Note: Descriptions are shown in the official language in which they were submitted.
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APPLICANT: Brent Freeze
TITLE OF INVENTION: Method and Apparatus for Compressing Plasma
to a High Energy State
BACKGROUND OF THE INVENTION
1. FIELD OF THE INVENTION
The present invention relates generally to the field of plasma physics.
More particularly, the invention concerns a method and apparatus for
compressing plasma to a high energy state.
2. DESCRIPTION OF RELATED ART INCLUDING INFORMATION
DISCLOSED UNDER 37 CFR 1.97 AND 1.98
By way of brief background, in 1942, Enrico Fermi began discussing
the idea of joining light nuclei by nuclear fusion to generate a large source
of
energy. He suggested burning deuterium, an abundant stable-isotope of
hydrogen.
Today, the two primary approaches to the problem of achieving fusion
power production have been Magnetic Confinement (MCF) and Laser
Inertial Confinement (ICF) demonstration devices, such as the International
Thermonuclear Experimental Reactor (ITER) tokamak that uses MCF or the
National Ignition Facility (NIF) that uses ICF. These plasma experiments
scale to very large sizes, measuring double-digit meters across.
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Reactors based on these approaches scale to even larger sizes because
they occupy either extreme of the density conditions necessary to fulfill the
Lawson criterion for simultaneously achieving an energetic plasma for
sufficient duration. MCF attempts to sustain a low-density 1020 m-3 plasma
for a long duration of about 2 to 4 seconds, using external magnetic fields,
but suffers from plasma instabilities. ICF attempts to hold a high-density
1028 M-3 plasma for nanoseconds. Magnetized Target Fusion (MTF)
mitigates the problems encountered at either extreme by sustaining a
medium-density 1024 M-3 plasma for only several milliseconds, while
simultaneously reducing the minimum reactor size and cost as compared to
MCF or ICF.
Los Alamos National Laboratory (LANL) began early research into
MTF, but became hampered by the impetus to scale their experiments to use
the nearby Shiva Star capacitor bank as a power source, instead of scaling by
best available theory and experiment. The Shiva Star facility is located at
Kirtland Air Force Base in Albuquerque, New Mexico. They did not
optimize their proof-of-principle design based on physics, but rather on their
power supply limitations. Another weakness in their approach was the use
of a theta pinch, instead of a more efficient antenna method to form a
Compact Torus (CT) plasma structure. Lastly, they adhere to a non-reusable
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compression method (an aluminum can crusher), for single-shot
experimentation.
A Canadian company improved upon this earlier implementation and
attempted a smaller-scale MTF approach, one with lower input energy
needs. However, this approach introduced high-atomic-number impurities
(such as lead) that quench the plasma by radiation losses before ignition
occurs. Controlling the timing of the acoustic-compression method of this
company is also problematic.
The California Institute of Technology and Lawrence Livermore
National Laboratory (LLNL) focused on injecting a compact torus (CT) into
a tokamak, to sustain the latter. Their prototype 'Compact Torus
Accelerator' experiment showed that it was possible to both translate and
compress a compact torus plasma structure by moving it relative to a tapered
wall. However, they also experienced impurity problems (iron from steel
electrodes) and did not attempt to extend their initial achievement to a
curved geometry, such as a spiral.
The University of Washington Plasma Physics Laboratory has long
advocated cleanliness requirements to avoid plasma impurities. They also
utilize newer and more efficient methods to form and accelerate compact
toroids. However, the pure research of the University is not focused on
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advanced plasma compression for MTF and the University has not attempted
to translate a CT along a curved wall made of beryllium or lithium-silicon,
which are much lower-Z materials than their walls (made of silicon dioxide).
Prior art compact toroid compression mechanisms, include, but are not
limited to the following:
a. Explosive (liner technology) - For example the Los Alamos / Shiva Star
and like projects. Such mechanisms are not reusable, require high input
energy requirements and necessitate large system size.
b. Pneumatic (gas injection) - Such mechanisms typically exhibit pressure
instabilities and are generally too slow for large plasmas.
c. Hydraulic (hydro-forming wall) - For example, the Canadian 'General
Fusion' MTF concept. Such mechanisms, which require sub-
microsecond-precision timing, require highly complex control systems.
