. The other end of the field winding, on the other hand, is grounded to a tab 108 which depends into the insulating material from member 106. Spark gap electrode 94, in turn, is con` nected directly to an insulated terminal 110 of the high voltage capacitor 98 whose outer shell forms the second capacitor terminal and which is grounded to member 106 through a cylindrical sleeve 112. The electrical connection to the high voltage source employed for charging capacitor 98 is also made to insulated terminal 110, as shown in FIG. 5, through an insulated terminal 114 mounted in a suitable aperture in the periphely of sleeve The structure of the field winding section is completed -by pulse transformer 88 the secondary winding of which is pot-ted around a core 115, the ends of the secondary Winding terminating in a pair of arms extending outwardlyfrom the core. As shown in FIG. 5, the left arm is held in place by a bracket 116 affixed vto shield 104, while the right arm extends through an aperture in sleeve 112 and is held in position thereby, the central spark gap electrode being mounted directly to'the secondary winding of the transformer. Finally, the primary winding of the pulse transformer is provided by an insulated conluctor 118 which is merely passed around theY core of [the transformer.

Returning now to FIG. 2, consider the manner in whichjthe plasma `accelerator of the invention operates to accomplish the desired function. Assuming that exhaust chamber 16 has been evacuated previously, rotation of shutter disk 36 by motor 38 functions to adrnit periodic bursts of gas from chamber 24 into the combination ionizing chamber and nozzle formed by conical electrode 28 and base plate 30. At this point a relatively large 'number of the gas molecules in each `burst of gas areV ionized by the ionizing potential applied to electrode 28, thereby forming a plasma mass which ows into the accelerating structure as an annular plasma mass or ring traveling at thermal velocity.

IConcomitant-ly with the generation of each plasma ring a synchronizing signal is transmitted to electrical energy source .14 and therein functions to actuate timing circuits 62-1 through 62-n which in turn function to energize their associated eld windings in sequence and in accordance with a predetermined schedule of delay intervals. Thus as the annular plasma mass approaches the field winding of field winding section 54-1, pulse generator 64-'1 is actuated yby timing circuit 62-1 to fire the arc gap in field winding section 54-1, thereby generating an extremely strong magnetic field around its associated field winding.

Consider now the effect of the build-up of the magnetic field upon the annular plas-ma ring which has just been introduced into the accelerating structure. Since the electricaly conductivity of a relatively high ionized gas plasma can actually exceed that of such good conductors as copper and silver, itis apparent that the plasma ring will act as an electrical conductor moving in a magnetic field, and thus a circulating electrical current will be induced therein. It may be noted here that the relative movement between the plasma ring and the magnetic field which serves to induce these circulating currents is principally a function of the movement of the rapidly expanding magnetic field rather than the initial velocity of theentering mass of plasma which is moving at a relatively Vlow velocity. It should also be noted that current iscarried by both electrons and ions moving in opposite direction, the electron current predominating.

The current induced in the plasma ring is in turn operative to produce several different effects. f Firstly the current will generate a toroidal shaped magnetic field of its own surrounding the plasma ring, this field reacting with the current in the ring to generate a pinching force which tends to decrease the cross-sectional area of the plasma ring. This phenomenon will be recognized by those familiar with gaseous discharge phenomena as the Well known pinch effect.

Secondly the current in the plasma ring will react with the magnetic field generated by the field winding to create,Y

an accelerating force operating on the plasma mass to thereby accelerate the plasma toward the exhaust chamber. Finally,'the current flowing in the plasma ring and the attendant inter-particle collisions will serve to maintain the ionization of the plasma ring, thereby maintaining'the excellent conductivity thereof.

As the plasma mass thereafter increases in velocity, the remaining field windings are energized in sequence in accordance with the predetermined schedule of delays, and thereby function to produce an accelerating field through the accelerating structure, the field reacting withl the current in the plasma mass to accelerate the plasma continuously until the plasma is ejected from the accelerating structure into the exhaust chamber 16 at a terminal velocity which is dependent upon the acceleration imparted thereto and the period through which lthe accelerating force is applied. Meanwhile any tendency of the current yto decrease in the plasma ring while it is being accelerated will -be accompanied by slippage of theA plasma with respect to the accelerating field, since the accelerating force applied to the plasma ring is` a direct function of the current in the ring. Any slippageiof thev accelerating plasma ing with respect to theaccelerating field, however, will obviously tend to increase the currentflowing in the plasma ring and will thus tend to in-l crease the accelerating force acting to increase the velocity of the plasma mass as it moves through the accelerating structure. v

It will -vbe recognized from the foregoing generalized description of operation that the manner in which the plasma ring follows the moving field through the acceler- -ating structure is analogous to the manner in which the rotor of an induction motor follows after the advancing field generated -by the stator thereof. However, there are two important distinctions between the operation ofi an induction motor and the plasma accelerator of the invention. Firstly, the field in the plasma accelerator of the invention is moving at an ever increasing velocityk due to the acceleration thereof, while the field in an induction motor moves at a constant velocity. Secondlyg. the accelerator of the present invention imparts a sub-*1 stantially linear movement to an annular conductivel plasma, while `an induction motor imparts rotational movement to a plurality of linear conductors.

