Patent Number: 045432317
Section: description

DETAILED DESCRIPTION OF THE INVENTION Central to the concept of the invention is the generation and control of two or more toroidal z-pinch plasma current channels within a common toroidal volume so as to produce an average magnetic well within the plasma utilizing an internal hyperbolic axis. The preferred embodiment described herein uses where possible techniques and apparatus that are common knowledge in the art of producing and applying hot, magnetically confined plasmas. A preferred embodiment of the invention for use as a plasma research device is illustrated in FIGS. 2 and 3, such device producing magnetic surfaces as illustrated in FIG. 1. As illustrated in FIGS. 1, 2 and 3, a plasma comprising two discrete z-pinch discharge channels 10 and 12 is created within a primary vacuum chamber formed by a wall 14 so as to form an internal hyperbolic magnetic axis 16, separatrix magnetic surfaces 18, and elliptic axes 20 and 22 with nested closed magnetic surfaces 24 and 26, respectively. A surrounding magnetic surface 28 is also illustrated in FIG. 1. Channels 10 and 12 and chamber wall 14 are symmetric with respect to the toroidal major axis 30 and midplane 32. The chamber wall 14 may be made of nonmagnetic stainless steel, such as 316 stainless steel, or of Inconel alloy, having a thickness of about 0.3 mm. The toroidal resistance of the chamber wall is greater than 5 m.OMEGA., which is sufficiently high to permit penetration of induced toroidal electric field in much less than 1 ms to ionize hydrogen or other gases injected into the chamber at a pressure of about 1 mTorr, and to drive toroidal plasma current. The inside of the wall 14 may be cleaned in situ by a combination of dc glow discharge cleaning and baking to a temperature of about 100.degree. C., or by other effective techniques, to produce an atomically clean surface with a low outgassing rate. Other materials having low electrical conductivity and compatible with high vacuum technique as practiced in fusion devices may also be used. As illustrated, the chamber is equipped with a plurality of ports 34 for various purposes, including viewing and making measurements of the plasma and evacuating the chamber to a pressure of 10.sup.-8 Torr. Standard turbomolecular or cryopump vacuum pumping systems, not illustrated, may be used for this purpose. The chamber wall 14 is shaped so as to closely approximate the desired shape of the plasma. The major radius R of the plasma device illustrated is 0.50 m from the major axis 30 to the elliptic axes 20 and 22. The chamber defined by the wall 14 is 0.40 m high by 0.19 m wide at its widest point. Midplane width of the illustrated embodiment is 0.075 m, but the exact value of this dimension may be changed as desired or required for improved plasma performance with no change in the nature of the invention. Chamber cross sectional dimensions may be scaled to larger or smaller sizes, maintaining porportions close to those given here. The major radius of the chamber may be increased or decreased independently of cross sectional dimensions, because the plasma is insensitive to toroidal aspect ratio. The characteristic boundary shape, whose purpose is to force the formation of the parallel current channels 10 and 12 and the hyperbolic magnetic axis 16, is imparted by a shaped shell 36 and distributed induction windings 38. Shaped conducting shells have been used for many years to impart particular shapes to plasmas, with the most similar prior art applications being in internal conductor multipole devices, as in Kerst and Ohkawa U.S. Pat. No. 3,194,739, and in doublet devices, as in Ohkawa U.S. Pat. No. 3,692,626. The exact shape of the shell 36 is determined by solution of the Grad-Shafranov equation for MHD equilibrium to be described in subsequent paragraphs, in order to yield a plasma with the properties sought. At the same time, the shell 36 aids in stabilizing the plasma by repelling, by the method of image currents, any plasma current that tries to move toward the wall 14. In a small plasma research device such as the one illustrated, clearance space 40 between the chamber wall 14 and the shell 36 is approximately 3 mm. The shaped shell 36 is made of highly conducting metal, such as copper or aluminum, and it is 6 mm thick in the embodiment illustrated in FIGS. 2 and 3. The shell 36 includes an electrically non-conductive break to prohibit the flow of net toroidal current in the shell, which would otherwise act as a short-circuited secondary circuit for the induction winding 38. The break should be insulated to 10 kV to withstand transient voltages. The chamber wall 14 alone is too thin to withstand atmospheric pressure without collapsing. Therefore, after the chamber has been aligned in its correct position within the shell, as for example by means of small electrically insulating spacers, clearance space 40 is filled with a liquid silicone mixture that can be cured in situ to an elastic, solid adhesive silicone rubber, bonding the two