US3014857A

US3014857A - Plasma device

Info

Publication number: US3014857A
Application number: US758633A
Authority: US
Inventors: James D Gow; John M Wilcox
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-09-02
Filing date: 1958-09-02
Publication date: 1961-12-26
Anticipated expiration: 1978-12-26
Also published as: GB881786A

Description

1961 J. D. GOW ET AL 3,014,857

PLASMA DEVICE Filed Sept. 2, 1958 53 5 52 HIGH F 2 r VOLTAGE MAGNET MAGNET MAGNET POWER POWER POWER POWER SUP L SUPPLY SUPPLY SUPPLY 54 SWITCHING MEANS 22 I6 \I \l' 11 I8) I7) Ia 29 INVENTORS. JAMES D. Gow BY JOHN M. WILCOX fiM Qf/W ATTORNEY.

.plasma axis. It is another object of the present invention to provide tgd States 3,014,857 PLASMA DEVICE James D. Cow and John M. Wilcox, Berkeley, Calif., as-

signors to the United States of America as represented by the United States Atomic Energy Commission Filed Sept. 2, 1958, Ser. No. 758,633 6 Claims. (Cl. 204-1932) as the energy is often described, it is possible to produce nuclear interactions between the ions whereby copious quautities'of neutrons are emitted. Additionally, high temperature plasmas, as herein generated, serve to fully ionize neutral atoms or molecules introduced therein. Through the choice of suitable fuel material from the plasma and by maximizing various parameters later described it is further possible to raise the plasma temperature to the range required for initiating thermonuclear reactions between plasma particles.

In this invention there is employed a very-powerful heating mechanism for plasma particles, as well as an improved plasma containment geometry to the end of maximizing plasma temperature whereby nuclear interaction of plasma particles results. It is herein contemplated that by the generation of particular magnetic and electric fieldl configurations and relations there shall be produced a controlled plasma particle trajectory wherein the application of energy to plasma particles is facilitated,

the interchange of energy between plasma particles is maximized, and the containment of plasma particles within the plasma is extended into the range of therma'lization.

It is an object of the present invention to provide a device for producing a high energy plasma.

It is a further object of the present invention to provide an axial plasma containment by a ring geometry wherein magnetic field lines converge away from the means for establishing an electron sheath in a plasma for imparting energy to plasma ions in a region of crossed electric and magnetic fields.

It is a still further object of the present invention to provide, high permeability. magnetic-field termination means at plasma extremities for producing an advantageous plasma confinement.

Yet another object of the present invention is to establish plasma rotation in crossed magnetic and electric fields wherein ions orbit through an electron sheath to receive energy then imparted to other positive plasma constituents.

A further object of the present invention is to provide high permeability magnetic-field termination means at plasma ends radially outward of the plasma axis for establishing an improved axial plasma containment.

Various other objects and numerous advantages of the invention will become apparent to those skilled in the art from the following description taken together with the accompanying drawing wherein:

FIGURE 1 is a schematic representation of a preferred embodiment of the invention; and

FIGURE 2 is a representation of magnetic field configuration at plasma ends.

Considering now a single embodiment of the invention as illustrated schematically in FIGURE 1 of the drawing,

3,014,857 Patented Dec. 26, 1961 ends thereof for attachment to vacuum pumping means,

not shown, whereby the chamber may be evacuated to low pressure.

About the, chamber 11 there is provided a magnet assembly 16 including a central magnet coil -17 and mirror coils 18 axially outward therefrom as well as end plates or rings 19 extending radially outward from the liner at the ends of the mirror magnets. These end plates are formed of a material having high magnetic permeability, preferably ferromagnetic, and may connect to a shell 22 about the coils and also formed of like, material, These and plates 19 serve to concentrate and direct the magnetic flux lines as'described more fully hereinafter.

As a further part of the device, there is provided an electrode 23 axially through the chamber .11and this electrode may be formed of metal such as aluminum or may comprise a plasma electrode or electron beam serving the purpose of establishing a relatively strong radial electric field between same and the liner 12. A further function of the central electrode 23 is the introduction of neutral particles to the chamber as fuel for ionization therein and as shown this central electrode 23 is formed as a tube with a multitude of small perforations 24 therealong. A gas source 26 is connected through a valve 27 to the central tubular electrode exteriorly of the chamber 11 to supply gas thereto; however, an alternate gas feed may be accomplished by piping 28 extending through the liner 12 and communicating through valving 29 to a gas source 31.

