Note: Descriptions are shown in the official language in which they were submitted.
GENFUS.035CA
SYSTEM AND METHOD FOR PLASMA GENERATION AND
COMPRESSION
Technical Field
The present disclosure relates generally to a system and a method for
generating
plasma and more particularly to a system and a method for generating plasma
and
confining such plasma while compressing it.
Background
Unless otherwise indicated herein, the materials described in this section are
not
prior art to the claims in this application and are not admitted to be prior
art by inclusion
in this section.
Plasma is a state of matter similar to gas in which at least part of the
particles are
ionized. The presence of charged particles (e.g. positive ions and negative
electrons)
makes plasma electrically conductive. Plasma with a magnetic field strong
enough to
influence the motion of the charged particles is called magnetized plasma. A
plasma torus
is a magnetized plasma shaped into a toroidal configuration (donut shape),
with linked
poloidal and toroidal (in some cases) closed magnetic field lines. Toroidal
magnetic field
comprises magnetic field lines that go parallel to a magnetic axis of the
plasma torus. The
toroidal field is generated by a current flowing in a poloidal direction
around the plasma's
magnetic axis. Poloidal magnetic field comprises magnetic field lines that go
around the
magnetic axis of the plasma torus and is generated by a current flowing in
toroidal
direction, parallel to the magnetic axis. As a magnetic field line runs many
turns around
the plasma in the toroidal and poloidal direction, it defines a "flux surface"
at a constant
radius from the plasma's magnetic axis. The extent of linkage of the poloidal
and toroidal
magnetic fluxes defines a helicity of the plasma torus. The magnetic field in
the
magnetized plasma confines plasma energy by suppressing the transit of heat
and
particles from the core of the plasma to its edge. Since the path of charged
particles in a
magnetic field is confined to spirals that travel along field lines great care
should be taken
to ensure that the magnetic field lines run in the toroidal and poloidal
direction but not
along the radial direction to avoid a direct route from the core to the edge
of the plasma.
The plasma torus can have, for example: a spheromak configuration, a Field
Reversed Configuration (FRC), a tokamak configuration, a spherical tokamak
(ST)
-1-
CA 2984756 2017-11-06
GENFUS.035CA
configuration, a reversed field pinch (RFP), a stellarator and any other
configurations of
magnetized plasma.
Controlled thermonuclear fusion is based on the fusion of light nuclei present
in
plasma to form a heavier nucleus. Stabilization and maintaining the plasma in
a stable
configuration is very important for any fusion technology. In the case of
magnetized
plasma configurations, plasma magnetic field (poloidal and/or toroidal field
component)
is a key plasma property related to plasma stability and plasma performance.
Maintaining
a proper magnetic field structure for prolonged time is important in order to
get more
nuclei to fuse. Compressing plasma may increase plasma density and plasma
energy so
that more nuclei get to fuse in shorter time period meaning that compressed
plasma need
to be confined and stable for shorter time period, however compressing the
plasma may
cause destabilization of plasma magnetic structure and destroying plasma
confinement.
Thus it is important to maintain plasma magnetic structure stable during
plasma
compression in order to get nuclei to fuse.
Summary
In one aspect, a system for generating and compressing magnetized plasma is
provided. The system comprises a plasma generator with a first closed end and
an outlet,
and a flux conserving chamber that is in tight fluid communication with the
outlet of the
plasma generator, such that the generated magnetized plasma is injected into
an inner
cavity of the flux conserving chamber. The system further comprises an
elongated central
axial shaft with an upper section positioned within the plasma generator and a
lower
section extending out of the outlet of the plasma generator into the flux
conserver. The
end of the lower section of the central axial shaft is connected to the wall
of the flux
conserver. A gas injection system is provided to inject a gas into the plasma
generator.
The system further comprises a power source that comprises a formation power
circuit
configured to provide a formation power pulse to the plasma generator to
ionize the
injected gas and generate magnetized plasma, and a shaft power circuit
configured to
provide a shaft power pulse to the central axial shaft to generate a toroidal
magnetic field
into the plasma generator and the flux conserving chamber. A plasma
compression driver
configured to compress the plasma trapped in the inner cavity is also
provided. During
compression time period, the shaft power circuit is configured to provide an
additional
shaft current pulse to increase plasma toroidal field in order to maintain a
ratio of
-2-
CA 2984756 2017-11-06
GENFUS.035CA
plasma's toroidal field to plasma's poloidal field at the pre-determined range
during
compression. The system further comprises a controller to control the trigger
time of the
power source to provide the formation power pulse separately from the shaft
power pulse,
such that the shaft current pulse is independently controlled from the
formation current
pulse.
In one aspect, the controller triggers the shaft power circuit prior to the
formation
power circuit such that a pre-existing toroidal field is provided in the flux
conserving
chamber before the formation of the magnetized plasma.
