US3624443A

US3624443A - Two-plasma gun magnetic field loading method

Info

Publication number: US3624443A
Application number: US68579A
Authority: US
Inventors: Jay E Hammel
Original assignee: US Atomic Energy Commission (AEC)
Current assignee: US Atomic Energy Commission (AEC)
Priority date: 1970-08-31
Filing date: 1970-08-31
Publication date: 1971-11-30
Anticipated expiration: 1988-11-30

Abstract

A method of loading plasma into a containment device. Two plasma streams are directed into the containment geometry from opposite sides. The streams are offset from each other in the direction of the magnetic field so that their interaction causes the streams to stop within the containment geometry.

Description

United States Patent Continuation-impart of application Ser. No. 766,417, Oct. 10, 1968, now abandoned. This application Aug. 31, 1970, Ser. No. 68,579

{54] TWO-PLASMA GUN MAGNETIC FIELD LOADING [51] Int. Cl v. "05h l/02 [50] Field of Search l76/5; 313/16], 230

[56] References Cited UNITED STATES PATENTS 3,527,977 9/1970 Ruark 313/230 X Primary Examiner-Raymond F. Hossfeld AnorneyRoland A. Anderson ABSTRACT: A method of loading plasma into a containment device. Two plasma streams are directed into the containment geometry from opposite sides. The streams are offset from each other in the direction of the magnetic field so that their METHOD 4 Claims, 3 Drawing Fig interaction causes the streams to stop withm the containment eometr 52 u.s.c| 313/161, g y

5 3% 1- 1- 8 U) DISPLACEMENT a 3 -50cm m Ecf) DEPOLARIZATION CURRENT PATH DIRECTED PLASMA STREAM 2 PAIENTEDunv 311 I97! 3, 524,443

SHEET 1 OF 2 PLASMA I E I PLASMA STREAM STREAM B Q B G INVENTOR. Jay E. Hamma/ BY PAIENTEIINHV 30 l97l 3. 624,443

SHEET 20F 2 3 a: m 2 DISPLACEMENT Q 2 -50cm 1 D.

fi B E0 3 DEPOLARlZATION CURRENT PATH N E 3% 5|- m 95 02 (D 4 0.

Fig. 3

INVENTOR. Jay E Hamme/ TWO-PLASMA GUN MAGNETIC FIELD LOADING METHOD The invention described herein was made in the course of, or under, a contract with the US. ATOMIC ENERGY COM- MISSION. This application is a Continuation if Part of SN. 766.4 I 7 filed Oct. l0, 1968 and now abandoned.

This invention relates to a method of loading a plasma containment device. More specifically, the method disclosed relates to stopping plasma stream within the containment geometry.

One of the major problems in the development of a con trolled thermonuclear device is plasma confinement. Because of the extremely high temperatures and energies, the plasma nuclei move with enormous speed and travel thousands of miles before undergoing fusion. Confinement therefore becomes quite important and new innovations are necessary. The particles cannot be allowed to simply bounce back and forth between the walls of a container because energy from the nuclei would be lost to the walls and the plasma cooled. The most promising solution to the problem is magnetic confinement. Various configurations of magnetic fields may be employed. One example is the stellarator concept in which the plasma is confined in an endless tube.

In all of the magnetic confinement devices a system must be included for introducing plasma into the confinement geometry. A highly directed plasma stream projected transversely into the confinement geometry would polarize and continue right on through without some means to halt the plasma within the magnetic enclosure. The prior art proposed that two plasma streams be directed towards each other so that when they meet, the polarization fields from the opposing streams will annihilate and the plasma will be trapped in the magnetic field. However, if the streams are directly opposed, the E fields will cause the streams to deflect rather than annihilate and they will not be trapped. The E fields will create a plasma drift as the two exactly opposed streams approach and the drift is given by V drift E XBIB Physics of FLuids, Vol. 8, No. 4, Apr. 1965, pp. 713-722.

It is therefore an object of the present invention to provide a method whereby plasma may be injected into a confinement geometry and stopped. This is accomplished by directing two streams toward each other but offset in the direction of the magnetic field. This separation of the streams adds an interaction time allowing the two streams to pass" each other before the depolarization process becomes effective and the streams are thereby stopped within the field. A conductor moving through a magnetic field with the field permeating the conductor will have an electric field orthogonal to both the magnetic field and the velocity of the conductor relative to B.

The field E is caused by polarization charge in or on the surface of the conductor. It is called self polarization if the charge creates its own polarization as it moves into the B field. The charge can sometimes be placed on the conductor from an external voltage source in which case motion is imparted to the conductor. The lorentz force is the means by which the selfpolarization charge will appear in a moving conductor, e.g., the well known homopolar generator. A simple deflection in an electric field is not to be construed by page 2, lines 4-6. The E field causes a EXF plasma drift which is the deflection observed in experiment. The E field arises from the polarization charge of the two opposing plasma streams as seen schematically in H6. 2.