The ends of the chamber 11 are sealed, with an end plate 32 providing mounting for the central electrode via insulating means 33 and an opposite end plate 34 providmagnet coil 17 and a second magnet power supplies 52 across the mirror coils 18 with each power supply including appropriate switching and control means for connecting and disconnecting same to the magnets, as well as varying the magnet winding current. A high voltage power supply 53 is connected between the liner 12 and central electrode 23 in circuit with stwich means 54 and this power supply includes means for varying the output voltage thereof as Well as filtering means protecting the power supply fromvoltage surges.

As regards operation of the present invention, it is herein contemplated that there shall be for-med a radial electric field between the central electrode 23 and the liner 12 and an axial magnetic field through the chamber 11 by means of the magnet assembly 16. In starting the device, the chamber 11 is evacuated through the pump-out connections 14 by suit-able vacuum pumping means, not shown, and the

magnet coils

17 and 18 are energized from the

power supplies

51 and 52. The current'to the center and mirror coils are adjusted to produce a desired magnetic field intensity within the chamber with the mirror coils producing greater fields so that the magnetic field inthe chamber increases towards the ends of the magnet assembly to form a field geometry commonly known as a mirror. field, described in greater detail below. A gas such as deuterium from the source 26 is fed into the chamber 11 via the perforations 24 in the central electrode with the vacuum pumping speed and gas flow being adjusted to provide a suitable initial chamber pressure as, for example, 0.1 micron to 1.0 micron. The switching means 54 is actuated to apply from the power supply 53 a voltage between the center electrode and liner. In practice it has been found advantageous for certain purposes to employ a direct current voltage and superimpose thereon a high frequency voltage; however, a pulsed voltage may also be produced by the high voltage power supply 53 with the limitation that the voltage polarity does not change. Commonly, the device is operated with the liner electrically grounded and the central electrode positive with respect thereto to thereby form an anode; however, opposite polarity operation is possible.

As an example of operation the following parameters are presented:

Magnet coils-total length 48 inches.

End plate, thickness of each 1 inch.

Liner, inner diameter 8 inches. Central electrode, outer diameter /8 inch.

Gas density (initial) 3 X10 neutrals. Magnetic field, axial 10 kilogauss. Applied voltage 10 kilovolts.

With the machine described above, neutron production is found to be a function of applied voltage, magnetic field, and current. Measurement of neutron production establishes that an excess of 3X10 neutrons per second are readily obtainable with a current of the order of an ampere. A substantial neutron production occurs at applied voltages down to three kilovolts with neutron yield increasing with increased current and with increased voltage, as well as with increased ratio of end magnetic field to central magnetic field at least within a limited range.

Insofar as the physics of the device are concerned, it is established that following application of voltage between the central electrode and liner there is produced a discharge which tends to be radial but which is constrained by the axial magnetic field to travel about the central electrode, i.e., to rotate. Electrons formed by the ionization of gas within the chamber tend to collect into a sheath about the anode, here the central electrode, and the electrons there rot-ate rapidly about the central electrode under the influence of crossed magnetic and electric fields to form a very powerful ionizing medium. Gas or fuel in the form of neutral molecules escape from the central electrode to thereby difiuse radially outward into this rotating electron sheath whereby the neutral atoms or molecules are ionized as by collision with electrons in the sheath. Substantially all neutrals, i.e., neutral atoms or molecules, are ionized in the electron sheath and whileelectrons resulting from this ionization process generally remain in the sheath to increase the density thereof, the positive ions resulting from the ionization process are in the main ejected from the sheath by the large electric fields there present. These ions in general traverse orbits about the chamber to ionize neutrals therein and to give up energy to other ions. There is thus produced within the chamber 11 a plasma extending generally between the central electrode and liner within the magnet assembly, and an electron sheath about the central electrode provides most of the voltage difference between the liner and central electrode. By the maintenance of this electron sheath, wherein rotating electrons are raised to very high energy, there is provided an extremely good ionizing mechanism wherein substantially 100% of neutrals are ionized.

Considering further the theoretical aspects of the invention, it is noted that a primary consideration in producing a plasma temperature of the order required for thermonuclear reactions is the addition of heat to a generated plasma. Problems arise in this respect, for electrical current heating is a function of plasma resistance,

which for high density plasmas, is quite small compared to that of the circuit used to feed current to the plasma. Conversely, in a low density plasma, wherein electronion collisions primarily determine the conductivity, the plasma resistance is so high that excessive voltages are required to deliver appreciable amounts of energy to the plasma by electrical conduction.

