US3110843A

US3110843A - Helical path plasma

Info

Publication number: US3110843A
Application number: US32252A
Authority: US
Inventors: Coleman Du P Donaldson
Original assignee: Thompson Ramo Wooldridge Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1960-05-27
Filing date: 1960-05-27
Publication date: 1963-11-12
Anticipated expiration: 1980-11-12

Description

Nov. 12, 1963 "3,110,843

0. DU P. DONALDSON HELICAL PATH PLASMA Filed May 27, 1960 v ewer? SUPPLY Plasma Ouf /22 INVENTOR C'o/em an du Dana/dam;

BY M w z V ATTORNEY United States Patent 3,110,843 HELICAL PATH PLASMA Coleman dn 1?. Donaldson, Princeton, NJL, assignor to Thompson Rama Wooldridge lne, Cleveland, Ohio, a corporation of @hio lFiled May 27, 1960, Ser. No. 32,252 6 Claims. ((31. 315-111) The present invention is directed to a device and method for accelerating electrically conductive plasmas.

In recent times, there has been some study made of producing electric body forces on electrically conductive fiuids. In essence, systems of this type involve subjecting the electrically conductive fluid to the combined action of electrical magnetic fields. The electric body force involved is derived from the vector product of the current and the magnetic field strengths and is perpendicular to both of these vectors. The body force per unit volume of these vectors, normal to each other, is given by the vector equation:

F=jB

where F is the body force, j is the current density vector,

and B is the magnetic flux vector.

proved plasma accelerator which reduces skin friction and heat transfer effects.

Another object of the invention is to provide a plasma accelerator which is extremely compact.

Still another object of the invention is to provide an improved method for accelerating a plasma in a controllable manner.

The acceleration parameter for the devices of the present invention is expressed as follows:

Where a is the acceleration parameter,

a is the electrical conductivity of the accelerated fiuid, m is the mass flow per unit area,

B, is the magnetic flux density in the z direction, and

s is the distance in the direction of plasma motion.

With the devices of the present invention, relatively large acceleration parameters are obtained with relatively limited magnetic fields, due primarily to the configuration provided for the plasma accelerating path.

A further description of the present invention will be made in conjunction with the attached sheet of drawings in which:

FIGURE 1 is an exploded view, partly in cross section, illustrating schematically a type of plasma accelerator coming within the present invention; and

FIGURE 2 is a modified form of the accelerator.

As shown in the drawings:

In FIGURE 1, reference numeral 16 indicates generally a magnetically permeable core, having a helical groove 11 formed therein. The groove 11 receives a helically wound conductor 12 which closes off the outer periphery of the groove 11, and provides a helical channel 13 which :forms the acceleration space for the fluid plasma. In the form of the invention illustrated, the plasma enters the device at the uppermost end of the helical channel 13 and emerges at the lowermost end, as indicated by the legend on the drawing. Electrically See insulating spacers 14 and 16 are provided to insulate the conductor 12. from the walls of the core 10.

The apparatus of the present invention is applicable to any electrically conductive medium such as a plasma consisting of ionized gas. Generally, the fluids employed will have a conductivity on the order of 5 mho per centimeter. Since air, even at elevated temperatures has a relatively low conductivity, it is desirable to improve this conductivity by seeding the air stream prior to its acceleration with an ionizable substance such as sodium or potassium. A potassium content as little as 0.1% is eilective to increase the conductivity of the air very substantially and render it readily usable in the process and apparatus of the invention.

The core 10 is disposed between a pair of opposed magnetic pole faces 17 and 18 which'provide the axial magnetic lines of flux, identified at numeral 19 in the drawings. The pole faces 17 and '18 are energized by means of

leads

21 and 22 from a suitable power supply 23. A typical value for the magnetic fiux density employed is on the order of 1 Weber per square meter.

An electrical field is provided between the inner radial surface of the conductor 12 and the core 10 by connecting the conductor 12 by means of a conductor 24 to the power supply 23, and connecting the core 10* to the power supply 23 by means of a conductor 26. Since the conductor 1-2 is otherwise insulated from the core 10, the electrical field extends across the channel 13 in a radial direction. Hence, there are provided ahnost mutually perpendicular magnetic and electrical fields which act upon the plasma during its passage through the helical path 13. A representative value for the applied electrical field strength is on the order of 400 volts per centimeter.