firmly together. Thus, it is shell 36, and not the thin chamber wall 14, that resists atmospheric pressure. Silicone rubbers are not available that easily withstand 100.degree. C., the maximum bulk wall temperature during baking and cleaning. The maximum wall temperature rise expected when 100 kJ of energy is deposited uniformly on the wall during a test discharge is only 20.degree. C. The primary purpose of the induction coil 38 is to induce a toroidal electric field to ionize gas within chamber 14, thereby making plasma, and to drive sufficient toroidal current through said plasma to heat it resistively to high temperature. The poloidal magnetic field created by the z-pinch current also contributes the majority of the magnetic confinement of the hot plasma through the pinch effect, and therefore such current must be sustained for the desired duration of plasma confinement. The induction coil 38 is the primary winding of a transformer of which the plasma and, to a negligible extent, the chamber wall 14 form the secondary. This aspect of the device and the basic design considerations thereof are the same in the present invention as in RFP, tokamak and other ohmically heated toroidal plasma devices. The induction coil 38 may also conveniently serve a second purpose, namely, to supplement the shell 36 in shaping the plasma. Because magnetic flux diffuses through a shell of thickness w, minor half width b and electrical conductivity .rho. in a time .tau. shell given by EQU .tau..sub.shell =.mu..sub.o .rho.wb/2 , (6) its power to control the shape of the plasma is lost after this time. For the device illustrated in FIGS. 2 and 3, .tau..sub.shell =18 ms. However, plasma shape can also be accurately controlled by means of current distributed in external conductors, so as to provide magnetic boundary conditions identical to those of the shell. These conditions include also the so-called vertical field, which counteracts the tendency of the toroidal plasma to expand in major radius. Shaping by external coils has been demonstrated in both the Doublet II-A and Doublet III experiments. In FIG. 2, the individual turns of induction coil 38 are shown with a distribution that achieves the desired purpose. An infinitude of such distributions may be found, but the most efficient shaping is obtained when the windings are located close to the shaped shell 36, as illustrated. Satisfactory designs may also be obtained with a different number of turns than illustrated. Thus, the transition from plasma shaping by image currents in the shell 36 to shaping by the magnetic field produced by the special distribution of induction coil current conductors 38 is made smoothly, and the duration of the plasma is not limited by .tau..sub.shell. The induction coil 38 is energized in a conventional manner. For example, if the coil is split into upper and lower halves connected in parallel, a capacitor bank charged to 20 kV wll induce an electric field of 225 V/m in the toroidal direction. Such an electric field has been found to be more than adequate to establish hot plasmas in RFP experiments of similar size. Shaping coils 42 through 56 are optionally included in the invention to provide a more flexible degree of control over the shape and position of the plasma. The principle is again similar to that used to shape plasmas in Doublet IIA and Doublet III experiments. Each trim coil is energized independently of the other windings, for example, by means of a thyristor chopper power supply. Coils 42 and 44 can vary the horizontal position of the hyperbolic axis 16. Coils 46 and 48, together with coils 42 and 44, can vary the vertical positions of the plasma current channels 10 and 12, respectively, in order to optimize the average magnetic well effect. Coil pairs 50 and 52, plus 54 and 56, control the radial positions of the plasma current channels 10 and 12, respectively, in the event that plasma expansion is not exactly counterbalanced during long lasting discharges by vertical field from the induction coil 38. The trim coils can be made to perform their functions in negative feedback loops by the addition of magnetic field pickups around the periphery of the plasma to sense its state and react through suitable amplifiers to control the thyristor choppers or other power supplies. A plurality of toroidal field coils 58 are disposed about the plasma, chamber wall 14, shell 36, induction coils 38 and shaping coils 42 through 56, in order to produce the toroidal magnetic field required for stable pinch operation. The maximum toroidal field intensity to be supplied is about the same as for RFP plasmas, or less than 3/4 of the poloidal magnetic field arising at the plasma surface 28 from plasma currents providing the pinch effect. If the embodiment illustrated in FIGS. 2 and 3 carries 300 kA of toroidal plasma current, then the toroidal field coils need supply only the modest field strength of 0.45 T or less. Thus, almost any conventional toroidal field coil design may be used. The preferred design facilitates disassembly for