Also, the liquid walls of such mechanisms add high-atomic-number
contaminants to the plasma that significantly increase radiation loss
rates from the plasma.
d. Mechanical (piston) - For example, the Canadian 'General Fusion'
concept. Such mechanisms, which require repetitive sub-microsecond
timing, require highly complex control systems.
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e. Electrical (relay-piston) - For example, the Canadian 'General Fusion'
concept. Such mechanisms, which require repetitive sub-microsecond
timing require highly complex control systems.
f. Magnetic (coil-current spike) - This mechanism has been tried in
connection with many research programs, from the early TRISOPS
(experiment at the University of Florida) to the University of
Washington Plasma Physics Laboratory's latest CT devices. Such
mechanisms require good timing, a large energy input, and may induce
a plasma instability.
BRIEF SUMMARY OF THE INVENTION
The thrust of the present invention is to provide a compact toroid
plasma structure compression assembly that is superior to and overcomes the
problems associated with the various mechanisms described in the preceding
paragraphs. More particularly, through analysis of the disadvantages of the
aforementioned prior approaches, it has been possible to derive a unique set
of design features that yield a novel approach with a distinct advantage. The
details of these novel design features will be described further in the
specification that follows.
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With the foregoing in mind, it is an object of the present invention to
provide a compressor assembly of novel design within which a plasma can
be efficiently compressed to a high energy state.
More particularly, it is an object of the invention to provide a
compressor assembly of the aforementioned character, which includes an
elongated spiral passageway within which a compact toroid (CT) plasma
structure can be efficiently compressed to a high-energy state by
compressing the CT using its own momentum against the wall of the spiral
passageway in a manner to induce heating by conservation of energy.
Another object of the invention is to provide a compressor assembly
of the character described in the preceding paragraph, which includes a burn
chamber that is in communication with the spiral passageway and into which
the compressed CT is introduced following its compression.
Another object of the invention is to provide a burn chamber of the
character described in the preceding paragraph, in which a magnetic sensor
is embedded in the burn chamber for measuring the magnetic field vector
versus time.
Another object of the invention is to provide a compressor assembly
of the character described in the preceding paragraph, in which the burn
chamber comprises a toroidal ring of constant cross-section, having at least
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one entrance port for receiving the compressed CT and having a multiplicity
of smaller exhaust ports.
Another object of the invention is to provide a method for
compressing a CT to a high-energy state using a compressor having an
elongated spiral passageway by injecting the CT into the spiral passageway
in a manner to avoid ricochet of the CT along the walls of the passageway.
More particularly, in accordance with the method of the invention, ricochet
is avoided by ensuring that the bulk axial kinetic energy of the CT at the
point of injection is greater than the design "target" thermal energy sought
to
be achieved at the end of compression.
Another object of the invention is to provide a method of the character
described in the preceding paragraph in which thermal conduction losses and
particle diffusion losses are avoided by embedding a large magnetic field
within the CT during formation, prior to launching the CT into the elongated
spiral passageway. A highly magnetized CT impedes both thermal
conduction losses and particle diffusion losses perpendicular to the
embedded magnetic field lines.
Another object of the invention is to provide a method of the character
described in the preceding paragraphs, in which thermal conduction losses
and particle diffusion losses are avoided by applying a plasma-impurity
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impeding coating to the walls of the elongated spiral passageway. Examples
of these coatings include low atomic number materials, such as beryllium or
lithium-silicon.
Another object of the invention is to provide a method of the character
described in the preceding paragraphs in which, following compression of
the CT to the design "target" thermal energy, the CT is introduced into a
burn chamber comprising a toroidal ring of constant cross-section having at
least one entrance port for the compressed CT and having a multiplicity of
smaller exhaust ports.
Another object of the invention is to provide a method of the character
described in which, following compression of the CT to the design "target"
thermal energy, the CT is introduced into a burn chamber and after the burn
is complete, the compressed CT is caused to dissipate into a neutral gas,
which is pumped out of the burn chamber by means of a suitable vacuum
pump.
The forgoing as well as other objectives of the invention will be
achieved by the apparatus illustrated in the attached drawings and described
in the specification which follows.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS
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Figure 1 is a generally perspective view of one form of the apparatus
of the invention for compressing plasma to a high energy state.
Figure 2 is a generally perspective exploded view of one form of the
plasma compressor of the apparatus showing the plasma structure to be
compressed in position to be introduced into the plasma compressor.