In another aspect, the controller is programmed to provide the additional
shaft
current pulse at a pre-determined time. A timing of the additional shaft
current pulse is
determined based on a triggering time of the compression driver and a
compression
trajectory.
In another aspect, the shaft power circuit is configured such that a profile
shape of
the additional shaft current pulse is designed to increase the plasma's
toroidal field to
match plasma's poloidal field during compression.
In one aspect, a method for generating and compressing magnetized plasma is
provided. The method includes injecting a gas in a plasma generator; providing
a toroidal
field in a flux conserver by flowing a current through a central axial shaft;
providing a
current pulse to the plasma generator to generate a magnetized plasma;
injecting the
magnetized plasma into the flux conserver; compressing the plasma using a
compression
driver and adjusting a shaft current pulse to maintain a ratio of plasma's
toroidal field to
plasma's poloidal field at a predetermined range during compression period.
In addition to the aspects and embodiments described above, further aspects
and
embodiments will become apparent by reference to the drawings and study of the
following detailed description.
Brief Description of the Drawings
Throughout the drawings, reference numbers may be re-used to indicate
correspondence between referenced elements. The drawings are provided to
illustrate
example embodiments described herein and are not intended to limit the scope
of the
disclosure. Sizes and relative positions of elements in the drawings are not
necessarily
drawn to scale. For example, the shapes of various elements and angles are not
drawn to
scale, and some of these elements are arbitrarily enlarged and positioned to
improve
drawing legibility.
-3-
CA 2984756 2017-11-06
GENFUS.035CA
FIG. 1 is a cross-sectional schematic view of an example of a plasma
generation
and compression system showing a plasma generator and a flux conserving
chamber with
a compression driver connected to the flux conserving chamber.
FIG. 2, upper plot, is a graphical presentation of a shaft current pulse in kA
and a
formation current pulse in kA over time in microseconds (p), while a lower
plot is a
graphical presentation of a voltage shaft pulse in kV and a formation voltage
pulse in kV
over time in microseconds (vs).
FIG. 3, upper plot is a graphical presentation of a plasma poloidal field near
central shaft in tesla (T) over time in milliseconds (ms) and lower plot is a
graphical
presentation of a plasma poloidal field near outer wall in tesla (T) over time
in
milliseconds (ms) in one exemplary shot using a system of the present
invention.
FIG. 4 is a graphical presentation of a formation current pulse in kA and a
shaft
current pulse in kA over time in milliseconds (ms) during plasma compression
period.
FIG. 5 left column are schematic cross-sectional views of an example of a
numerical model of a plasma generation and compression system with constant
shaft
current pulse during compression period and right column are schematic cross-
sectional
views of the numerical model of a plasma generation and compression system
with
increased (ramped) shaft current pulse during compression period.
FIG. 6 upper plot is a graphical presentation of a plasma poloidal field in
tesla (T)
over time in microseconds (ps) and lower plot is a graphical presentation of a
plasma
toroidal field in tesla (T) over time in milliseconds (ms) when a shaft
current pulse is
increased during compression period.
FIG. 7 is a graphical presentation of a plasma poloidal field in tesla (T)
over time
in microseconds (vs) when a shaft current pulse is not increased (ramped)
during
compression period.
Detailed Description of Specific Embodiments
FIG. 1 shows one non-limiting embodiment of a plasma generation and
compression system 10 having a plasma generator 12 that is in fluid
communication with
an inner evacuated cavity of a flux conserving chamber 14 (also sometimes
referred to as
a flux conserver 14). The plasma system 10 is at least partially evacuated
using a
pumping system (not shown). The generator 12 is configured to generate a
magnetized
plasma 20 and can have a first (closed) end 11 and an outlet 13 that is in
fluid
communication with the inner cavity of the flux conserving chamber 14. The
plasma
-4-
CA 2984756 2017-11-06
GENFUS.035CA
generator 12 can comprise an inner, formation electrode 15 coaxial with a
longitudinal
axis 19 of the system 10 and an outer electrode 16 that is coaxial to and
surrounds the
inner formation electrode 15 thus forming an annular plasma propagating
channel 17
therein between. The plasma generator 12 can further comprise an elongated
central axial
shaft 30 that extends out of the generator 12 into the flux conserver 14. An
upper section
31 of the central shaft 30 is positioned within the plasma generator 12 while
a lower
section 33 of the shaft 30 extends along the axis 19 into the flux conserving
chamber 14,
such that a second end 30b of the central shaft 30 can be in contact to an end
plate 34 of
the flux conserving chamber 14. A first end 30a of the shaft 30 can be
separated from the
formation electrode 15 forming a gap 32 therein between. In the illustrated
example, the
outer electrode 16, the inner electrode 15 and the upper section 31 of the
shaft 30 have a
slightly tapering configuration toward the outlet 13, such that the plasma
propagation
channel 17 has a tapered configuration as well, meaning that a circumference
of the
plasma propagation channel 17 at the first end 11 is greater than the
circumference of the
channel 17 at the outlet 13. However, person skilled in the art would
understand that the
outer and inner electrodes 16, 15 and the shaft 30 can all have cylindrical
shape forming a
propagation channel 17 with straight configuration without departing from the
scope of
the invention. In one implementation, the outer electrode 16 can have tapered
geometry
while inner electrode 15 and the shaft 30 can have cylindrical geometry and
provide a
plasma propagation channel 17 with a tapered geometry. In the illustrated
example shown
in FIG. 1, the shaft 30 is shaped such that its upper section 31 is generally
conically
shaped while its lower section 33 is generally cylindrical. This is for
illustration purposes
only and the size and the shape of the central shaft is determined based on
the size and
shape of the flux conserver 14 and the parameters of the plasma generator 12.