`Considering now the operationV of the plasma accelerator of FIG. 2 in more detail, there is shown in FIG. 6 a composite graph illustrating the time relationship between field winding energization, plasma ring position, plasma ring velocity and plasma ring acceleration for a plasma ring of preselected mass moving in'anaccelerating field of predetermined magnitude. Before describing the various curves it should be noted from the ordinate scales that only the first l5 field windings of a plasma accelerator are here taken into consideration,

each field winding being separated from adjacent fieldl windings by 2.1/2 centimeters taken along the axis of` the accelerating structure. units shown on the left hand ordinate scale apply to pos1- tion, velocity and acceleration of the plasma ring, the

Kappropriate scale factor for each function being set forth adjacent the corresponding curve. i

Recalling now that the plasma ring enters the accelerating structure at thermal velocity, which will Vcorrespond'` approximately to sonic velocity, it will be recognized' thatA the initial plasma velocity is negligibly small on the'` velocity scale of FIG. 6. dn addition, it is readily ap-' parent that until the first field Winding is energized the acceleration forces acting upon the plasma ring are sub-. stantially zero, since only a relatively small decelerating force due to friction and inter-particle collisions is acting upon the plasma.

When the first field Winding is energized at time. to.. therefore, a relatively large amount of the energy in therV magnetic fieldgenerated vthereby is employed to inducci-n It should also be noted that theV ldifferent times and the fact that change ink plasma position in the accelerating structures are both' relatively'small during this initial period immediately after feldwinding 54-1 is energized and beforey fieldwinding54-Z is energized.

' VReturning now to FIG. 6, it will be seen that the second field ,winding isrenergized shortly after the energza' tion joffthe-rst field winding whilethe position of the plasma ring has moved onlyy a relatively short distance,`

andltha-t the third, fourth and fifth field windings are also energizedin sequence before the plasma ring has movedv tolta` positionimmediately -Vunderthe second field winding.V

In fact itgwilljgbe seen, fronithe acceleration curve -and field jwindingenergization schedule that the accelerating force 'actingV on the annular plasmamfass continues to increase'as each oftherst seven field windings is energized,

the-,acceleration thereafter remaining constant at substantiallyV 17x10? meters/secl l It should be noted 'at this point that the accelerating field employed for moving the annular plasma massat anever increasing velocity through the accelerating structure-may' be generated in practice by energizing the field windings in, afsequence which appears almost linear withV respect` to time, as s howngby the energizationischedule OfFIG, 6. 4 T o explain this apparent anomaly it is necessary y,to consider the shape of the accelerating field and; themannei-in ,whichthie energization of the field windingsy functionsY to maintain the desired field configuration.

..More specifically, itmay-be shown analytically thatth'e plasma; ring preferably. should be located at all times "in` aplane Where the magnetic field vector adjacent the plasmarlring-is-:substantially normal to the sides of the accelerating-structure, since the accelerating forceV acting at' each point on the plasma will fact orthogonal lto the plane ofthe accelerating field vector `and plasma current at that point. It has been found that a moving field 'having this desired configuration may be generated by ltuning the successive field windings to successively higher resonant freguencieaand then energizing each successive field windlng after a delay which is only a relatively small portion" of they oscillation period of the'preceding field winding. The field windings will thus produce a composite magnetic field Awhich moves as va function of the phase and frequence difference `between successive windings, or in other words, which moves as the component of magnetic field contributed by each field winding varies with respect to that contributed by adjacent field windings owing to the= fact that the different field windings are energized at the field windings are tuned to successiyely'higher frequencies.

It should be noted here that the resonant circuits of the field windings function as damped ringing circuits after they have been energized, the current reversal in the earlier field windings dueto this ringing phenomena" producinga magnetic field component which interactsV with the magnetic field components generated by succeed-l ing field windings' to produce the desired normal field pattern for accelerating the plasma ring. It should be further noted that when the rst field winding alone has been energized, the desired radial field pattern is simulated in part by a magnetic field image produced by eddy currents induced in base plate 30 of FIG. 2 by the accelerating field. n

Returning again to the curves of FIG. 6, it will be seen that after the desired circulating current has been established in the plasma ring, the acceleration remains relatively contant as previously described and the position .of the plasma ring advances tvery nearly in accordance 1l with the sequential energization of" the ffeld windings cept Vfor a small amount of slippage .necessary Y"to mamtain the circulating currents inthe plasma ring. 'Ilfor'illus-r trate this latter point in Imore detail, it willbe'nted th'atf the-time lapse between the energization/foflthe -eighth and ninth field windings is approximately .5 microsecond, which correspond to a velocity of 50,000 meters 'fperlsecond for field windings spaced 2.1/2 centimeters apart, "while the time lapse between the energization of the `fourteenth and fifteenth windings is approximately .28 microsecond which corresponds to a velocity of 89,000 meters `per sec'- ond. As shown by the velocity curve, on the other hand, the `average velocity of the plasma ring in the interval between the energization of the "eight and ninth 'field windings is approximately 48,000 meters per second, and 5increases to an average velocity of approximatelyr82,000 meters/ second during the 'interval between the energization of the fourteenth and fifteenthfiield windings. Hence, the'pl-as'ma is accelerated toa velocity approximately one'- thousandth the velocity of light, or, in other words, to arv'elocity approaching 4the Vspeed of light. It -is clearfof course, that the velocity of that plasma canY be easily increased or decreased by merely increasing ordecreasing the length of acceleration. Therefore, the plasma velizy.:- ity at the accelerator output can be more correctly Vdescribed as being greatly in excess of sonic velocity. p

Consider now the various interrelated'parame'ters which should be considered when designing a Vplasma','accelerator in accordance with the 'present invention. It should iirst be recalled from elementary physics 'that the force acting upon a current carrying conductor `in a magnetic'Y field is directly proportional to 'the product of 'the mag-' netic field strength and the current flowing in the con-v doctor. Accordingly it follows that maximumaccelera-j tionfora plasma ringV of vgiven mass would'beachicved by maximizing both field strength andthe cur-rent flowing in the plasma. desired to provide uniform acceleration after Ithe'desired circulating current has been induced in the plasma, 'the strength of the accelerating magnetic field 'operatioxjon the plasma should also be uniform.