Figure 3 is a generally perspective exploded view of the plasma
compressor illustrated in Figure 2.
Figure 4 is a longitudinal, cross-sectional view of the plasma
compressor.
Figure 4A is a cross-sectional view taken along lines 4A-4A of Figure
4.
Figure 5 is a generally perspective exploded view of the burn chamber
of the plasma compressor illustrating the plasma in its compressed state.
Figure 6 is a generally perspective exploded view of an alternate form
of the plasma compressor of the apparatus showing the plasma to be
compressed in position to be introduced into the plasma compressor.
Figure 7 is a generally perspective exploded view of the plasma
compressor illustrated in Figure 6.
Figure 8 is a longitudinal, cross-sectional view of the plasma
compressor shown in Figure 6.
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Figure 9 is a generally perspective exploded view of the burn chamber
of the plasma compressor of this latest form of the invention illustrating the
plasma in its compressed state.
Figure 10 is a list of loss equations for electrons.
Figure 11 is a list of loss equations for ions.
Figure 12 is a list of loss equations for particle transfer.
DETAILED DESCRIPTION OF THE INVENTION
DEFINITIONS
As used herein, the following symbols have the following meanings:
Symbol Meaning Symbol Meaning
Bohr radius r, wall radius
a12 1/2 for single reactant, Ry Rydberg energy
otherwise 1
As plasma surface area SnKRC stopping power for KrC
potential
A, wall surface area t time step duration
magnetic flux density T tritium
speed of light Te electron temperature
deuterium T1 ion temperature
De electron particle diffusivity TP transient radial temp.
profile
eo elementary charge vd ion velocity distribution
E0 incoming ion energy for vi ion most-probable thermal
sputtering speed
E2 electron allowed energy vp reaction product ion velocity
states
EH hydrogen ground state V plasma volume
energy
Eth sputtering threshold energy Wp variable of integration for
energy
go) free-bound gaunt factor Z average ion charge in plasma
gff free-free gaunt factor Zp ion product charge
Planck constant a fine-structure constant
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hydrogen 13e thermoelectric coefficient
He helium 7 ratio of specific heats
je electron sheath current to Ar plasma effective thickness
wall
Boltzmann constant c reduced energy for
sputtering
KL total transparency factor co electric permittivity of free
space
Kn2 2nd-order Bessel function H product particles fraction
that stay
Li ion inertial length 0 variable of integration for
time
me electron mass Kew electron-wall thermal
conductivity
in; ion mass Kiw ion-wall thermal
conductivity
Mp product ion mass sputtering decrease at low
energy
neutron, or principal Ae plasma parameter for
quantum no. electrons
nli n2 respective reactant densities A; plasma parameter for ions
ne electron density sputtering decrease fit
parameter
rips neutral gas density 1-to magnetic permeability free
space
ni ion density TC geometric pi
np reactant ion particle density aes beam reaction cross-section
Na ion density * fractional am momentum transfer cross-
ionization section
NZ reactant ion density * electric conductivity
parallel
charge/mass
absolute sputtering yield <crv> integrated reaction cross-
section
Qp reaction product energy Tie ion-electron equilibration
time
radius T time that lost product
particles stay
1-0 field null radius sti radial particle profile in
time
re; ion cyclotron radius Xe electrons to products
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velocity ratio
re classical electron radius Xi
ions to products velocity
ratio
ri ion radius
magnetic flux radial profile
in time
FUSION
The process by which two light nuclei combine to form a heavier one.
The fusion process releases a tremendous amount of energy in the form of
fast moving particles. Because atomic nuclei are positively charged -- due to
the protons contained therein -- there is a repulsive electrostatic, or
Coulomb, force between them. For two nuclei to fuse, this repulsive barrier
must be overcome, which occurs when two nuclei are brought close enough
together where the short-range nuclear forces become strong enough to
overcome the Coulomb force and fuse the nuclei. The energy necessary for
the nuclei to overcome the Coulomb barrier is provided by their thermal
energies, which must be very high. For example, the fusion rate can be
appreciable if the temperature is at least of the order on 10 keV ¨
corresponding roughly to 100 million degrees Kelvin. The rate of a fusion
reaction is a function of the temperature, and it is characterized by a
quantity
called reactivity. The reactivity of a D-T reaction, for example, has a broad
peak between 30 keV and 100 keV.
