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FIELD OF THE INVENTION
The present invention relates to a method and apparatus for producing
microwave radiation and more particularly to such a method and apparatus
for producing high-power, pulsed, microwave radiation within apparatus
such as a pulsed microwave source including a suitable enclosure having a
static magnetic field and a source of neutral gas to be ionized.
BACKGROUND OF THE INVENTION
Great amounts of effort have been expended in the prior art in connection
with magnetic confinement of plasma for example in controlled
thermonuclear fusion devices and the like. In this connection, the plasma
comprises a highly ionized gas composed of a nearly equal number of
positive and negative free charges (or positive ions and electrons).
Because of the mutually coupled nature of electromagnetic fields within
such a plasma and the motion of the plasma charges themselves, it has been
well documented that the plasma can support unusual oscillations and wave
motions, both stable and unstable. For example, stable and unstable wave
motions in plasma are described by the McGraw-Hill Encyclopedia of Science
& Technology, particularly in Volume 10, at pages 443-461 and Volume 14 at
pages 501-507, both published by McGraw Hill Inc., 1977.
Further prior art work has been carried out in these areas having a closer
relation to the method and apparatus of the present invention. A number of
these prior art references are briefly described below.
1. Initially, work in connection with high-beta, hot-electron plasmas
produced by electron-cyclotron heating was disclosed in an article by R.A.
Dandl, H.O. Eason, P.H. Edmonds and A.C. England entitled "Resonance
Effects on Electrons in Mirror-Contained Plasmas", Nuclear Fusion, 11
(1971).
2. Efficient generation of hot-electron plasmas by microwave power with
multiple frequency components was discussed in an article by B.H. Quon,
R.A. Dandl, W. DiVergilio, G.E. Guest, L.L. Lao, N.H. Lazar, T.K. Samec
and R.F. Wuerker entitled "Impact of Multiple-Frequency Heating on the
Formation and Control of Diamagnetic Electron Rings in an Axisymmetric
Mirror", Phys. Fluids, 28 (5), May 1985.
3a. Work extending the results of a previous investigation of growing
electromagnetic waves in a gyrotropic electron plasma to
relativistic-electron energies was set forth in an article by R.N. Sudan
entitled "Electromagnetic Instabilities in the Non-Thermal Relativistic
Plasma", Phys. Fluids, 6, 57 (1963).
3b. Related work concerning a governing equation for whistler modes in the
Elmo Bumpy Torus is set forth in an article by P.N. Guzdar and R. Marchand
entitled "Whistler Instability in the Elmo Bumpy Torus", Phys. Fluids. 25
(4), Apr. 1982.
4. Production of a hot electron plasma in a magnetic-mirror field by
high-power microwave discharges was disclosed in an article by H. Ikegami,
H. Ikezi, M. Hosokawa, K. Takayama and F. Tanaka entitled "Microwave Burst
at Triggered Instability in a Hot Electron Plasma", Phys. Fluids, 11 (5),
May 1968.
5. The effects of a relativistic electron population on the temporal and
spatial growth rates of the whistler instability were described in an
article by N.T. Gladd entitled "The Whistler Instability at Relativistic
Energies", Phys. Fluids, 26 (4), Apr. 1983.
6. Further work in the area of unstable electromagnetic waves similar to
whistler modes was disclosed in an article entitled "Electromagnetic Ion
Cyclotron Instability Driven By Ion Energy Anisotropy In High-Beta
Plasmas", Phys. Fluids, 18, 1045 (1975).
7. Additional work concerning the ability of magnetically confined plasmas
created and heated by electromagnetic fields near the electron
gyrofrequency to support wave instability was disclosed in an article by
G.E. Guest and D.J. Sigmar entitled "Stability of Microwave-Heated
Plasmas", Nuclear Fusion, 11 (1971).
8. The theoretical rates of amplification of whistler waves propagating
through hot-electron plasmas with anisotropic pressures was discussed in
an article entitled "Amplification of Whistler waves Propagating Through
Inhomogeneous Anisotropic Mirror Confined Hot-Electron Plasmas" by G.E.
Guest and R.L. Miller in Phys. Fluids, 3690 (1988).
9. Both experimental and theoretical studies of hot-electron plasma
generation using oppositely directed co-linear steady-state streams of
energetic electrons interacting with a background plasma have been
reported in numerous articles many of Which are cited in an article
entitled "Oscillations Present in Plasma Electron Heating by an Electron
Beam" by I. Alexess, G.E. Guest, D. Montgomery, R.V. Neidigh, and D.J.