In general it may Yb'e stated that the `rriagnetic sh'ould be made as strong as practical for several reasons. Firstly, the stronger the magnetic field, the 'less cum-ent which must be sustained in 'the plasma mass to; 45 achieve I'a"specified acceleration. Minimization of the.

current flowing in the `plasma ring in turn will lrequire less slippage of lthe plasma with respect to lthe accelerating field -in order to maintain the plasma current, thus also signifying that the acceleration can be applied for a longer period and that there will be a smaller power 'loss through heat in the plasma. Y t

A second reason for employing' the Astrongest practical magnetic field vrelates to the mass of ythe plasma which may be accelerated in each plasma burst. It is readily apparent, of course, that for a given terminal velocity the maximum output energy will be delivered by a plasma -ring whose mass is maximized. In general 'it will Ybe recognized that if all other factors such vas field strength and field acceleration `are held constant, the larger the mass of the plasma, the Vlarger the current required to` maintain the accelerating force and hence the larg'cr'the slippage of the plasma with respect Ito the accelerating` field` On the other hand, it `is also aparent that the `use of a stronger accelerating magnetic field will permit la larger mass to be moved at the desired acceleration with` out increasing the `value of the circulating current in the plasma.

It will be recognized 'from the foregoing ydiscussion that acceleration is directly proportional tonfi'eld strength and plasma current and is inversely proportional'to plasma mass, or in other words In addition it also follows that if `it is MKS system. lt is important to note, however, that while each of these parameters may appear equally significant in its effect on the output energy deliverable from a plasma accelerator as herein disclosed, it may be readily demonstrated by analysis that increased acceleration and output energy is best obtained by -an increase in field strength. Recalling then the discussion hereinabove of the field winding section shown in FIG. 5, it will now be appreciated why it is preferable to minimize the inductance of each field winding, to employ relatively lange discharge capacitors, and to operate at as high a voltage as practical, since the proper selection of these Values will provide maximum field strength within the accelerating structure while still enabling the eld windings to resonate at the desired frequencies.

Considering now the physical dimensions of the accelerating structure it will be appreciated that there is a considerable degree of latitude permitted in selecting the length and cross-sectional area of the accelerator. For example, if one assumes a given number of field windings per unit length of the accelerating structure, it is clear that a longer accelerating structure will provide a longer plasma transit time to achieve a desired terminal velocity,`

and hence for a given constant field strength less circulating currentneed be induced in the plasma ring to achieve the desired velocity. that the field strength has been made as high as Apractical Iand that the field windings have been placed as close together as practical, the acceleration engendered thereby can be applied for a longer period of time to thereby produce a higher terminal velocity merely by making the accelerating structure longer so that additional field windings may be employed. It should be kept in mind, however, that for a longer laccelerating structure it may be necessary to increase the pumping capacity of the exhaust chamber in order to insure that stagnant lgas does not accumulate in the accelerator to a point where it materially increases the pressure therein. In general it may be lstated that the pressure within the accelerating struc- Iture should be maintained below l l0-4 millimeters of mercury if the accelerator is to be used for generating relatively high temperatures.

Insofar as the cross-sectional area of the accelerator is concerned, on the other hand, it will be appreciated that the field strength for a given field winding current will be maximized by minimizing the accelerator crosssectional area. It must also be kept in mind, however, that the mass of the plasma in each burst must also `decrease as cross-sectional area is decreased, and that the field which produces pinch effect in the plasma will also tend to expand the plasma ring if fthe diameter of the plasma ring is made too small. This latter effect will be discussed in more detail hereinbelow.

As described previously, the phenomenon known as pinch effect is produced by the circulating current flowing inthe plasma mass, this current producing a toroidal field which envelopes the plasma. and reacts with the current in the plasma to produce a force which acts to reduce the cross-sectional area of the annular plasma mass. Thus as the circulating current is initially induced inthe plasma mass, the cross-sectional area of the plasma starts to decrease and continues .to decrease thereafter While the circulating .current increases to the desired value. Thedecrease in plasma cross-sectional area is in .turn accompanied by yan increase in the internal pressure in the plasmatring, this latter force opposing the pinch effect. Accordingly, for a given circulating current the plasma ring ywill be pinched in an exponential manner until the internal pressure forces andthe forces pinching the plasma are substantially equal. Y

It is extremely important to note atvthis point tha plasma :accelerators constructed according to theteachings ofthe present invention employ a moving 'soleiy On the other hand, if one assumesY 13 plasma, and that the pinch elect is merely a result of the circulating current in the plasma rather than the source by which the particles are accelerated. 'Ihus an output burst of plasma may be emitted at a velocity which is an appreciable fraction of the speed of light while the relative velocities of the particles Within the plasma with respect to each other is relatively low.