FIELD-REVERSED CONFIGURATION (FRC)
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An example of a compact toroid plasma structure is a Field-Reversed
Configuration which is formed in a cylindrical coil which produces an axial
magnetic field. First, an axial bias field is applied, then the gas is pre-
ionized, which "freezes in" the bias field, and finally the axial field is
reversed. At the ends, reconnection of the bias field and the main field
occurs, producing closed poloidal magnetic field lines. A review well
known to those skilled in the art is found in "Field Reversed
Configurations," M. Tuszewski, Nuclear Fusion, Vol. 28, No. 11, (1988),
pp.2033-2092.
COMPACT TOROID
The FRC belongs to the family of compact toroids. "Compact"
implies the absence of internal material structures (e.g. magnet coils)
allowing plasma to extend to the geometric axis. "Toroid" implies a
topology of closed donut-shaped magnetic surfaces. The FRC is
differentiated from other compact toroids by the absence of an appreciable
toroidal magnetic field within the plasma.
PRIME-MOVER SUBSYSTEM
As used herein, prime-mover subsystem means a system for
converting fusion-generated ion and/or neutron thermal energy to electrical
energy. The prime-mover subsystem may comprise a heat exchanger and
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may also comprise various types of selected direct-conversion subsystems of
a character also well known by those skilled in the art.
THE APPARATUS OF THE INVENTION
Referring now to the drawings and particularly to Figure 1, one form
of the apparatus of the invention for compressing plasma to a high energy
state is there shown and generally designated by the numeral 20. This form
of the apparatus comprises a compressor 22, a vacuum pump subsystem 24
connected to the compressor by an outlet port 25 and a wall-cleaning
subsystem that is operably associated with the compressor. The wall-
cleaning subsystem here comprises heater blankets 26a, such as those readily
commercially available from BH Thermal Corporation of Columbus, Ohio
and like sources, a glow discharge cleaning (GDC) system 26b such as a
system that is readily commercially available from XEI Scientific, Inc. of
Redwood City, California and an ion gettering pump 26c of the character
readily available from commercial sources such as SAES Getters USA of
Colorado Springs, Colorado. Apparatus 20 also includes a plasma source
subsystem 28 that here comprises stator antenna coils with pre-ionization
capability, such as those commercially available from sources such as Alpha
Magnetics of Hayward, California, a gas pulse injection valve with fire
control unit 30 of the character that is available from Parker Hannifin of
Pine
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Brook, New Jersey, and a ejector coil subsystem 32 that is also available
from Alpha Magnetics. The pre-ionization process is preferably powered by
a radiofrequency generator of the character that can be obtained from T & C
Power Conversion of Rochester, New York. As will be discussed in greater
detail in the paragraphs that follow, a prime-mover subsystem, which is
generally designated in Figure 1 by the numeral 34, must be operably
associated with a compressor 22 to convert the fusion-generated ion and/or
neutron thermal energy to electrical energy. Prime-mover 34 here comprises
a heat exchanger of a character well understood by those skilled in the art.
Attached to the heat exchanger is a steam turbine, which is, in turn, attached
to an electrical generator (not separately shown in the drawings). The primer
mover subsystem can also comprise various types of selected direct-
conversion subsystems of a character also well known by those skilled in the
art.
A highly unique feature of the apparatus of the present invention is the
previously identified compressor 22, the details of construction of which are
illustrated in Figures 2 through 4 of the drawings. In the present form of the
invention, the plasma compressor 22 comprises first and second sealably
interconnected portions 36 and 38 that are constructed from a material
selected from the group consisting of aluminum, steel, copper, silicon,
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magnesium, carbon-carbon composites, nickel super alloys, tungsten, or
other refractory alloys (such as molybdenum, niobium or rhenium).
Preferably, portions 36 and 38 are formed using a conventional computer
numerically controlled (CNC) machine, or a conventional electrical
discharge machine (EDM), or by casting methods. As best seen in Figures 3
and 4 of the drawings, each of the portions 36 and 38 is provided with an
elongate spiral passageway 40 having continuous wall 40a. Each of the
spiral passageways has an inlet 40b and an outlet 40c (Figure 3). Disposed
proximate the center of the compressor 22 and in communication with the
outlet of the spiral passageway is the important burn chamber 41, the
construction and operation of which will presently be described.