Rose in Phys. Rev. Letters, 344 (1968).
10. A theoretical analysis of the three-wave processes by which oppositely
directed co-linear steady-state streams of energetic electrons interacting
with a cold background plasma can produce electromagnetic waves suitable
for generating hot-electron plasmas is presented for example in a book
entitled Plasma Astrophysics by S.A. Kaplan and V.N. Tsytovich, published
by Pergamon Press (Oxford) 1973.
11. Recent experiments and theories of the three-wave processes by which
oppositely directed colinear steady-state streams of energetic electrons
interacting with a cold background plasma can produce electromagnetic
waves at twice the upper hybrid frequency was reviewed in an article
entitled "Experimental Observations of Non-Linearly Enhanced
2.OMEGA..sub.uh Electromagnetic Radiation Excited by Steady-State
Colliding Electron Beams" by T. Intrator, N. Hershkowitz and C. Chan. in
Phys. Fluids, 527 (1984).
Rather than repeating substantial background information provided for
example by the above references, each of the above references is
incorporated herein as though set out in its entirety.
Generally, prior art references such as those noted above have dealt with
the use of conventional sources of microwave energy to create and sustain
magnetically confined plasmas for a variety of applications, together With
an identification of the instabilities that can occur in such plasmas.
However, there has generally been found to remain a need for a method and
apparatus for generating microwave energy at high power levels
substantially greater than those contemplated in the prior art while
adapting the form of the high-power microwave energy for a number of
different application.
U.S. Pat. No. 4,733,133 issued Mar. 22, 1988 to the inventor of this
invention disclosed another method and apparatus for producing microwave
radiation. The method and apparatus of that invention included certain
features in common with the present invention, particularly in connection
with extraction of a beam of microwave pulses from the chamber and
direction toward a suitable target. Accordingly, that patent is
incorporated herein by reference in order to provide a more complete
understanding of the present invention.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a method and
apparatus for producing pulses of high-power microwave radiation within an
enclosure having a magnetic field, at least one magnetic-mirror region and
a source of neutral gas to be ionized, the method and apparatus comprising
the development of a selected gas pressure within the enclosure, the
generation of the magnetic field at a strength suitable for causing the
generation and confinement of a hot-electron plasma, the introduction of
at least two energetic electron beams arranged for interaction in a
background plasma in order to generate substantial power levels of
electromagnetic radiation at frequencies that are preferentially absorbed
by the hot-electron plasma through cyclotron resonance at the hot-electron
gyrofrequency or at a harmonic or overtone thereof heating by means of the
interacting electron beams being continued in order to form a generally
stable, high-beta, relativistic-electron plasma in the enclosure, a
controlled wave instability then being developed in the plasma for
producing a pulse of relatively intense microwave radiation at a frequency
near a local electron gyrofrequency of the plasma or at a harmonic or
overtone thereof. Preferably, the two steady-state interacting electron
beams are formed in co-linear and opposed relation for interaction in a
desired portion of the background plasma.
The method and apparatus of the present invention preferably contemplate
such a combination wherein heating of the hot-electron plasma is carried
out principally by collective interactions between one or more pairs of
preferably co-linear and oppositely directed electron beams, the electron
beams interacting With the background plasma to cause electron impact
ionization of the ambient gas, and subsequently to generate
electromagnetic radiation through a phenomenon known as a three-wave
process in which pairs of spontaneously occurring electrostatic waves
associated with the two electron beams interact to generate an
electromagnetic wave at twice their frequency. This electromagnetic wave
propagates radially outwardly through the plasma enclosure and, if the
frequency is suitably adjusted, is preferentially absorbed by the
hot-electron plasma that is magnetically confined in a static magnetic
field, whereby the density and average energy of the hot-electrons are
greatly enhanced.
The interacting electron beams referred to above provide the principal
source of energy within at least one embodiment of the present invention
and may be seen to result in situ generation of microwave energy at the
point of interaction within the plasma. By contrast, the method and
apparatus of U.S. Pat. No. 4,733,133 employed electron cyclotron heating
produced solely by an external microwave source adapted for simultaneously
producing multiple-frequency electron cyclotron heating and upper
off-resonant heating using microwave power at frequencies above the
electron gyrofrequency of the plasma for a similar purpose as the
interacting electron beams of the present invention.