It should be Ifurther noted, however, that the pinch elect is a useful phenomenon if it is desired to employ a plasma accelerator according to the invention for generating extremely high temperatures, since the pinch can `be-` employed for concentrating the output plasma bursts. More specically, it may be shown that the effective temperature generated by the collision of a high velocity plasma with an object is inversely proportional to the area which the plasma strikes, or in other words, is inversely proportional to the projected frontal area of the plasma at the point of impact. Since the pinch effect will tend to reduce the cross-sectional area of the plasma ring, it follows that it will also function to reduce the projected frontal area of the plasma ring if it is assumed that the diameter of the plasma ring is either constant or decreasing in size. It should be pointed out that in practice the pinch field around the plasma will also tend to increase the diameter of the plasma ring since the iield at diammetrically opposite points on the plasma mass opposes itself. However, this tendency may be more than overcome by utilizing a convergent accelerating structure since the acceleration imparted to the plasma will then resolve into an axial component and a component directed radially inward, this latter force electively obliteratingthe tendency of lthe plasma to expand in diameter from the pinch effect. It is then clear yfrom the foregoing discussion that in determining the current which it is Adesired to have circulating in the plasma, consideration should be given to the pinch eitect which will be produced thereby, since the pinch eifect will influence the effective temperature which the plasma can produce upon striking a target. Y

Still another factor which should be considered in the design of a plasma accelerator in accordance with the present invention is the eiect of plasma mass and duty cycle on the exhaust capacity of the system and the available electric power. More specifically, it will be recognized that the frequency at which plasma bursts are emitted and the mass of each burst should be selected in view of the capacityof the exhaust pumps in order to maintain a suliiciently low pressure in the accelerator so thatplasma bursts mayflow therethrough unimpeded. Insofar as the input power consideration is concerned, on the other hand, thefrequency at Iwhich plasma bursts enter the chamber must also be suiiiciently low to enable the iield Winding storage capacitors to charge to the desired value of potential between successive energizations thereof.

In order to illustrate the relative magnitudes of the various interrelated parameters discussed hereinabove, the following table sets forth the specifications of an experimental high-temperature plasma accelerator designed in accordance with the eachngs of the invention.

Number of :field windings 160. Durationof acceleration of each burst 20 microseconds. Duty cycle 0.0012. Average acceleration 1O9 meters/sec?. Average mechanical force newtons. Average accelerating magnetic eld 0.5 weber/m2.

.14 Table I Continued Average ring current in plasma 200 amp. P l a s m a temp erature after pinch 1390 K. Plasma pressure after pinch 2.91 newtons/m-2. Pinch radius 1.48X10-2 m. Pulse power demand 500 kw. Average output power `600 watts. Rate of heat generation in ring- 17.35 kw.

interrelated parameters discussed previously. Moreover,V

it will be recalled that the plasma accelerator may be employed inapplications other than in the generation of extremely'high temperatures, in which instances it may be desirable to produce a higher mass flow rate at a lower terminal velocity, for example.

With reference now to FIG. 7 there is shown a diagrammatic View of another embodiment of a plasma accelerator, in accordance with the invention. In this particular embodiment of the invention plasma source 10 comprises a chamber 20 containing a condensible gas, such as mercury, which may be vaporized by a heater 200, an'ionizing chamber 22 including an electrode 202 for ionizing the vapor received from chamber 20, vand an annular nozzle 204 which delivers an annular plasma mass to an accelerating structure 12 which is energizable from an electrical energy source 14, which -in this inf stance comprises a polyphase generator or alterna-tor.

As shown in FIG. 7, the accelerator structure comprises a hollow cylindrical outer member 206 and a cylindrical inner member 208 concentric therewith, each of these members including a plurality of longitudinal laminates of ferromagnetic material which are stacked circumferentially against an associated cylindrical supporting element. The individual laminates also include a plurality of slots spaced along the length thereof, the slots in each laminate cooperating with the corresponding slots in the other laminates in the associated stack to provide grooves for receiving the iield windings. For purposes of simplicity the field windings are shown in FIG. 7 as a plurality of individual conductors adjacent the surfaces of members 206 and 20S. However, as will be understood from the description hereinbelow of FIG. 8, each eld winding slot may actually include a plurality of conductors energized from different phase outputs from the polyphase generator which constitutes the tield winding energy source.

Assuming now that three phase excitation is to be employed for energizing the accelerating structure, it will be recognized that the accelerator iield windings should be divided into three groups corresponding to the three phase excitation, each group of windings being connected to and energized by the corresponding alternator phase. With reference now to FIG. 8, there is shown one manner in which the Winding turns in each eld winding group may be distributed longitudinally along the accelerator axis to provide a uniform accelerating field with three phase sinusoidal excitation. As illustrated by the graph, the density per unit length of the field winding turns associated with each exciting phase varies as a constantly accelerating sinusoid, the polarity of the density curve for each phase indicating the direction of energization of the associated winding turns. For example, at the longitudinal distances designated 210 and 212 n FIG. 8 the density of the winding turns excited by phase 1 is at a maximum, but the current owing through the turns at .distance 210 is opposite in direction to the current ow- Morek 15 ing through the turns at distance 212. Conversely, the windings excited by the second Vand`ft-hird -phases have a turn density 'of only one half the maximum value at points 210 and 212, and are pole'd opposite to the phase 1 windings at the same points.