In this invention the aforementioned electron sheath, in addition to serving as an ionizing medium may be considered as a means for applying energy to the plasma. ions produced in the electron sheath are radially accelerated therefrom by the strong electric field present and with a suitably strong axial magnetic field these ions will orbit in the chamber through the plasma surrounding the sheath to thereby give up energy to the plasma through collisions with ions therein. The foregoing will be seen to comprise a plasma heating mechanism which is independent of the plasma resistivity.

As a further consideration of the heating mechanism outlined above, there is by the following presented a possible theoretical explanation thereof including calculations to numerical values based upon the assumption that there is an applied voltage of ten kilovolts direct current, an axial magnetic field of ten kilogauss and generally an initial neutral density (N of 3x10 molecules per centimeter prior to the application of voltage. Without a detailed knowledge of the distribution of electron energies in the electron sheath, the exact rate of ionization of molecules in the sheath is not shown. Since the ionization cross section can be approximated as being inversely proportional to electron velocity, the mean ionization time (t,) is not very sensitive to the electron velocity distribution. The product of ionization cross section (0') and velocity (v) for electron ionization of D to D is about 6X 10* cubic centimeters per second. The ionization rate for deuterium molecules in the sheath of an electron density N =10 is then given by the relation N av=10 6 10 =6 l0 ionizations/sec./mo1ecule, and from the foregoing it will be seen that the mean life of a deuterium molecule is less than 2 microseconds. In operation of the present invention it has been observed that essentially no molecules penetrate the sheath region without being ionized. A D ion formed in the sheath region is accelerated outward by the strong electric field. With reasonably low ion or gas density outside the sheath region the ion will make a normal magnetron orbit and reenter the sheath, i.e., the ion will traverse an orbit similar to the electron orbits found in a magnetron. The time (t) spent in the sheath in the initial transit, after ionization, is given by the relation where M, is the ion mass, S is the distance from the point of ionization to the outer boundary of the sheath, e is the electronic charge, and E is the electric field. Under the assumed operating conditions of the device previously identified in the example, this time is very nearly 3 X10- seconds. Thus, with a very high probability, an ion made in the sheath will leave as a D ion. This ion will then make what may be termed a normal magnetron orbit and re-enter the sheath thereupon to be reflected again from the sheath. The time spent by the orbiting ion in substantially field free space can be closely approximated by using the cyclotron orbit period which is energy independent. This orbital time is given by the relation f being cyclotron frequency, which for D2+ in a ten kilogauss magentic field is t =2.6 10- seconds. At the end of the first orbit, the D ion re-enters the sheath and requires two sheath transit times to be. slowed to zero velocity and reflected back into a new orbit. This 5 p requires a time in the sheath of the order of 6X10- seconds. The ratio of time spent in the sheath to that spent in traversing the orbit exteriorly thereof is aheath 6 X tabs 2.6 x 10- which is equal to 2.3x l? Neglecting possible interactions wi-th the plasma surrounding the center rod it may then be stated that a molecular ion created in the sheath spends about 2% of its time inside the sheath. The sheath electrons will bombard the molecular ion and it will be ionized further from D to D+ during one of the sheath reflections, provided it has not otherwise been lost from the system. Since the ionization cross section for ionization from D to D+ by electron bombardment is not known, it is only possible to write that the time for further ionization is 1 sheath 1 in N it e orbit lolgvnvsx 23X 10 The symbols t and a refer to the time and cross section for the process of D D+ in the sheath and V refers to velocity of an electron relative to that of the molecular deuterons.

Making the assumption that the quantity a V is onethird of the cross section for D D the complete ionization rate R 10 2X10 2.3 lO- =4.6 X10 or in other words the mean life of the original D prior to becoming 2. D ion, is of the order of 2X10 seconds. If a substantial plasma density exists outside of the electron sheath, ionization to D++D or to 2D+ will probably occur before the second ionization in the sheath. 'It is of interest to note, however, that for a containment time longer than 20 0 microseconds, the process outlined above will reduce the molecular ions to D+ Without other aid. It is also of interest to compare the rate for this process with the rates for such processes as charge exchange and electron ionization in the region outside the sheath.