Also forming a part of the compressor 22 is an inlet port component
42 and an inner ring 44 that is operably associated with the burn chamber 41.
Inlet port component 42 is in communication with the inlet of the spiral
passageway 43 (Figure 4) that is formed when portions 36 and 38 are joined
together in the manner illustrated in Figure 2 of the drawings by brazing,
welding, diffusion bonding, or mechanical assembly (with bolts and seals).
As illustrated in Figure 2, spiral passageway 43 is of progressively
decreasing diameter with the smallest diameter of the passageway being in
communication with the burn chamber 41. Both the inlet port component
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and the inner ring are also preferably formed from a material selected from
the group consisting of aluminum, steel, copper, silicon, magnesium,
carbon-carbon composites, tungsten, or other refractory alloys.
In order to avoid contamination of the plasma during the compression
process, the wall of the elongated spiral passageway 40 of the compressor
22, as well as all other internal surfaces of the compressor that are exposed
to the plasma, must be provided with a coating "C" preferably comprising
either lithium-silicon, beryllium, or diboride ceramic, all of which are
electrically conductive and low atomic-number materials (see Figures 3 and
4A). With respect to the lithium-silicon coating, it is to be noted that
because
pure lithium metal reacts with water vapor in the air, it is necessary that it
be
strictly maintained under vacuum between the point of manufacture of the
coating powder and its application to the internal walls of the compressor.
For certain applications, an electrically-conductive diboride ceramic or
similar composite coating that consists of low atomic-number elements,
which sputter slowly, could also advantageously be used to coat the internal
walls of the compressor. The various techniques for coating the interior
walls of the compressor are well known to those skilled in the art. For
beryllium coatings, these techniques are fully described in a work entitled
Beryllium Chemistry and Processing, Kenneth A. Walsh, Edgar E. Vidal, et
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al, ASM International (2009) (see particularly, Chapter 22, "Beryllium
Coating Processes", Alfred Goldberg, pp. 361-399).
Once machined and properly coated, the inlet port component 42, the
inner ring 44 and the inner walls of the compressor 22 that are exposed to
the plasma are carefully cleaned and the various components of the
compressor are joined together in the manner well understood by those
skilled in the art, such as by brazing, welding, diffusion bonding, or
mechanical assembly.
After further cleaning and leak checks, the compressor 22 is
integrated with the other subsystems of the apparatus, of the invention in the
manner depicted in Figure 1 of the drawings. These subsystems include the
previously described vacuum pump subsystem 24, the wall-cleaning
subsystem that comprises heater blankets 26a, a glow discharge cleaning
(GDC) system 26b and an ion gettering pump 26c and the plasma source
subsystem 28. After these various subsystems have been interconnected with
the compressor and the completed system has been thoroughly tested, the
prime-mover subsystem 34 is interconnected with the compressor 22 in the
manner indicated in Figure 1 of the drawings.
Prior to operating the apparatus of the invention, it is desirable to
include a variety of well-known diagnostic tools around the apparatus (not
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shown in the drawings), such as a high-speed x-ray camera for observing
shots, along with a neutron diagnostic, plus Rogowslci coils for timing the
ejection speed of the CT through the input port, as well as the speed of the
CT in the burn chamber 41.
Before considering the methods of the invention an alternate
embodiment of the compressor unit will be considered. This alternate form
of the compression unit is illustrated in Figures 6-9 of the drawings and is
generally designated by the numeral 52. This embodiment is similar in many
respects to the embodiment shown in Figures 1 through 5 and functions in a
substantially identical manner. The primary difference between this latest
embodiment of the invention and the previously described embodiment
resides in the fact that the compressor is constructed from an electrically
conductive, metallic alloy having a low atomic number, such as a beryllium
alloy. More particularly, in this latest embodiment of the invention, portions
54 and 56 of the compressor unit 52 are formed from a block of beryllium
alloy using a conventional computer numerically controlled (CNC) machine,
or a conventional electrical discharge machine (EDM), or by casting
method. As in the earlier described embodiment of the invention and as
illustrated in Figures 7 and 8 of the drawings, each of the portions 54 and 56
is provided with an elongated spiral passageway 58 having continuous wall
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58a. Each of the spiral passageways has an inlet 58b and an outlet 58c
(Figure 7).