It should be here noted that the field windings on inner member 208 of FIG. 7 are energized in the same manner as the field windings on the outer member 206, or in other words, that the three groups of phase windings are distributed and polarized in substantially the same fashion on both the inner and outer members which form the accelerating structure. It will thereforebe recognized that excitation ofthe three field windinggroups from asource of three phase sinusoidal power will produce a composite magnetic field which accelerates through the accelerator structure in accordance with the distribution of the field winding turns. Moreover, the amplitude of the advancing field, as viewed from any fixed point along .the :accelerator during one input power cycle, will reach a maximum on two occasions 180 apart in time, the sense of the eld reversing itself intermediate the points of maximum intensity. Accordingly during each input power cycle -two annular plasma masses may be accelerated through the accelerating structure by .the moving field generated thereby, the direction of the circulating current flowing in each annular plasma burst being opposite to that of the current flowing in the preceding burst and that which will ow in the ysucceeding burst. v

It should be kept in mind, of course, that while only one accelerated winding turn distribution cycle is shown in FIG. 8, an accelerator Vstructure of the form shown in FIG. 7 could actually .include several continuously accelerating turn distribution cycles. It should be noted, however, that ytwo .accelerating plasma masses will be moving simultaneously through the accelerator for each accelerated turn distribution cycle of the field windings unless an appropriate shutter mechanism is employed to enter plasma bursts selectively into the accelerator. It should be noted further that the frequency of the input energy from the polyphase generator should be selected in view of the ultimate application of the accelerator to provide the flow rate and terminal velocity desired. lSince alternator structures capable of producing relatively high output power at frequencies up to and beyond one hundred kilocycles are well known in the induction heating and radio transmission arts, further description of the polyphase generator used for energizing the plasma accelerator of F IG. 7 is considered unnecessary.

Considering now another of the operational distinctions embodied in the plasma accelerator of FIG. 7, `it will be recognized that the use of a plasma mass generated from a condensible vapor may be advantageous in several different circumstances. For example, if the -accelerator is employed in conjunction with an exhaust system, a condensing mechanism may be utilized for condensing :a portion of the spent plasma to thereby reduce the pumping capacity of the exhaust system. If, on the other hand, a plasma accelerator as herein disclosed were to be employed as a propulsion unit for a space vehicle, the use of a relatively heavy condensible gas, such as mercury vapor, would simplify fuel storage without otherwise affecting the high impulse of the system.

It is apparent from the foregoing description that still other forms of plasma accelerators embodying the principles herein disclosed will readily suggest themselves for use in still other applications. For example, there is shown in FIG. 9 a diagrammatic view of an alternative form of plasma accelerator, in accordance with the invention, which may be utilized as a hypersonic wind tunnel for simulating Mach numbers of the order of two to twenty at pressures equivalent to the altitude range from 100,000 feet to 200,000 feet. For this particular application the obvious choice of gas to be accelerated is air which is delivered tothe accelerator structure through an V.ie

input Ymanifold 220, an ionizing chamber 22, and an expansion nozzle 204.

As shown in FIG. 9, accelerator structure 12 forthis particular embodiment of the invention has the configuration of a truncated cone so that the plasma will acquire an inward velocity component and converge at a .focal area within an exhaust system, not shown, which 4is the test region of the wind tunnel. the accelerated gas closely approximate undisturbed air, it is clear that the gas mass delivered by the accelerating structure should contain a relatively low percentage of.

accelerator with excess gas at the input thereof and byv utilizing arelatively lowv specific acceleration, since underk these conditions the gas will separate into regions of relatively high ion density which ride the magnetic field phase front of the accelerating field, as described hereinabove for the plasma accelerators of FIGS. 2 and 7, and regions of low ion density which are pushed through the accelerator by the regions of high ion density acting yas pistons.

In order to illustrate this latter application of a plasma accelerator according to the invention, the following characteristics are set forth as typical design parameters of a hypersonic wind tunnel for simulating `air movement at Mach 20 at an equivalent altitude of 200,000 feet.

T able II Accelerator:

Output density 4.10)(10-4 kg./mete`r3. Output pressure 3.73 X 10-4 atm. Output temperature 349'degrees K. Output velocity Mach 20=20 375 :7500 meter/ sec. 'Output mass 3.07)(10v2 lig/sec. lOutput volume 75 meter3/sec. Output area 1 102 meterz. Accelerating power 1020 kw. Heating power (122 K.349 K.) 8.5 kw. Ion density in rings 99.1%. Average ion density 17%. Exciting frequency 10 kilocycles. Mass of each `gas ring .1.53 X10-6kg. Disassociated charge in each ring 1.7 coulombs. Ring current 32.8 amperes. Electron drift speed 10.5 meters/sec. at

0.175 meter diam. Ring voltage 3.72)(10*4 volts. Power dissipated in each ring -1.22 102 watts. Peak flux density 0.07 Weber/meterz. Average flux at ring 0.05 weber/meter2. Core losses 1.7 watts/'1b. Average acceleration 1.07)(106 meters/sec. Duration for 7500 meter/sec. output 6.38 103 sec. Length of accelerator 26.0meters. yNumber of rings 127.6.

Power dissipated in rings 1.43 watts.