In the present invention, depolarization is defined as any process which takes away the polarization charge. A simple metallic conductor takes away the polarization charge in the homopolar generator. In my invention the streams have opposite polarization because the velocities are opposite in the same B field. If the streams can be made to overlap each other along B field lines, currents will flow and the two streams will depolarize each other. These depolarization currents are observed in present plasma experiments. The depolarization current cannot build up instantaneously because of the inductance of current path. The inductance is roughly proportional to the separation distance of the two streams. The time required for the depolarization current to build up will allow the streams to pass and then no simple deflection of the streams will take place. For an approximate estimate of the interaction time-in simple terms-the two streams are electrically equivalent to an LC circuit. L is the inductance of the current path and C is a geometry factor times the dielectric constant of the plasma.

Dielectric constant =1 +41rn me /B,

where n=plasma density, m=ion mass, and c=light velocity. The interaction time is then inversely proportional to B and directly proportional to the square root of the separation of the two streams.

The above and other objects and features of the invention will be made apparent to this skilled in the art from a consideration of the following detailed'description taken in conjunction with the accompanying drawings wherein:

FIG. I is a representation of a simple toroidal magnetic field of the prior art.

FIG. 2 is a diagram of the fields generated by the two plasma streams entering the magnetic confinement field as suggested by the prior art.

FIG. 3 is a top view of a schematic diagram of the invention in which two opposing plasma streams are offset from each other and shows the polarized current path and the direction of the magnetic field generated by said streams.

The method of this invention provides for the injection of two opposing streams offset from each other in a direction of the magnetic field or along the 8" lines in FIG. 3. This separation of the streams adds an interaction time allowing the two streams to pass each other before the depolarization process becomes effective. With the streams displaced, the depolarization process occurs along the magnetic field lines and the streams arenot deflected away from each other with a significant trapping of the plasma within the magnetic enclosure.

The stream separation distance must be adjusted with regard to the characteristics of the plasma stream and magnetic field. The plasma streams are offset from each other approximately 50 centimeters for a magnetic field of the order of 6 kilogauss. It has been found that an offset of a few tens of centimeters is about right for kilogauss fields. The separation of the two streams depends on the magnetic field strength of the desired confinement field and the velocity and density of the injected plasma. In other words, the separation controls the inductance of the depolarization current path and the density and B field strength control the dielectric constant of the plasma in the B field.

In order to achieve a large trapping efficiency the streams must be simultaneous (of the order of 0.1 microsecond) and of nearly equal energy density.

Various concepts of confinement geometry have been employed. For illustration purposes, the ring geometry shown in FIG. 1 is sufficient to explain the problem of stopping the plasma within the confinement geometry. It is to be understood, however, that such a simple configuration is insufiicient to adequately confine the plasma and obtain fusion. Other modifications would have to be included but are not included here because of their complexity and the fact that their inclusion would not contribute to an understanding of the present invention. The ring geometry of FIG. 1 is provided by means of a simple axial magnetic field in the form of a torus. A toroid is wound externally with current-carrying field coils providing a magnetic field enclosure in the form of a tube that closes on itself. A plasma stream injected into the tubular confinement would not stop but continue through. The prior art suggested, in order to stop the plasma, the two streams be directed toward each other from opposite sides of the enclosure so that when they meet, the polarization fields from the opposing streams will annihilate and the plasma will be trapped in the magnetic field. The difficulty with this proposition is shown in FIG. 2. The self-polarization E-fields of the stream generate an electric field in the vicinity of contact 2. The method of claim 1 wherein the plasma streams are directed into the magnetic confinement geometry simultaneously.

3. The method of claim 2 wherein the plasma streams are symmetrical.

4. The method of claim 3 wherein the plasma streams are offset from each other approximately 50 cm. for a magnetic field of the order of 6 k6.

'6 F t t t

Claims

1. A method of introducing plasma into a magnetic confinement geometry comprising directing a first plasma stream into the confinement geometry from one side of said geometry and directing an opposing second plasma stream into the geometry from the opposite side of said geometry so that the streams are offset from each other along the lines of the magnetic field.

2. The method of claim 1 wherein the plasma streams are directed into the magnetic confinement geometry simultaneously.

3. The method of claim 2 wherein the plasma streams are symmetrical.

4. The method of claim 3 wherein the plasma streams are offset from each other approximately 50 cm. for a magnetic field of the order of 6 kG.