In some instances, it is not practical to provide large electromagnetic poles to achieve the flux densities required. For this type of application, the structure of FIGURE 2 will be employed. That structure consists of a magnetically permeable core 31 having a helical groove 32 therein defining a channel 33 for the fluid plasma. A helical conductor 34 is received between

insulators

36 and 37 and closes oil the outer periphery of the groove 32.

In the form of the invention illustrated in FIGURE 2, the magnetic field is provided by one or more turns of a coil 38 which surrounds the periphery of the core 31. The coil 38 is energized by means of conductors 39 and 41 from a power supply 42. When energized, the coil 38 provides a magnetic field illustrated by the magnetic lines of force 43.

The electrical field perpendicular to the magnetic lines of force '43 is provided by connecting the conductor 34 and the core 31 through conductors 4-4 and 46, respectively, to the power supply 42.

With the devices illustrated, many operational advantages can be achieved. Due to the way in which the current flows into and out of the device, there is little or no net twist of the magnetic field in passing through the device. Furthermore, in the device, there is a tendency for the plasma to be pinched somewhat away from the horizontal surfaces, thus reducing skin friction and heat transfer efiects.

Furthermore, the devices of the invention make it possible to tailor the strength of the magnetic field in the axial direction, as well as by controlling in the axial direction, the driving radial electric field, thereby making it possible to optimize the acceleration of the plasma. In addition, the devices, particularly that illustrated in FIGURE 2 are very compact. i

It should be evident that various modifications can be made to the described embodiments without departing from the scope of the present invention.

I claim as my invention:

1. A plasma accelerator comprising means for proas viding a helical path for the plasma, means for establishing a magnetic field axially of said helical path, and means for establishing an electrical field at approximately a right angle to said magnetic field.

2. A plasma accelerator comprisin a magnetically permeable core, said core having a helical groove therein, means for introducing an electrically conductive fluid plasma into one end of said helical groove, means for withdrawing accelerated plasma from the other end of said helical groove, means for creating a magnetic field axially of said core, and means for establishing an electrical field at right angles to said magnetic held.

3. A plasma accelerator comprising a magnetically permeable core, said core having a helical groove therein, means for introducing an electrically conductive fiuid plasma into one end of said helical groove, means for Withdrawing accelerated plasma from the other end of said helical groove, an electrical conductor disposed in said groove in spaced relation to the base of said groove, means insulating said conductor from said core, and means for creating a magnetic field axially of said core.

4. A plasma accelerator comprising a magnetically permeable core, said core having a helical groove therein, means for introducing an electrically conductive fluid plasma into one end of said helical groove, means for withdrawing accelerated plasma from the other end of said helical groove, a pair of electromagnetic pole faces abutting the opposed ends of said core to provide a magnetic field axially of said core, and means for establishl ing an electrical field at right angles to said magnetic field.

5. A plasma accelerator comprising a magnetically permeable core, means providing a helical channel along the periphery of said core, means for introducing an electrically conductive plasma into one end of said channel, means for Withdrawing the accelerated plasma at the other end of said channel, a coil surrounding the periphery of said core, means for energizin said coil to provide a magnetic field axially of said core, and means for establishing an electrical field through said core at right angles to said magnetic field.

6. A plasma accelerator comprising a magnetically permeable core, means providing a helical channel along the periphery of said core, means for introducing an electrically conductive plasma into one end of said channel, means for Withdrawing the accelerated plasma at the other end of said channel, a coil surrounding the periphery of said core, means for energizing said coil to provide a magnetic field axially of said core, a conductor received in said channel in electrically insulated relation from said core, and means for applying an electrical field between said conductor and said core.

References Cited in the file of this patent UNITED STATES PATENTS

Claims

1. A PLASMA ACCELERATOR COMPRISING MEANS FOR PROVIDING A HELICAL PATH FOR THE PLASMA, MEANS FOR ESTABLISHING A MAGNETIC FIELD AXIALLY OF SAID HELICAL PATH, AND MEANS FOR ESTABLISHING AN ELECTRICAL FIELD AT APPROXIMATELY A RIGHT ANGLE TO SAID MAGNETIC FIELD.