Also forming a part of the compressor 52 is an inlet port component
60, outlet port component 61 and an inner ring 62, the functions of which are
substantially identical to the functions of inlet port 42 and the inner ring
44
of the previously described embodiment. Both the inlet port component and
the inner ring are also preferably formed from a low atomic number,
electrically conductive material, such as a beryllium alloy. Once machined,
the inlet port component 60, the inner ring 62 and portions 54 and 56 are
carefully cleaned and connected together in the manner well understood by
those skilled in the art, such as by brazing, welding, diffusion bonding, or
mechanical assembly using bolts and seals. After portions 54 and 56 are
fused together the elongated spiral passageways 58 formed in each of the
portions cooperate to define a spiral passageway 63 (Figure 8). As illustrated
in Figure 8, spiral passageway 58 is of progressively decreasing diameter
with the smallest diameter of the passageway being in communication with
the burn chamber 65. Disposed proximate the center of the compressor 52
and in communication with the outlet of the spiral passageway 63 is the
important burn chamber 65 of this latest form of the invention, the
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construction and operation of which is substantially identical to the
previously identified burn chamber 41.
Other candidate materials for use in constructing the compression
structure 52 include Carbon-Carbon composites and refractory metal alloys
(both higher atomic number materials than Beryllium).
The use of the beryllium alloy material in constructing the compressor
is somewhat less desirable than the use of the more common materials such
as steel, copper, silicon, magnesium, tungsten or other refractory alloys, all
of which absorb x-rays better than beryllium. Additionally, the use of these
materials is considerably less hazardous and the materials combine the
function of a vacuum structural wall and x-ray shielding wall into one
component.
It is to be understood that a variety of gasses, including but not limited
to: hydrogen, deuterium, deuterium-tritium mixtures, pure tritium, helium-3,
diborane and mixtures thereof can be used with the compression apparatus
of the invention. In the case that the compression apparatus is used to
compress a deuterium-rich gas to ignition and/or "burn" conditions, a
portion of the burn ash will contain the rare gas helium-3. This is because
the helium-3 generated from the reacted deuterium has a slower initial speed
than other generated particles, such as tritium, and thus more easily
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thermalizes in the plasma. However, its nuclear fusion reaction rate is also
slower than the tritium-deuterium reaction rate, such that it is not consumed
as fast as the thermalized tritium. As a result of this breeding process, the
ash from deuterium reactions accumulates the rare stable isotope helium-3.
In order to collect the helium-3, a filtration system attached to the
vacuum pumps will need to separate the isotopes in the exhaust. This
apparatus is used to collect and purify the helium-3, as well as other exhaust
products (such as tritium) that should not be vented to atmosphere from the
pump exhaust. Additionally, hydrogen-1 (protons) and helium-4 could be
obtained from the exhaust using an isotopic separating filtration system.
The first step in carrying out the method of the present invention is to
form a compact torus (CT) plasma structure. One type of CT is the Field
Reversed Configuration (FRC). An FRC is formed in a cylindrical coil
which produces an axial magnetic field. First, an axial bias field is applied,
then the gas is pre-ionized, which "freezes in" the bias field, and finally
the
axial field is reversed. At the ends, reconnection of the bias field and the
main field occurs, producing closed field lines.
Following the formation of the CT, unlike the previously identified
prior art methods which involve the use of compact toroid compression
mechanisms, the CT, which is identified in the drawings by the numeral 68,
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is launched at high speed into the inlet port component 42 of the plasma
compressor of the invention. As will be discussed in greater detail in the
paragraphs that follow, as the CT travels through the plasma compressor it is
crushed against a low atomic number material wall of the elongated spiral by
means of its own inertia, inducing heating by conservation of energy. The
internal thermal energy of the CT increases as its kinetic energy decreases.
As the CT compresses against the walls of the spiral passageway 43,
the pressure force it exerts has a vector component in the opposite direction
to its forward motion (unless the walls are of constant cross-section).
Therefore, it is important that the bulk axial kinetic energy of the CT at the
point of ejection be greater than the design "target" thermal energy at the
end of compression, to avoid a ricochet effect along the walls.