Consideration of the foregoing is possible following certain assumptions, and for convenience it is herein assumed that the neutral density of deuterium existing in the outer region of the plasma is 3X10 molecules per cubic centimeter and further that the average'energy of the D ion emitted from the sheath is 5 kev., corresponding to one-half of the sheathvoltage drop. The charge exchange cross section O'CE is well known for this energy to be 7X 10- cm. The macroscopic chargeexchange cross section is then 2.1 1( per cm. and the mean life of a five kilovolt D ion is given by the relation:

where N is the neutral density of deuterium, V is the average energy of the D 1 ions, andv all other symbols have their normal meaning; From the foregoing and as long as there is a substantial neutral density, it will be seen that this process dominates the reionization process.

very. substantial degree of ionization being obtained.

It is also possible to estimate the rate at which energy would be delivered to the plasma in the outer region, once watts." If 0.5 XV taken as the efiective deuteron energy *5 in electron volts, the power input is seen to be approximately 1 kilowatt.

The thermalization times are also of interest in the complete consideration of the heating mechanism, and in this relationship reference is made to Equations 49 and 50 set forth in an article by Dr. Richard Post appearing in the Review of Modern Physics, 28, 338, July 1956, whereby this quantity may be calculated. Assuming a relatively well ionized plasma of 10 ev. temperature (T and a density N of 3X10 electrons per cc., the mean thermalization time (t for fast moving particles may be stated as where T is measured in kilovolts. Applying this relationship to the presently assumed conditions, t is found to be equal to 3.7 l0 seconds; however, here note that the fact that D ions are involved is ignored although the validity of this assumption is supported by the fact that at the assumed density and temperature a D ion will be ionized to a D ion very rapidly in the outer region.

Comparing the foregoing efiects it will be seen that at an ionization of the charge exchange time and thermalization time are the same order so that thermalization will be nearly as important as charge exchange.

As the density, temperature and degree of ionization rise, the thermalization will completely dominate the situation. For a plasma of density 5 X 10 electrons per cubic centimeter, at a temperature of ev., and assuming complete ionization, the thermalization time may be calculated to be equal to 8X10 seconds. Again, it is seen that in the present device essentially all of the energy of the sheath accelerated deuterons is delivered to the plasma in a time comparable with a normal containment time of a few hundred microseconds.

From the foregoing approximate calculations it will be seen that a substantial heating mechanism is provided by the present invention and furthermore that this heating mechanism is operable within reasonable containment times, so that it is thereby possible to produce in the present invention an extremely high temperature plasma which is admirably suited for the production of extremely pure ion beams, large quantities of high energy neutrons, and possibly even the production of thermonuclear reactions wherein the average particle energy is sufiicient to interact with surrounding particles with a consequent release of energy which may be in excess of the energy applied to the system.

As may be seen from the foregoing description and general theoretical considerations, there is produced in the present invention a particularly effective ionization mechanism together with a highly advantageous plasma heating mechanism. In addition to the foregoing, there is observed in operation of the present invention a substantial containment time for the plasma generated. As previously noted, the device of this invention is adapted for operation as a direct current machine; however, it may be readily operated with a pulsed, voltage and suitable ing plasma initiation there is a very large storage of ions within the device. Certain experimental data and theoretical considerations indicate that these ions are stored Within the plasma discharge at a very high energy level; however, alternative approaches to the problem give some indication that the majority of storage occurs in the' liner walls. At any rate there is produced within the plasma extremely large quantities of high'energy neutrons which can only be produced by nuclear interaction and Whether the interaction results from the attainment of true thermonuclear conditions in the plasma or whether these interactions result from the collision of overly energetic ions in the plasma, it yet remains that the device does produce copious quantities of high energy neutrons which are highly desirable for a multitude of applications known in the art.