That technique of heating from an external microwave source, referred to in
the above noted patent as "electron cyclotron heating" is also
contemplated for optional use in the present invention together with the
interacting electron beams as a supplemental heating source for optimizing
operating conditions of the invention. In particular, the present
invention contemplates the use of such electron cyclotron heating from an
external microwave source, but at reduced power levels, preferably for
producing multiple-frequency electron cyclotron heating in order to
optimize performance of the present invention. For example, the external
microwave power source may be employed to maintain the desired anisotropy
of the hot-electron plasma and/or the density of the background plasma
while carrying out the method of the present invention.
It is further contemplated within the method and apparatus of the present
invention that the high-power microwave radiation formed within the
enclosure be withdrawn from the enclosure through focusing means for
concentrating sequential microwave pulses into a beam of focused radiation
and directing the beam onto a remote target for concentrating energy
therein. Preferably, the method and apparatus is adapted for directing the
beam toward a target including electronic circuit means and conditioning
the beam so that it is coupled into the electronic circuit means for
developing substantial amounts of energy in the target.
In view of the preceding objects, the method and apparatus of the present
invention include obvious potential for destroying or rendering inoperable
electronic controls essential, for example, in offensive weapons systems.
Suitable target applications of this type include boost and post-boost
vehicles, collateral action on sensors and communications systems as well
as satellite-based systems. The present invention contemplates a method
and apparatus for effectively concentrating energy in such targets through
the development of high-power microwave pulses With very rapid rise times
and frequencies corresponding to characteristic operating frequencies of
the target system.
Such operating frequencies are at very high levels and are expected to be
at even higher levels in future generation devices. In prior art sources
of microwave power, the maximum emitted power decreases rapidly with
increasing frequency, principally because the size of a resonant structure
decreases with increasing frequency while the power density increases with
frequency to unacceptable levels. Thus, high-power microwave energy is now
generally available only at frequencies that are well below the
characteristic frequencies of many such systems. Under these conditions,
coupling is primarily through apertures not intended for microwave
propagation, with efficiency being consequently much less that achieved by
direct coupling.
The importance of such applications and the limitations inherent in present
microwave sources underline the urgent need for method and apparatus such
as provided by the present invention for preferably producing pulsed,
high-power microwave energy, with power levels above 10.sup.12 Watts for
example at frequencies greater than eighteen gigahertz (GHz) and more
preferably for generating short repetitive pulses of microwave power at
levels in the range of about 10.sup.10 -10.sup.14 watts with frequencies
above about 35 GHz.
Prior art microwave sources have also been found to exhibit a "resonant
structure" problem in the form of unfavorable frequency dependence of peak
power because the size of their interaction region is proportional to the
wave length emitted. Moreover, electron energy or beams used in existing
devices must generally operate at high voltages to ameliorate or overcome
the space-charge effects that degrade source performance.
The present invention circumvents conventional resonant-structure problems
and space-charged limitations by using microwave energy stored in a
magnetically-confined, electrically neutral, relativistic-electron plasma,
rather than an electron beam. The stored energy is built up over a period
of seconds, for example, by beam-plasma interactions using moderate
steady-state levels of DC power supplied in the form of one or more pairs
of interacting and preferably co-linear, oppositely directed electron
beams whose energy and current are chosen for efficient generation of
magnetic-mirror confined hot-electron plasma. In normal operation, the
stored energy is built up in a much shorter time, for example, in a
fraction of a second. This technique of employing interacting electron
beams relies upon a phenomenon referred to as the three-wave process, as
also noted above.
Because of the temporal compression brought about by the sudden
transformation of energy built up much more slowly, very high-power pulses
can be produced repetitively from much lower power, DC electron beam
sources operating at energies and current levels required or selected for
the particular application. The peak power that can be achieved increases
with frequency and with the volume of the magnetic-mirror configuration
used to confine the relativistic-electron plasma. This permits very
favorable scaling for applications of the type described above as
described in greater detail below.
The method and apparatus of the invention employ a confining magnetic field
forming an elongated, cylindrical, axisymmetric, magnetic-mirror region
that is constricted at one or more axial positions inside its plane of
reflection symmetry by additional, axisymmetric magnetic coils. Upon
initiation of an operating cycle, the magnetic field preferably has the
form of two or more co-linear magnetic mirrors, formed inside a conducting
shell that serves as a vacuum chamber and as an enclosure for microwave
power.