The wall of the spiral passageway 43, as well as the other walls of the
plasma compressor into which the CT comes in contact, absorb a portion of
the heat, the degree to which is significantly reduced by embedding a large
magnetic field within the CT during formation, prior to ejection. A highly
magnetized CT impedes both thermal conduction losses and particle
diffusion losses from its core to the walls.
Once compressed to the design "target" thermal energy, the
compressed CT 68a enters a comparatively short transfer conduit 70, which
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guides it away from the plane of symmetry of the compressor, and into the
burn chamber 41. As previously discussed, the burn chamber comprises a
toroidal ring of constant cross-section, with a single entrance port for the
compressed CT 68a (Figures 3 and 7), and multiple smaller exhaust ports 72
(Figure 5) which are in communication with the vacuum system 24.
After the burn is complete, the compressed CT 68a dissipates into
neutral gas, which is pumped out through the main vacuum exit port 74.
Referring to Figures 5 and 9 of the drawings, it is to be noted that the inner
ring is provided with a circular hole 78, which is adapted to receive an
alignment gauge pin during assembly (not shown). After assembly, the
alignment gauge pin is removed, leaving two through-holes that can be
conveniently used for the insertion of diagnostic probes, such as a Rogowski
coil loop.
A major advantage of the method of the present invention is that
neutral beams are not necessary for heating the plasma, maintaining the
compact toroid plasma thermal energy, or providing stability to the plasma
structure. Another advantage of the method is that collapsible walls are not
needed for compressing the plasma. Additionally, in practice, the
compression apparatus of the invention can be used multiple times.
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By way of background, in burning deuterium, which is an abundant
stable-isotope of hydrogen, the reaction cycle consists of the following five
equations:
Primary neutron-branch 2D+2
D-3 He(0.8 MeV)-1-n(2.4 MeV)
Primary proton-branch 2 D+2.--, il_>3
T(1.0 MeV)+1 H(3 .0 MeV)
Secondary helion-branch 2D+3 He¨>4 He(3 .7 MeV)-F1H(1 4.7 MeV)
Secondary triton-branch 2 D+3,-.-,_>4
lle(3.5 MeV)+ n(14.0 MeV)
Tertiary triton-branch 3 T+3
T¨>4 He(3.8 MeV)+,, n(3.8 MeV)+(; n(3.8 MeV)
It is important to understand that in carrying out the method of the
present invention, the wall of the spiral passageway, as well as any surface
that the CT plasma structure comes in direct line-of-sight contact with, be
clean, of low atomic number, and sputter slowly. These features will
minimize losses due to impurities entering the plasma from the walls. In
addition, it is beneficial for the walls to be electrically conductive, as
this
minimizes the loss due to synchrotron (cyclotron) radiation from the heated
plasma by reflecting the emitted millimeter-wavelength light back into the
plasma for re-absorption. This becomes apparent upon reviewing the
fundamental equations governing the energy balance for the system.
The equation for the power gained by fusion reactions is:
Fusion Gain Pf = a12n1n2(av) A.1
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The loss equations for electrons, ions, and particle transfer appear
respectively in Figures 10, 11 and 12 of the drawings with all variables
being as defined in the previously set forth symbol definition table.
A key observation, based on these equations, as well as prior
experiment literature, is that avoiding impurity-driven losses is a crucial
requirement for maintaining a hot plasma. To accomplish this, it is essential
that the plasma not come into contact with high atomic number (high Z)
materials, such as steel. The end-result of impurities in the plasma is that
the
loss rates increase by orders of magnitude. There are multiple loss paths due
to high-Z contamination. The volumetric radiation power loss mechanisms
that increase most significantly with Z are Bremsstrahlung, Recombination,
and Excitation Line. However, the average Z also influences thermal
conduction losses and even thermalization rates.
Bremsstrahlung radiation is strongly affected by the average ion
charge Z of the plasma, as the multi-pole non-relativistic equation A.2
(Figure 10) indicates. In addition to this equation, it is important to
calculate
both the dipole and relativistic versions of the Bremsstrahlung loss rate, as
well as all the quantum-mechanical "gaunt factor" corrections for each ion
species, before arriving at the dominant loss rate due to Bremsstrahlung
radiation. Bremsstrahlung occurs in the x-ray spectrum and leaves the
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plasma. However, Bremsstrahlung is dominant only at high energy levels
that are commensurate with burn conditions. For this reason, and the fact
that the plasma is transparent to x-rays, Bremsstrahlung is usually the
primary loss mechanism considered in simulation programs. At lower
energy levels, which the plasma must pass through in order to get from a
neutral-gas state to burn conditions, recombination and excitation line
radiation dominate the plasma's radiative loss mechanisms. This is
especially the case for high-impurity content plasma.