easy access to the induction coil, shell and chamber. The design illustrated employs copper conductors of rectangular cross section, 0.02 m by 0.04 m, formed into U-shaped pieces 60 and 62, and joined with bolted joints into a 60-turn coil uniformly encircling the toroidal components. Sixty turns is a sufficient number so that ripple in the toroidal field strength from the discreteness of the coil conductors is not a problem. The toroidal field coils 58 are aligned by cylinder 66 and rings 68 through 71, 72 and 74, which are electrically insulating and may be of fiber glass or other reinforced plastic composite. Vertical beams 76 and the cylinder 66, together with radial beams 78 and 80, clamp the toroidal field coils firmly in place. The cylinder 66 also reacts the radial compressive force exerted by the toroidal magnetic field on coils 58, while the rings 72 and 74 reinforce the toroidal field coils 58 against bending outward in the direction of the major radius. The rings 68 through 71 position and support the coils 58 in the vertical direction. The rings 68 through 71 are in turn supported by the radial beams 78 and 80 which are also preferably made of plastic composite. Stiffness against overturning moments in the toroidal field coils 58, which arise from the cross force between the vertical magnetic field component from the induction coil 38 and current in the toroidal field coils, is provided by the cylinder 66 and the diagonal arrangement of the radial beams 78 and 80, as seen in FIG. 3. The toroidal field coils 58 are energized by external means not shown, for example by a pulsed dc rectifier system or, in smaller research experiments, by a capacitor bank. A current of 15.6 kA through the copper conductor is sufficient to generate 0.45 T. An iron core 82, consisting of a round central core 84 and a three-piece return yoke 86, 88 and 90 of rectangular cross section, is used to improve the transformer coupling between the induction coil 38 and the plasma secondary. The radius of the central core 84 illustrated is 0.2 m. When constructed of conventional, grain-oriented silicon transformer steel, the flux swing possible in the core is greater than 0.35 Wb, whereas extrapolation of RFP experimental data predicts that only about 0.2 Wb are necessary to form a 300 kA multipole pinch plasma of this size. The remaining 0.15 Wb of flux can be used to sustain the plasma current once established until the flux is consumed by plasma resistance. The iron core 82 is supported by beams 82 on a solid platform or floor 94. The torus assembly, comprising the chamber wall 14, shell 36, induction coil 38, shaping coils 42 through 56, and toroidal field coils 58, is supported on columns 96. The central iron core 84 is concentric with the major axis 30 of the torus assembly. The general behavior of z-pinch plasmas containing at least a small toroidal magnetic field was successfully explained by J. B. Taylor, Phys. Rev. Lett. 33 (1974), p. 1139-1141. Such a plasma contains magnetic helicity K, defined by EQU K=.intg.A.multidot.B dV (7) where B is the magnetic field, A is the magnetic vector potential defined such that .gradient..times.A=B and A=0 at the conducting shell, and the integration is over the enclosed toroidal volume. According to Taylor, a plasma can lose energy, through plasma instabilities, much more rapidly than magnetic helicity, even if the plasma has finite resistivity. Therefore, a plasma sheds its excess energy rapidly while virtually conserving its initial helicity, until the minimum energy state compatible with the fixed K and the geometry of the toroidal shell is attained. This is called a relaxed state, and it is stable to both ideal and resistive MHD instabilities because no more free energy is available unless K is changed. Taylor showed that the relaxed state obeys the condition EQU .mu..sub.o j=.gradient..times.B=.mu.B (8) where j is the current density, .mu..sub.o is the magnetic permeability of vacuum and .mu. is a constant with dimensions of (length).sup.-1. Plasmas obeying Eq. (8) have no pressure gradient, because .EPSILON.p=j.times.B, and are therefore force free. The solutions to Eq. (8) are particularly simple for very large aspect ratio tori with a circular cross section. The lowest order mode is then EQU B.sub..theta. =B.sub.o J.sub.1 (.mu.r) EQU B.sub..phi. =B.sub.o J.sub.o (.mu.r) (9) where J.sub.o and J.sub.1 are the Bessel functions, r is the minor radius measured from the minor axis of the torus, and B.sub.o is the field strength on this axis. Subscripts .theta. and .phi. refer to poloidal and toroidal directions respectively. When .vertline..mu.r.vertline.