Of further interest in the illustrated embodiment of the present invention is the axial plasma containment attained herein. As previously discussed, the magnetic field through the plasma chamber is established by a central magnet coil together with end mirror coils, with provision being made for separate energization of these coils. It is thus possible and, in fact, desirable to energize the mirror coils of the invention to produce a more intense axial magnetic field through the plasma chamber at the ends thereof than is produced by the central magnet coil to the end of establishing a conventional magnetic mirror containment envelope for limiting axial diffusion of the plasma from the region in which it is desired to confine same. In addition to the foregoing, however, there is provided by the present invention a further axial containment means and in this respect reference is made to FIGURE 2 of the drawing. As may be seen from FIGURE 2, wherein the central electrode is eliminated for the purpose of clarity of illustration, it being understood that the central electrode is still a component of the structure illustrated in FIG. 2, magnetic flux lines 61 extend generally axially through the plasma chamber 11 to the ends of the magnet assembly 16. Because of the end plates or rings 19 disposed immediately outside the mirror coils 18 there is provided a magnetic field path of very good permeability directly adjacent the outer extremities of the magnet assembly. Consequently the magnetic lines of force Within the plasma chamber are directed abruptly outward of the chamber into the end plates. By this structure the normal solenoid magnet field is modified and it Will be seen from FIGURE 2 that in the vicinity of the end lates, or rings as they may be alternatively termed, the magnetic lines of force converge radially outward and an analogy may therefore be drawn between same and conventional magnetic mirror configurations. As is well known, converging magnetic field lines tend to repel charged particles traveling generally about such lines, as indicated at 62, and in this respect reference is made to the literature for a complete treatise of the mechanism. Suffice to say here that converging lines of magnetic force exert a retarding or repelling pressure upon charged particles traveling generally along such lines and there is produced by the end plates 19 what is herein termed a ring mirror. Thus the magnetic lines of force 61 curve radially outward of the plasma chamber into the end plates or rings in the manner illustrated in FIGURE 2 and it will be seen therefrom that these lines of force do, in fact, converge and do axially confine charged particles from traveling out of the ends of the plasma chamber. A further consequence of the particular magnetic field configuration herein produced is the varied relationship be tween the electric and magnetic fields at the center of the plasma chamber and ends thereof. Thus in the central region of the plasma chamber there is produced a perpendicular relationship between the electrostatic lines of force and the magnetic lines of force; however, at the chamber ends immediately adjacent the end plates 19 the magnetic and electric fields are parallel. A complete theoretical discussion of the results of this field relationship is not at this time possible; however, it has been found by experiment that a particularly advantageous plasma trapping action results therefrom. Of additional interest in respect to the particular magnet assembly herein employed is the fact that the concentration of magnetic field lines at the ends of the assembly, as accomplished by the end plates or rings, allows the utilization of a substantially weaker magnetic field to accomplish the same magnetic field containment as is normally obtained with more conventional magnetic mirror fields. Although it is possible to utilize a variety of materials to produce the ring mirror herein disclosed, experiments show that ferromagnetic materials are particularly desirable in this respect and that full advantage of the ring configuration is only attained through the use of ferromagnetic materials for the ring.

In addition to the uses for the present invention which have been discussed above, particular attention is also invited to the utility of this invention as an injector for a magnetic mirror machine of the Pyrotron type. Certain injection and operational difficulties in magnetic mirror machines may be overcome by the present invention for there is produced in this invention a very large quantity of fully ionized gas raised to a high temperature. By the utilization of such a high temperature ionized gas as is produced by this invention, it is possible to overcome the initial problem in magnetic mirror machines of adding sufficient energy to the particles for proper entrapment and containment of same therein. It is also possible by the injection of high energy. charged particles from the present invention to materially reduce the total containment time necessary in a magnetic mirror machine for raising the average temperature of the plasma therein to that required for thermonuclear reactions. While the present invention is not primarily directed to this utility, it appears that with further development of thermonuclear devices, and in particular those employing magnetic mirror configurations, the present invention may be found to be extremely useful and possibly even necessary to the practical operation of same.

It was mentioned above that various alternatives are, of course, possible within the intended scope of the present invention. As regards certain variations, it is of interest to note that by reversing the polarity of the high potential voltage applied between the liner and central electrode, i.e., by maintaining the liner at a positive potential with respect to the central electrode, there is then generated an electron sheath immediately interior the liner. With this reversed polarity the electron sheath is closely spaced about the interior surface of the liner and consequently serves to protect the liner from undue bombardment by ions of the plasma. Also as to the possible variations in gas injection or feed to the chamber, it is to be noted that while certain advantages lie in the particular described gas feed wherein the neutrals enter through the central electrode, quite suitable operation has been demonstrated with gas fed into the chamber by means such as the piping 28, for ionization is carried out not only in the electron sheath but also in the general plasma region and electrons resulting from the ionization process naturally fall into the sheath. Particularly, advantage may lie in the direction of neutral particles into the chamber through the liner in the instance wherein this latter structural member is maintained at a positive potential with respect to the central electrode. Likewise, various advantages may be attained by the utilization of other than a rigid central electrode, i.e., by the utilization of an electron beam directed axially of the chamber and providing thereby the negative electrode of the plasma discharge.