Expansion nozzle (input to accelerator):

Expansion ratio 40:1.

Input temperature 350 degreesK.

Input pressure 1'.492 10f2 atm. Input density 1.49 l02 kg./meter3. Output temperature 122 degrees K.

Output pressure 3.73 X10-4' atm. Output density .,1.07 1,0-3 lig/meter?. Output velocity 676 meters/ sec. Output mass .3.07 102 kg./sec. Output volume 28.7 metersff/sec. Output area 4.24)(10*2 metersz.-

Since it is desirable that 1 7 Y Table II-Continued Associated equipment: A

Total cooling capacity 1122 kwa-:2.68 kilocal./

sec.=1065 B.t.u./sec. Pump capacity 75,000 liters/sec. at

0.28 mm. Hg.

It should be clear from the foregoing discussion that still other alternative embodiments of the invention may be devised without departing from the basic concept of the invention as herein set forth. Accordingly it is to be expressly understood that the spirit and scope of the invention is to be limited only by the scope of the appended claims.

What is claimed as new is:

1. A plasma accelerator for producing a gaseous discharge at high velocities and liow rates, said accelerator comprising: a source of an ionizable gas; an ionizing chamber coupled to said source for receiving said gas and for ionizing at least a portion thereof to produce a gas plasma; a tubular linear accelerating structure, said accelerating structure including a plurality of field windings disposed along the length thereof; a source of electrical energy coupled to said accelerating structure for energizing said field windings, said field windings being positioned and energized relative to each other to produce an accelerating magnetic field therethrough; and means for introducing gas plasma into said accelerating structure in an annular mass, said annular plasma mass responding to said accelerating magnetic field by accelerating through said accelerating structure after said magnetic field.

2. The plasma accelerator defined in claim l wherein said source of an ionizable gas includes a chamber containing mercury, and means for vaporizing the mercury to produce an ionizable mercury vapor.

3. The plasma accelerator defined in claim 1 wherein said source of an ionizable gas includes an input manifold for introducing said gas to said ionizing chamber.

4. The plasma accelerator defined in claim l wherein said ionizable gas includes molecules of at least one of the elements duterium, tritium or helium 3.

5. The plasma accelerator defined in claim l wherein said ionizing chamber includes an ionizing electrode, and means for applying an ionizing potential thereto.

6. A plasma accelerator for producing output bursts of gas plasma at a relatively high terminal velocity, said accelerator comprising: a straight tubular member having first and second ends; a plurality of field windings disposed around said tubular member along the length thereof; means for electrically energizing said field windings to produce a magnetic field within said tubular member moving at a continuously increasing velocity from said first end to said second end; and means for introducing gas plasma into said first end of said tubular member in annular input bursts, each of said input bursts having a circulating current induced therein by the action of said magnetic field, said circulating current reacting with said field to produce a force which accelerates each input burst through said tubular member.

7. The plasma accelerator `defined in claim 6 which further includes an exhaust chamber connected to said second end of said tubular member, and means for evacuating said exhaust chamber.

8. The plasma accelerator defined in claim 6 wherein said tubular member has a substantially cylindrical configuration.

9. The plasma accelerator defined in claim 6 wherein said tubular member has the configuration of a conical frustrum, convergent toward said second end, and wherein said field windings are positioned to produce an accelerating magnetic field which is also radially convergent whereby each of said input annular plasma bursts is accelerated radially inward as it moves through said tubular member.

l0. A plasma accelerator for producing output bursts 18 of gas plasma at terminal velocities approaching the speed of light, said accelerator comprising: a tubular accelerating structure having an input end and an output end and including a plurality of field windings stacked along the length thereof for producing a solenoidal field therethrough; means for energizing said field windings in sequence from said input end to said output end to produce a magnetic field phase -front which accelerates through said tubular structure; exhaust means coupled to said accelerating structure for maintaining a relatively low pressure therein; and means for introducing an annular gas plasma mass into said accelerating structure at said input end, said magnetic eld inducing a circulating current in said annular plasma mass which reacts with said magnetic field to produce an accelerating force which advances said plasma mass through said accelerating structure substantially in accordance with the movement of said magnetic eld phase front.

l1. The plasma accelerator defined in claim 10 wherein said last named means includes synchronizing means for synchronizing the entry of said plasma mass into said accelerating structure with the energization of said field windings.

12. A plasma accelerator for producing a gaseous discharge at relatively high velocities, said accelerator comprising: a source of an ionizable gas; an ionizing chamber coupled to said source for receiving said gas, and including means for ionizing at least a portion thereof to produce a gas plasma; a tubular linear accelerating structure having an axis, an input end and an output end, said accelerating structure including a plurality of field windings disposed along the length of said accelerating struct-ure, the plane of each field winding being normal to the axis of said accelerating structure; a source of electrical energy coupled to said accelerating structure for energizing said field windings, said field windings being positioned and energized relative to each other to produce an accelerating magnetic field through said accelerating magnetic structure from said input end to said output end; and an annular nozzle for entering gas plasma from said ionizing chamber into said accelerating structure in an annular mass whose plane is parallel to the plane of said field windings, said annular mass responding to said accelerating magnetic field by accelerating through said accelerating structure after said magnetic field.