&gt;2.405, the first root of J.sub.o, the toroidal field reverses. Taylor's relaxation theory describes the principal features of circular cross section RFP plasmas as observed in experiments. In particular, plasmas tend to approach the configuration described by Eq. (9), independently of their initial state and the particular method used to produce them. Real plasmas differ slightly from the ideal Taylor states because of inevitable limitations, and therefore a low level of residual instability and turbulence is still observed in all recent pinch experiments. These limitations are principally: 1. Real plasma must have finite pressure; furthermore, substantially high pressures are desired for fusion applications. PA1 2. B, and therefore J in accordance with Eq. (8), are always large in Taylor states. Near the bounding shell, real plasmas are cold and hence have high resistance, and thus they are unable to carry the large current prescribed by Taylor states in this boundary region. PA1 1. Construct a conducting metal shaping shell whose shape is identical with the outermost magnetic surface of the desired state. PA1 2. Prior to formation of the plasma, establish a toroidal magnetic field within the enclosed, evacuated toroidal volume by suitable toroidal field coil means. The strength of this field is chosen so that it provides a toroidal magnetic flux within the shell equal to the toroidal flux of the desired plasma state. PA1 3. Inject the gas that will be ionized into plasma, using any conventional means. Optionally, the gas may be preionized. PA1 4. Induce a toroidal electric field around the torus by an external induction coil. A large electric field, typically &gt;100 V/m, is needed initially to ionize the gas completely and drive the toroidal current to the level of the desired state. PA1 5. Once established, the desired state is sustained by decreasing the induced electric field to a value just adequate to maintain the toroidal current flowing through the electrical resistance of the plama, typically .ltoreq.10 V/m. Gas may be let into the chamber slowly to replenish gas absorbed by the metal walls, as is now customary in the plasma art. PA1 6. The shape of the flux surface does not change radically as the mode amplitude ratio is changed. Therefore, a single shaping shell 36 can be used to study a continuum of neighboring equilbria by magneticaly trimming the boundary conditions by means of small currents through coils 42 through 56 external to said shell. PA1 7. Because no transformer can induce an electromotive force indefinitely, the plasma discharge will eventually terminate. The duration of the discharge is increased as the possible flux change of the transformer is increased. PA1 R=radial distance from the major axis 30 PA1 z=vertical distance from the midplane 32 ##EQU7## Furthermore, ##EQU8## where jP=poloidal current density. A principal object of the present invention, stated in the context of the preceding discussion, is to surround a central plasma, which can closely approximate a Taylor equilibrium, with a magnetic well. The additional stabilizing effect of the well acts to prevent, or at least to reduce, instabilities arising from the pressure of the plasma and from the low current boundary region. Since the magnetic field near the edge of a Taylor equilibrium is mainly poloidal, the well must be constructed with a poloidal magnetic field. The simplest example is the multipole pinch configuration, examples of which are given in the following. Consider straight multipolar systems first for mathematical simplicity, where the longitudinal or s axis is analogous to the toroidal direction .phi., and r and .theta. preserve the same meanings as in toroidal geometry. The configurations are most conveniently expressed in terms of the poloidal flux function .psi., defined by EQU .psi.=.multidot.i.sub.s .multidot.(B.times.dl) (10) EQU B=-i.sub.s .times..EPSILON..psi.i.sub.s B.sub.s (11) The integration in Eq. (10) along any arbitrary, continuous trajectory, beginning on the flux surface where .psi. is defined to be zero, which may be arbitrarily chosen. Also, dl is a vector increment along such trajectory and i.sub.s is the unit vector in the s-direction. Equation (8) can be rewritten in terms of .psi. as follows: EQU .EPSILON..sup.2 .psi.+.mu..sup.2 .psi.=0 (12) EQU B.sub.s =.mu..psi. (13) The general nonsingular solution in cylindrical coordinates is given by ##EQU6## The solution consists of the sum of linearly independent modes, specified by integral poloidal mode numbers m, with amplitudes a.sub.m ; the J.sub.m are the Bessel functions of order m. The simplest multipole plasma has the two lobe or quadrupole form. Consider .psi. given by EQU .psi.=a.sub.o J.sub.o (.mu.r)+a.sub.2 J.sub.2 (.mu.r) cos 2.theta.