Gas pressure within the chamber is reduced to an appropriate level (about
10.sup.-5 Torr), the magnetic intensity is raised to a pre-selected level
(about 2 Tesla) and the three-wave processing resulting from interaction
of the two electron beams is continued for in situ generation of microwave
energy in the chamber at a power level suitable for creating a
relativistic-electron plasma with a beta value approaching unity. A
suitable power level, for example, would be a fraction of one
Watt/cm.sup.3. Beta is the ratio of plasma pressure, p, to magnetic energy
density, B.sup.2 /2.mu..sub.o, where B is the magnetic field strength and
.mu..sub.o is the magnetic permeability of free space. Beta is a
dimensionless measure of the energy density stored in the plasma.
The beam-plasma interactions of the present invention are preferably
designed to yield a stable, high-beta, hot-electron plasma in the form of
two or more separate annular rings located in the co-linear mirror
regions. The plasma is below the threshold for unstable growth of a class
of electromagnetic waves propagating along field lines. such as whistlers,
by virtue of their broad distribution of electrons in relativistic
energies and the spatial variation of magnetic intensity, together with
moderate pressure anisotropy, controlled by the heating process.
In a second phase of operation, auxiliary magnetic coils, for example, are
energized to alter the spatial shape of the magnetic field into a single
elongated magnetic mirror with a nearly uniform central region. This
alteration is accomplished in a time that is much shorter than the
hot-electron confinement time, resulting in adiabatic compression and
merger of the separate annular rings of plasma formed in the first phase.
This adiabatic compression increases both the pressure anisotropy and the
magnetic field uniformity, bringing the hot-electron plasma to the
threshold for unstable growth of the desired plasma waves.
In the method and apparatus of U.S. Pat. No. 4,733,133, a short pulse of
microwave power was then injected to initiate an unstable wave, such as a
whistler, and to create a denser cold plasma at the ends of the
hot-electron plasma. That technique for producing a whistler wave
instability in the plasma according to the above noted patent is referred
to herein as operation in an oscillator mode in order to distinguish from
a corresponding mode of operation described immediately below.
For operation in an amplifier mode according to the present invention, the
wave to be amplified is introduced at one end of the enclosure or static
magnetic field in the form of a whistler wave which propagates parallel to
the magnetic lines of force and passes through the region of space
occupied by the hot-electron plasma whereby the whistler wave can be
greatly amplified if the wave frequency lies within a suitable chosen
range. The amplified wave continues to propagate along the magnetic field
lines and can be guided therealong into a quasi-optical structure
described below for focusing the amplified wave into an outgoing beam of
microwave power.
At the end of the high-power pulse, the auxiliary magnetic coils used for
adiabatic compression are switched off and the magnetic field relaxes to
its initial form. The operating cycle is then repeated to form sequential
output pulses of microwave energy.
The present invention contemplates generation of a wave instability within
the hot-electron plasma in either the oscillator mode or amplifier mode of
operation as described above with power principally being supplied by the
pairs of oppositely directed steady-state electron beams through the
three-wave effect produced by interacting beam electrons as noted above.
However, the present invention also contemplates the employment of the
amplifier mode of operation for generating a wave instability either in
combination with the three-wave effect referred to above or by the
introduction of microwave energy into the plasma from an external
microwave source in the manner disclosed by U.S. Pat. No. 4,733,133.
There are several important features of the present invention. In the
initial phase, it is essential for efficient creation of stable,
high-beta, hot-electron plasmas to use a suitably designed beam-plasma
system for efficiently generating, by means of the three-wave process, an
adequate level of electromagnetic wave power at frequencies near the
relativistic-electron gyrofrequency or near a harmonic or overtone thereof
in the hot-electron plasma or active medium to permit subsequent
development of a whistler wave instability. As noted above, the three-wave
process is preferably carried out by one or more pairs of preferably
co-linear, oppositely directed steady-state electron beams caused to flow
along the magnetic field lines through a background plasma that is
generated by the electron beams through ionization of ambient gas.
If the density of this background plasma is maintained at a suitable level,
for example, by proper adjustment of the ambient gas pressure and possibly
through low-power electron cyclotron heating using an external source of
microwave power, then the beam-plasma interaction will lead to the
spontaneous generation of electromagnetic waves which can be
preferentially absorbed by the hot-electron plasma. This preferential
absorption takes place, for example, if the frequency of the spontaneously
generated electromagnetic waves is near the second harmonic of the
hot-electron gyrofrequency in the spatial region where the hot-electron
plasma is confined.