Recombination radiation, governed by equation A.3 (Figure 10), is the
loss most strongly affected by Z. As can be seen inside the integrand,
recombination radiation is extremely sensitive to increases in Z. It can be
orders of magnitude less than Bremsstrahlung for a pure hydrogenic plasma,
but can rapidly exceed Bremsstrahlung at lower energy levels from even
moderate impurity content. Thus, by controlling impurities, the
recombination radiation loss mechanism can be minimized. Similarly,
excitation line radiation in equation A.4 (Figure 10) is affected by Z.
Although not as apparent from this top-level equation, the calculation of Na
utilizes a nonlinear function with Z as a directly dependant variable.
Recombination and line radiation are often over-looked in sizing
calculations, as they are assumed to be negligible as compared to
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Bremsstrahlung. This is the case under certain circumstances, but it is
important to include their equations in case impurities enter the plasma.
Overall, it is always beneficial (loss-reducing) to minimize the average Z.
This is best accomplished by keeping impurities out of the plasma by
utilizing clean, low-Z walls that sputter at as low a rate as possible.
In a clean, but non-magnetized plasma, the dominant loss mechanism
is usually thermal conduction to the walls (equations A.6 and A.8 ¨ Figures
and 11), followed by particle diffusion (equation A.15 ¨ Figure 12).
Increasing the ambient magnetic field parallel to the walls inhibits these
losses, but it also gradually increases the loss from Synchrotron radiation
(equation A.5 ¨ Figure 10). From simulations, a compact torus (CT) plasma
can sustain several hundred Tesla before Synchrotron radiation exceeds the
Bremsstrahlung radiation loss rate. This is because the plasma is highly
absorbent to the millimeter-wave spectrum emitted by Synchrotron radiation
and electrically-conductive walls efficiently reflect Synchrotron radiation,
as
well as the fact that Synchrotron radiation is not affected by Z.
Other losses included in the tables are ion Bremsstrahlung (equation
A.10 ¨ Figure 11) and ion Synchrotron (equation A.11 ¨ Figure 11)
radiation, which are comparatively minor to their electron counterparts in
quasi-neutral plasmas. Neutral drag (equation A.9 ¨ Figure 11) is also a
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comparatively small loss, but its inclusion enables prediction of how high a
vacuum is required to sustain a moving plasma with negligible drag loss.
Similarly, simulating sputtering of impurities from the wall (equation A.16 ¨
Figure 12) and tracking magnetic dissipation (equation A.7 ¨ Figure 10)
allow estimation of how many impurities a wall will impart to a transient
plasma and how long its internal magnetic field will last, respectively. The
remaining effects of ion-to-electron kinetic transfer collisions (equation
A.12
¨ Figure 11), product energy ion apportionment (equation A.13 ¨ Figure 11),
product energy ion thermalization (equation A.14 ¨ Figure 12), and particle
thermalization (equation A.17 ¨ Figure 11) are essential to accounting for
the allotment of energy and particles coming from core burn dynamics. In
effect, they determine not the burn rate, but rather how to apportion the
fusion energy coming from the original gain equation A.1, given the state of
the plasma as instigated by an external device.
Once the governing equations are accounted for, it is possible to
perform an optimization of the parameters for the method of the invention.
By way of example, for deuterium gas, a convenient diameter for the starting
and ending CT is 137 and 19 millimeters, respectively. The initial
embedded magnetic field is preferably on the order of 6 1 Tesla and the
minimum initial plasma ion density is approximately 5x1015 particles per
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cubic centimeter. For optimum performance, the ejection speed of the CT
requires a minimum of 4.8x106 meters per second and the minimum amount
of time required for compression is on the order of 2 microseconds.
Having now described the invention in detail in accordance with the
requirements of the patent statutes, those skilled in this art will have no
difficulty in making changes and modifications in the individual parts or
their relative assembly in order to meet specific requirements or conditions.
Such changes and modifications may be made without departing from the
scope and spirit of the invention, as set forth in the following claims.