+a.sub.4 J.sub.4 (.mu.r) cos 4.theta. (15) which yields flux surfaces like those shown in FIG. 1 when the m=2 term predominates. The m=0 term is the only term in Eq. (14) that produces axial field at the hyperbolic axis, where at r=0. Because the preferred configuration has zero axial field at the hyperbolic axis, as was explained previously, a.sub.o should be set equal to zero. The m=2 mode alone does not have closed magnetic surfaces encircling the plasma outside the separatrix surface. Adding a moderate amount of m=4 mode, for example making a.sub.4 /a.sub.2 &gt;0.7 by external shaping means, is sufficient to produce such closed surfaces in a substantial volume and yields a configuration very similar to those shown in FIG. 1. Furthermore, the separatrix surface 18 in FIG. 1, and neighboring surfaces lie in a magnetic well. Thus, multipole pinch Taylor states with magnetic well exist. Basically, the internal conductors of a conventional multipole confinement system are replaced by Taylor equilibrium toroidal z-pinch plasma current channels, and the resultant is a multipole pinch Taylor state. Higher order multipole solutions can be constructed in a similar manner. For example, hexapole pinch Taylor states with average magnetic well are obtained when a.sub.o =0, the m=3 mode predominates, and a moderate m=6 amplitude, for example a.sub.6 /a.sub.3 =0.4, is added. The hexapole magnetic well is wider than its quadrupole counterpart, but the configuration, consisting of three z-pinch current channels, is more complicated. It is clear that still higher order multipole states with average magnetic well can be readily constructed mathematically. It is also obvious that the multipole plasma states can be oriented in any sense with respect to the major axis in a toroidal system. FIGS. 4A, 4B, 4C and 4D illustrate both quadrupole and hexapole plasmas, each in their two most symmetric orientations in toroidal geometry. Intermediate orientations are possible, but they add only complexity with no apparent increased benefit. The most straightforward method to produce plasmas approximating a desired Taylor state is to: Axisymmetric toroidal plasma equilibria with finite plasma pressure and a general specified toroidal current density j.sub.100 =j.sub..phi. (.psi.) may be calculated by solving the Grad-Shafranov equation: EQU V.sup.2 .psi.=-.mu..sub.0 Rj.sub.100 (16) where The pressure and toroidal field functions p(.psi.) and f(.psi.) may be specified arbitrarily. However, not all such equilibrium solutions are stable. Taylor states obeying Eq. (8) are stable as pinches within a conducting shell. Toroidal Taylor states are obtained from Eqs. (16) through (20) when dp/d.psi.=0 and df/d.psi.=.mu., Taylor's parameter. Realistic deviations from the ideal Taylor state can be included as finite pressure and a df/d.psi. that is virtually constant in the interior plasma and becomes small or zero at the edge, thereby forcing j to do the same through Eqs. (19) and (20). The magnetic flux surfaces of FIG. 1 are drawn from a numerical solution of the Grad-Shafranov equation with zero presure, but with df/d.psi.=.mu..sub.c (1&lt;.psi..sup.n), .psi.=(.psi..sub.c -.psi.)/(.psi..sub.c -.psi..sub.b), where .psi..sub.c =central value of .psi. (at the elliptic axes), and .psi..sub.b =boundary value of .psi.. For FIG. 1 the aspect ratio A=R.sub.o /a is 5.4, .mu..sub.c =3.15/a, dp/d.psi.=0 and n=4. Here R.sub.0 is the major radius of the elliptic axes and a is the half width of the plasma at its widest point. The exponent n=4 yields Taylor-like j/B almost to field reversal, but the current is rapidly attenuated outside of reversal. Plots of q, B.sub..phi., j.sub..phi. and &lt;B.sup.2 &gt;.sup.1/2 derived from this numerical solution are given in FIGS. 5A and 5B as a function of R through the elliptic axis 20 at height z=0.102 m for R.sub.o =0.5 m and I.sub..phi. =300 kA, which are the parameters for the apparatus shown in FIGS. 2 and 3. The toroidal field is slightly reversed, which yields the RFP-like reversed q profile. In the absence of plasma pressure, the local minima in &lt;B.sup.2 &gt; seen in FIG. 5A are sufficient evidence of the average magnetic well. Thus, the desired magnetic well is still obtained in toroidal geometry and with a realistic plasma current distribution by means of the present invention, consisting of multiple Taylor z-pinch current channels generating a multipole-like magnet well. The occurrence of average magnetic well in the multipole pinch can also be explained in simplified qualitative terms. The poloidal magnetic field is zero at the hyperbolic axis 16, because there the poloidal contributions from the two plasma current loops 10 and 12 are exactly equal and opposite. Similarly, the poloidal field is small in the vicinity of such hyperbolic axis, where the contributions from the two channels almost cancel. The separation between neighboring magnetic surfaces is greatly increased in the vicinity of the hyperbolic axis, which means that this vicinity is more heavily weighted during averaging of B.sub.P along a field line. Therefore, magnetic surfaces that come closest to the hyperbolic axis have a lesser average-poloidal field than nearby surfaces that do not approach it as closely. However, the toroidal field components must also be considered. It is a consequence of axisymmetry that the toroidal field-major radius product B.phi.R remains a constant on any givent magnetic surface. This condition is stated in Eq. (18). In the most common present art toroidal magnetic confinement systems, namely the tokamak and stellarator families, the toroidal field greatly excees the poloidal, and therefore average magnetic well can only be obtained by varying