The use of adiabatic compression of the plasma in an equilibrium condition
to bring the plasma to the threshold for unstable growth of plasma waves
is based on the identification of pressure anisotropy and magnetic field
uniformity as the most effective control parameters for this mode. This
identification is supported by a large number of theoretical studies of
unstable electromagnetic waves (such as whistlers) as well as the closely
related Alfven Ion Cyclotron mode. Adiabatic compression increases the
perpendicular velocity of energetic electrons preferentially, thereby
increasing the perpendicular pressure relative to the parallel pressure.
The particular type of adiabatic compression used in the present invention
has the added beneficial effect of bringing most of the plasma into a
uniform magnetic field region and maximizing the fraction of the stored
energy that is transformed into microwave power.
Finally, the use of a transient cold-plasma layer to reflect the growing
whistlers in the oscillator mode of operation is analogous to Q-switching
in conventional lasers. The objective is to further maximize the
conversion of stored plasma energy to microwave power.
Additional objects and advantages of the invention will be apparent from
the following description having reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a generally schematic representation of a device comprising a
magnetic mirror region enclosure for magnetically confining a plasma in
accordance with the present invention.
FIG. 2 is a view of the same device as illustrated in FIG. 1 but in a
second operating stage described in greater detail below for introducing
an unstable wave into the confined plasma.
FIG. 3 is a generally schematic representation of a whistler launcher
suitable for use in the device of FIGS. 1 and 2.
FIG. 4 is a schematic representation of the same device while illustrating
additional components for causing a focused beam of microwave energy to be
directed toward a remote target.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As discussed above, the present invention provides a method and apparatus
for efficiently storing substantial energy densities in high-beta,
hot-electron plasmas, created and sustained by beam-plasma interactions in
a suitable magnetic mirror device. A large fraction of this energy can be
released in a short time by triggering suitable plasma instabilities such
as unstable whistler waves driven by excess pressure anisotropy. Useful
collective modes with frequencies at about the electron gyrofrequency and
linear growth rates that are a significant fraction of the electron
gyrofrequency can be stimulated either by proper design of a whistler Wave
coupler-launcher, according to the present invention or by proper design
of ECH components, and also disclosed in U.S. Pat. No. 4,733,133, and
magnetic systems within the invention. Under suitable circumstances, it is
anticipated that the method and apparatus of the invention are capable of
generating relatively short pulses of microwave power, for example, at
levels in the range from about 10.sup.10 -10.sup.14 Watts, at frequencies
above 35 GHz, and with repetitive or sequential rates greater than one per
second.
Thus, the method and apparatus of the invention are believed to have
utility in a number of applications employing high-power microwave
radiation developed in a magnetic mirror device and preferably transferred
from the device through a focusing means to produce a pulsed beam of
microwave radiation. This aspect of the invention makes possible the
generation of high-power microwave beams which can be directed at remote
target systems.
The present invention can thus provide a compact, rugged source of high
power microwave and millimeter wave radiation for numerous applications in
electronic warfare and in industrial applications of non-equilibrium
plasma chemical processing. The source is broadly tunable, provides high
power at high frequency and is readily scaled in size to provide super
power pulses. Such applications are discussed for example in "MicroWave
Heating Systems for Atmospheric Pressure Non-Equilibrium Plasmas" by G.E.
Guest and R.A. Dandl in Plasma Chemistry and Plasma Processing (1988).
This reference is also incorporated herein.
A growing number of applications for microwave and millimeter wave
radiation present requirements that cannot be satisfactorily met with
existing fundamental mode sources. These requirements include high power
at high frequency with high efficiency, longer pulse lengths, tunability,
and amplifier operation together with compact size, ruggedness and good
reliability. An illustrative example in electronic warfare is the
destruction of electronic controls, sensors, and communication systems.
The most effective approach to coupling microwave power into the target
utilizes super-power pulses with rapid rise times at the characteristic
operating frequency of the target system. These frequencies are already
high and expected to be higher in next-generation systems. Even now, high
power is available only at frequencies below the characteristic
frequencies of offensive weapons systems; and coupling must therefore be
primarily through apertures not intended for microwave propagation with
far lower efficiency than would be possible for direct coupling.