While the present invention has been described with respect to particular structural embodiments and in the light of defined structural limitations, it will be apparent that various alternatives are possible within the proper scope of the present invention and no limitation is intended by the foregoing but rather attention is directed to the following claims for a precise definition of the true scope of the present invention.

What is claimed is:

1. A plasma generator comprising means establishing a radial electric field about an axis through an evacuated region, means supplying neutral particles to said region for ionization therein whereby a plasma is formed in said region, means establishing a magnetic field axially through said region for radially confining charged particles therein fining plasma particles therebetween.

2. A plasma device as claimed in claim 1 further defined by said turther magnet means comprising high magnetic permeability rings about said region in axially spaced relationship.

3. A plasma device comprising an electrically conducting cylinder, an evacuated chamber, a central electrode disposed axially of said chamber in said cylinder, power supply means impressing a high voltage between said cylinder and central electrode to establish a strong radial electric field in said chamber, gas supply means controlably introducing a gas to be ionized into said chamber whereby a plasma of ions and electrons is formed about said central electrode, and means establishing an axial magnetic field through said chamber of sufficient strength to deflect the traverse'of charged particles in said plasma from impingement upon said cylinder and electrode and establish a high energy, rotating electron sheath for ionization of gas and energization of ions.

4. A plasma device as claimed in claim 3 further defined by said power supply means maintaining said central electrode at a positive potential relative to said cylinder whereby said electron sheath closely surrounds said electrode, and said central electrode having openings therein and connected to said gas supply for directing gas flow directly into said sheath wherein substantially complete gas ionization is produced.

5. A plasma device comprising means establishing a radial electric field about an axis in a continuously evacuated chamber, means controllably introducing a flow of gas to be ionized into said chamber, means establishing a magnetic field axially through said chamber with a field strength sufiicient to direct ionized gas into closed orbits about said axis, and means providing intensified magnetic field regions displaced axially in said chamber for axially containing ionized gas in said chamber, said intensified magnetic field regions each having lines of force diverging radially outward from the axis of said chamber and thereafter converging radially'outward at an annulus disposed concentrically thereabout.

6. Means for producing a high energy plasma compris ing a cylindrical liner of electrically conducting material, means for evacuating the interior of said liner to establish a low pressure region therein, a central electrode disposed concentrically within said liner, power supply means impressing a high voltage between said liner and electrode, a central magnet coil concentrically disposed about the mid length region of said liner, mirror coils disposed axially outwardly from the ends of said central coil and concentrically about said liner, a pair of high permeability annular discs extending radially outward from said liner at the outer ends of said mirror coils, a high permeability cylindrical shell concentrically disposed about said coils and secured at its ends to said discs, and means connected to said coils to supply current thereto with the current supplied to said mirror coils being of greater magnitude than that supplied to said central coil.

References Cited in the file of this patent UNITED STATES PATENTS 2,489,436 Salisbury Nov. 29, 1949 2,735,019 Dewan Feb. 14, 1956 2,826,708 Foster Mar. 11, 1958 2,868,991 Josephson Jan. 13, 1959 2,892,114 Kilpatrick June 23, 1959 2,920,234 Luce Jan. 5, 1960 2,920,235 Bell et a1 Jan. 5, 1960 2,920,236 Chambers et al I an. 5, 1960 2,967,943 Gow Jan. 10, 1961 2,971,122 Sloan Feb. 7, 1961

Claims

1. A PLASMA GENERATOR COMPRISING MEANS ESTABLISHING A RADICAL ELECTRIC FIELD ABOUT AN AXIS THROUGH AN EVACUATED REGION, MEANS SUPPLYING NEUTRAL PARTICLES TO SAID REGION FOR IONIZATION THEREIN WHEREBY A PLASMA IS FORMED IN SAID REGION, MEANS ESTABLISHING A MAGNETIC FIELD AXIALLY THROUGH SAID REGION FOR RADIALLY CONFINING CHARGED PARTICLES THEREIN AND PROVIDING A ROTATING ELECTRON SHEATH ABOUT THE AXIS OF SAID REGION AND FURTHER MAGNET MEANS ESTABLISHING AXIALLY SPACED INTENSIFIED MAGNETIC FIELDS FOR AXIALLY CONFINING PLASMA PARTICLES THEREBETWEEN.