13. The plasma accelerator defined in claim l2 wherein said field windings are positioned sequentially between said input end and said output end of said accelerating structure, and wherein said source of electrical energy includes means for sequentially energizing successive field windings in accordance with a predetermined time delay schedule to produce said accelerating field.

14. The plasma accelerator defined in claim 13 wherein each of said field windings comprises a single turn conductor, and said source of electrical energy includes a plurality of switching means corresponding respectively to said plurality of field windings for applying electrical energy to their corresponding single turn conductors.

15. The plasma accelerator defined in claim 14 wherein each of said switching means includes at least one pair of spark gap electrodes, means for connecting one of said electrodes to one end of the associated single turn electrode, and means for applying an electrical pulse signal to the other of said electrodes to break down the gap between said electrodes.

16. The plasma accelerator defined in claim 14 wherein one end of each of said single turn conductors is connected to a first reference potential, and wherein each of said switching means includes first, second and third spark gap electrodes forming first and second series spark gaps, means connecting the first spark electrode to the other end of the associated field winding, a storage capacitor connected to the third spark electrode, means for charging said capacitor to a second reference potential differing from said first reference potential, and means for applying an electrical Ypulse signal to said second electrode for magnitude larger than the breakdown potential of theY other spark gap.

17. The plasma accelerator defined in claim 14 wherein each of said switching means includes a storage capacitor, means for charging said storage capacitor to a predetermined voltage, and spark gap means selectively actuable to connect said capacitor to the associated single turn conductor to discharge said capacitor therethrough, each single turn conductor and its associated capacitor functioning as a damped ringing circuit when said actuating means is actuated, and means for actuating said spark gap means.

18. The plasma accelerator defined in claim 13 wherein said accelerating structure comprises a hollow tubular member of vitreous material, and said field windings are positioned around said tubular member along the length thereof.

19. The plasma accelerator defined in claim 18 which further includes means for selectively entering plasma into said accelerating structure in synchronism with the energization of said field windings.

20, The plasma accelerator defined in claim 12 wherein said source of electrical energy comprises a' polyphase alternator, and wherein said plurality of field windings are divided into a plurality of groups corresponding to the excitation phases of said alternator, each group of field windings being excited from the corresponding output phase from said alternator.

2l. The plasma accelerator defined in claim 20 wherein the field windings in each group of field windings are distributed along the length of said accelerator structure in a manner such that the field winding density per'unit length of accelerator structure approximates an accelerating sinusoid.

22. The plasma accelerator defined in claim 2l wherein said polyphase alternator is a three phase generator and the field winding density distribution pattern associated with each of said groups of field windings is phased 120 in space with respect to the density distribution pattern associated with the other groups of field windings.

23. The plasma accelerator defined in claim 20 wherein said accelerator structure comprises an outer annularl shell member and an inner core member concentric therewith, each of said members including a plurality of longitudinally extending and circumferentially stacked ferromagnetic laminates, said laminates in both said shell member and said inner core member being slotted at spaced intervals to provide slots for receiving said field windings.

24. A plasma accelerator for producing high velocity output bursts of gas plasma wherein the relative velocities of the particles within the plasma with respect to each other are relatively low, said accelerator comprising: a straight tubular member having first and second ends; a plurality of field windings disposed around said tubular member along the length thereof; means for electrically energizing said field windings to produce a magnetic field within said tubular member moving at a continuously increasing velocity from said first end to said second end; means for maintaining the atmosphere with said tubular member below a preselected pressure; and means for introducing an annular mass of gas plasma into said first end of said tubular member, said gas plasma having a circulating current induced therein by the action of said magnetic field,.said circulating current reacting with said field to produce a force which accelerates said plasma through said tubular member.

25. A plasma accelerator for producing output bursts of gas plasma at a relatively high terminal velocity, said accelerator comprising: an accelerator structure having rst and second ends and including means for generating a radial magnetic field which accelerates through said structure from said first end to said second end; means for introducing gas plasma into said accelerating structure ati eil) said first end in an annular mass; and means for synchronizing the introduction of said annular plasma mass' into said accelerating structure with the generation of said magnetic field to induce a circulating current in said plasma mass, said annular plasma mass responding to the circulating current induced therein and to said accelerating magnetic field by accelerating through said accelerating structure toward said second end thereof.

26. In a plasma accelerator for generating a high energy output burst of gas plasma, the combination comprising: a tubular evacuated envelope having first and second ends; means for introducing an annular mass of gas4 plasma into said evacuated envelope at said first end thereof; and means for generating an accelerating magnetic field within said envelope in synchronism with the introduction of said annular plasma mass to induce a circulating current in said plasma and to exert a magnetomotive force upon said plasma for accelerating said plasma through said tubular evacuated envelope towards said second end thereof.

27. A plasma accelerator comprising: means for generating an annular mass of gas plasma; and means for generating an accelerating magnetic field aroundV said plasma to induce a circulating current in said plasmal mass, said magnetic field having a radiall component parallel to the plane of said annular plasma mass and accelerating in a direction normal to the plane or said mass whereby said current in said plasma mass and said magnetic field coact to accelerate said mass along with said magnetic field.