the relative average major radius positions &lt;R&gt; of neighboring magnetic surfaces. In pinch devices, toroidal field strength is comparable to its poloidal counterpart, but not small enough to be negligible. Furthermore, it can have a large variation across flux surfaces. Therefore, the toroidal field should also reach a minimum value on or near the separatrix surface 18 in order to favor the formation of an average magnetic well. For this reason, in addition to reasons cited earlier, it is advantageous to operate the present invention with the ratio of toroidal plasma current and magnetic field, or the parameter .mu. of the z-pinch current channels in terms of Taylor's theory, such that toroidal field reversal takes place at or near the separatrix surface. If exact coincidence of the field reversal and hyperbolic axis is not obtained, q will still pass through zero and change sign at the magnetic surface of field reversal, but q will reach infinity on the separatrix surface. The monotonicity of q(r) is interrupted in a narrow region near the separatrix surface in such a case. However, the infinite q and non-monotonic q(r) have produced no ill effects in doublet plasma devices, an therefore exact coincidence of field reversal with the separatrix surface is apparently not necessary for successful operation of the present invention. This anomaly in q is in such a small portion of the plasma that .vertline.q.vertline. may still be considered less than 1 substantially everywhere in the plasma, as distinguished from tokamaks. The relative positions of reversal and well may be varied to obtain best plasma confinement as determined by experimental measurement. In prior art RFP confinement a conducting shell close to the plasma has been considered a necessary requirement for plasma stability. The primary role of the shell is to resist by the image current effect the long wavelength link instabilities of the plasma, which can quench the hot plasma against the chamber wall of the apparatus. However, image currents decay exponentially at a characteristic rate approximately equal to .tau..sub.shell.sup.-1. It is therefore anticipated that RFP discharges lasting longer than about .tau..sub.shell may require a complex feedback system to prevent said kink instability. However, the external multipole field, particularly that portion generated by currents in induction coil conductors near the midplane 32 and/or in the shaping coils 42 and 44, resists displacements of the plasma current channels 10 and 12 in both z and R directions. Therefore, it may prove possible to eliminate conducting shell 36 under some conditions without suffering from plasma instability, gaining thereby greater design flexibility and simpler apparatus. In this case the shaping of the plasma into the multipole pinch configuration would be entirely by means of the external coils 38 and 42 through 56 or equivalents thereof. The present invention therefore provides a method and apparatus for making magnetically confined toroidal plasmas of the reversed field pinch variety with a bounding average magnetic well. Average magnetic well is not possible in prior art RFP configurations. The present invention closely approximates an ideally stable Taylor pinch state. The location of the average magnetic well according to the present invention is such as to exert a stabilizing influence on instabilities driven by the pressure of the plasma, particularly the m =0 resistive interchange mode centered on the q=0 flux surface. The location of the average magnetic well is also favorable for the amelioration of effects arising out of the reduced plasma currents near the plasma boundary compared to the ideal stable Taylor state. Therefore, advantages of greater stability and/or greater .beta., generically termed improved plasma confinement, may be expected compared with prior art RFP devices. While the novel aspects of a magnetic confinement plasma device in accordance with the present invention have been shown in a preferred embodiment, many modifications and variations may be made therein within the scope of the invention, as in the size, shape, and current and field intensities, as well as in application of alternate methods and techniques well known in the art of plasma and fusion. For example, the induction coil 38 may be designed to operate without an iron core 82. Furthermore, the conducting shell 36 may be constructed of separated upper and lower halves electrically insulated from each other at their midplane interface, which would allow operating the pinches in the well-known prior art aided reversal mode if desired. The device may also include various well-known appurtenances of plasma and fusion devices such as power supplies, vacuum pumps, instrumentation, blankets, heat exchangers, supporting structures and control systems. The particular embodiment described is designed for experimental and research purposes. Scaled-up embodiments intended for the production of a fusion and power will likely require these and other appurtenances.