The capabilities of existing sources meeting these requirements are limited
largely because the generation of power is based on the passage of
high-energy electron beams through resonant structures. The maximum power
emitted by such devices decreases rapidly with increasing frequency,
Pf.sup.2 constant, where P is the power emitted at frequency f. This
limitation arises principally because the size of the resonant structure
is proportional to the wavelength, .lambda.=c/f; and increasing the
frequency (decreasing the wavelength) increases the power density that
must be handled by the resonant structure. The resulting power density
limitation in conventional microwave sources is further exacerbated at
high power by the need to increase the electron beam voltage to reduce
space-charge effects which would otherwise degrade the source performance.
The present invention circumvents the conventional beam transit time,
resonant structure, and space charge limitations by storing energy in a
magnetic-mirror confined, electrically neutral, hot-electron plasma and
periodically transforming a fraction of this stored energy into pulses of
very high peak power. The transformation is mediated by a whistler wave
preferably launched at one end of the mirror-confined plasma, propagating
along the magnetic lines of force, amplified by the anisotropic
hot-electron plasma, and subsequently collected and focused by
quasi-optical elements at the opposite end of the plasma. The operating
frequency of this amplifier is determined by the strength of the static
magnetic field and can therefore be scaled to very high values. The gain
is determined by the physical dimensions and the energy density of the
mirror-confined plasma so that the output power can be increased by
scaling in size. Because both the operating frequency and plasma energy
density increase with increasing magnetic field strength, the peak power
achieved in the proposed concept increases with frequency (as well as the
volume of the magnetic mirror) to give highly favorable scaling properties
for many applications. The resulting source can operate in either an
amplifier or oscillator mode, as described in greater detail herein, have
high efficiency and be implemented in a rugged, compact embodiment.
General approaches for bringing the plasma rapidly to the threshold for
whistler amplification include control of the hot-electron temperature
anisotropy and the magnetic field uniformity, and control of the
background cold-plasma density and temperature.
The mirror-confined, hot-electron plasma that comprises the active medium
responsible for amplification for oscillations of the whistler instability
results from the collective interaction of two energetic electron streams
interacting in a mirror-confined background plasma. Experimental and
theoretical studies of hot-electron plasmas created by beam-plasma
interactions confirm the presence in the plasma of many separate regions
of high field strength which are individually coherent but mutually
incoherent. Such a volume distribution of independent regions is
especially useful for stochastic heating of a minority of the plasma
electrons to create a mirror-confined hot-electron plasma. The energy
stored in this plasma can, in turn, be used either to amplify incident
whistler waves propagating along the lines of force (amplification mode)
or as the source of spontaneous oscillation of whistler wave power
(oscillation mode). In effect, energy is stored throughout the plasma
volume by the beam-plasma interaction but transformed into a coherent,
two-dimensional form by the unstable whistler wave.
Referring to the drawings and particularly to FIG. 1, a magnetic-mirror
device of the type suitable for use within the present invention is
generally indicated at 10. The device 10 includes a suitable elongated
vacuum enclosure 12 having an axis of symmetry 14. Primary magnetic-mirror
coils 16 and 18 are arranged in coaxial relation at opposite ends of the
enclosure 12. Additional magnetic-mirror coils 20 and 22 are also arranged
in coaxial relation with each other and with the primary coils 16 and 18.
The additional coils 20 and 22 are arranged adjacent the longitudinal
center of the enclosure 12 while being operable in a generally
conventional fashion for forming two identical magnetic-mirror regions 24
as indicated in FIG. 2.
The device 10 also includes a source 26 of a suitable neutral gas for
forming a plasma within the enclosure 12 and more particularly within the
magnetic-mirror regions 24. The device 10 also includes opposed sources
27A and 27B arranged in opposition to each other along the axis 14 of the
enclosure 12 for forming colinear, opposed energetic electron beams
indicated at 28A and 28B.
Several types of electron-beam forming techniques are well known in the
prior art and discussed, for example, in an article entitled "Generation
and Heating of Plasma by Beam-Plasma Interaction" by J. Jancarik, V.
Kopecky, V. Pissl, J. Pohanka, J. Preinhaelter, M. Seidl, P. Sunka and J.
Ullschmied presented at the Third Conference on Plasma Physics and
Controlled Nuclear Fusion Research, Novosibirsk, 1-7 August 1968,
International Atomic Energy Agency. That reference is incorporated herein
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