28. A plasma accelerator for producing output bursts of gas plasma at terminal velocities greatly in excess of sonic velocities, said accelerator comprising: tubular accelerating structure having an input end and an output end and including a plurality of field windings positioned along the length thereof for producing a solenoidal field therethrough; means for energizing said field windings in sequence from said input end to said output end to produce a magnetic field phase front which accelerates through said tubular structure; means for .maintaining the interior of said acceleratingy structure normally at a relatively low pressure; and means for introducing a gas plasma mass into said accelerating structure at said input end, said magnetic field inducing a circular current in said mass which reacts with` said magnetic field to produce an accelerating force which advances said plasma mass through said accelerating structure substantially in accordance with the movement of said magnetic field phase front.

29. A plasma accelerator for producing a gaseous discharge at velocities in excess of sonic velocities, said accelerator comprising: a/source of an ionizable gas; an ionizing chamber coupled to said source for receiving said gas, and including means for ionizing at least a portion thereof to produce a gas plasma; an accelerating structure having an input end and an output end, said accelerating structure including a plurality of field windings disposed between said input end and said output end of said accelerating structure; a source of electrical energy coupled to said accelerating structure for energizing said field windings, said field windings being positioned and energized relative to each other to produce an accelerating magnetic field through said accelerating magnetic structure from said input end to said output end; and an annular nozzle for entering gas plasma from said ionizing chamber into said accelerating structure, said mass responding to said accelerating magnetic field by accelerating through' said accelerating structure after said magnetic field.

30. The plasma accelerator defined in claim 29 wherein said field windings are positioned sequentially between said input end and said output end of said accelerating structure, and wherein said source of electrical energy includes means for sequentially energizing successive field windings in accordance with a predetermined time delay schedule to produce an accelerating field.

Y i Y 3 3l. In a plasma accelerator for generating a high energy output burst of gas plasma, the combination comprising: an evacuated envelope having an input end and an output end; means for providing a mass of gas plasma in said envelope at said input end; and means for generating an accelerating magnetic eld within said envelope to induce a circulating current in said plasma and to exert a magnetomotive force upon said plasma for accelerating said plasma through said envelope toward said output thereof.

32. A plasma accelerator comprising: means for generating a mass of gas plasma; and means for generating an accelerating magnetic field around said plasma to induce a circulating current in said plasma mass in such a manner that said plasma mass and said magnetic field coact to accelerate said mass along with said magnetic eld.

33. A plasma accelerator comprising: means for generating a mass of gas plasma; and means for generating an accelerating magnetic field around said plasma to induce a circulating current in said plasma mass, said plasma mass being responsive to said circulating current therein for taking an annular form, said magnetic field having -a radial component parallel to the plane of said annular plasma mass which accelerates in a direction normal to the plane of said mass whereby said current in said plasma mass and said magnetic field coact to accelerate said mass along with said magnetic field.

34. A plasma acceleration for producing a gaseous discharge at high velocities and ow rates, said accelerator comprising: a source of an ionizable gas; an ionizing chamber coupled to said source for receiving said gas for ionizing at least a portion thereof to produce a gas plasma; a tubular linear accelerating structure, said accelerating structure including a plurality of field windings disposed along the length thereof; a source of electrical energy coupled to said accelerating structure for energizing said field windings, said field windings being positioned and energized relative to each other to produce an accelerating magnetic field therethrough; and means for introducing gas plasma into said accelerating structure, said gas plasma mass responding to said accelerating magnetic field by assuming an annular configuration and accelerating through said accelerating structure after said magnetic eld.

35. A plasma accelerator for producing output bursts of gas plasma at velocities greatly in excess of sonic velocities, said -accelerator comprising: an accelerating structure having an input and an output and including a plurality of field windings positioned between said input and said output for producing a magnetic field therebetween; means energizing said field windings in sequence from said input to said output to produce a magnetic iield phase front which accelerates through said structure from said input to said output; and means for positioning a gas plasma mass in said accelerating structure at said input, said magnetic eld inducing a circular current in said mass Which reacts with said magnetic field to produce an accelerating force which advances said plasma mass through said accelerating structure substantially in accordance with the movement of said magnetic eld phase front.

References Cited in the file of this patent UNITED STATES PATENTS 2,770,755 Good Nov. 13, 1956 2,798,181 Foster July 2, 1957 2,818,507 Britten Dec. 31, 1957 2,820,142 Kelliher Jan. 14, 1958 2,826,708 Foster Mar. 11, 1958 UNITED STATES PATENT oEEICE CERTIFICATE 0F CORRECTION Siegfried Hans-en error appears in J,the above numbered pat- It is hereby certified that v the said Lettere I-"aterroshould read as ent requiring correction and that 'corrected below.

Column 3,` line 26,` for nembodiments" read embodiments line 27Y for "inventon" read invention column 2L, line 29 for "acceleration" read ='aecelerator Signed and sealed this 28th day of November 1961.

' {SEAL} Attest:

ERNEST W. SWIDEE DAVID L. LADD Commissioner of Patents Attesting Officer f USCOM MDC- UNITED STATES PATENT OFFICE CERTIFICATE 0E CORRECTION Patent No. 2,992,345 July 11,y 1961 Siegfried Hansen or appears inthe above numbered pat- It is hereby certified that err Y e said Letters! Patentl should read as ent requiring correction and that th corrected below.

Column 3, linev 26, for "embodments" read embodiments line 27, for "inventon" read invention column 21, line read L-'accelerator a 29, for acceleration Signed and sealedV this 28th day of November 1961.

Attest:

ERNEST W. SWIDEE DAVID L. LADD Commissioner of Patents Attesting Officer USCOM M'DGv

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