For
example, the shaft 30 can have generally cylindrical shape through the entire
length or it
can have any other suitable shape or a combination thereof without departing
from the
scope of the invention. The size and the shape of the shaft 30 define the size
and the
shape of a portion of the plasma channel 17 defined as an annular space
between the
central shaft 30 and the outer electrode 16. The flux conserver 14, the axial
shaft 30 and
the electrodes 15 and 16 are made from a conductive and high-vacuum-compatible
material.
In one implementation, the upper section 31 of the shaft 30 can be a liquid
metal
reservoir that contains a liquid metal, and the lower section 33 of the shaft
30 can be a
-5-
CA 2984756 2017-11-06
GENFUS.035CA
liquid metal guide that flows out through the outlet formed in the liquid
metal reservoir,
through the flux conserver 14 and into a catcher (not shown) positioned, for
example,
within the end plate 34. The liquid metal from the catcher can be recirculated
back into
the liquid metal reservoir using one or more pumps. The liquid guide can flow
continuously or the flow can be regulated using a valve that is in
communication with the
reservoir' s outlet.
The flux conserver 14 can comprise an opening that is aligned with the outlet
13
of the plasma generator 12 so that the plasma 20 generated in the plasma
generator 12 can
be injected into the inner evacuated cavity. The flux conserver 14 can further
comprise a
liner 36 that defines the inner evacuated cavity. For example, the liner 36
can be formed
by injecting a liquid medium into the flux conserver 14 forming the evacuated
cavity.
Examples of liquid liners and methods for forming evacuated cavity into the
liquid liners
are described in US patents Nos. 8,891,719, 8,537,958 and US patent
application
publication No. 20100163130. In one implementation, the liner 36 can be a
solid liner,
such as for example a wall of the flux conserver 14 or a solid liner attached
to/coated on
an inner side of the wall of the flux conserver 14.
A series of magnetic coils 18 can be used to form an initial (stuffing)
magnetic
field in the plasma propagation channel 17. For example, some of the coils 18
can be
positioned within the inner electrode 15 while some of the coils 18 can be
positioned
around the outer electrode 16, such that a desired configuration of the
initial stuffing
magnetic field is distributed in the plasma propagation channel 17 before the
formation of
the plasma. The magnetic field lines of the stuffing magnetic field extend
between the
inner and the outer electrodes 15 and 16. Any number of coils 18 can be
provided and
positioned around or within the plasma generator 12 to provide the desired
strength and
configuration of the initial magnetic field. In some implementation, a high
permeability
(e.g. ferromagnetic) core can be included within the inner electrode 15 and/or
within the
axial shaft 30 in order to concentrate initial (stuffing) magnetic field.
A number of gas valves 22 that are in fluid communication with the annular
plasma propagation channel 17 are arranged as a ring around the periphery of
the plasma
generator 12 to symmetrically inject a precise quantity of gas into the
channel 17. Each of
the valves 22 are in fluid communication with a gas reservoir (not shown) and
are
operable to provide a substantially symmetrical introduction of the gas into
the channel
-6-
CA 2984756 2017-11-06
GENFUS.035CA
17 of the plasma generator 12. The injected gas can be for example, one or
more isotopes
of light elements i.e., isotopes of hydrogen (e.g., deuterium and/or tritium)
and/or isotopes
of helium (e.g., helium-3) or any other gas or gas mixture. The system 10
further
comprises a power source 24 which includes at least one capacitor bank. The
power
source 24 can be a pulsed power source configured to provide a discharge pulse
to the
inner electrode 15 so that a current flows from the inner electrode 15, across
the gas to the
outer electrode 16, ionizing the gas and forming plasma.
The coils 18 setup the initial stuffing magnetic field prior to the gas being
injected
into the annular plasma propagation channel 17 and prior to the current being
discharged
between the electrodes 15 and 16. For example, the stuffing magnetic field can
be applied
a few seconds before the discharge. Once the gas diffuses to at least
partially fill the
channel 17, the power source 24 can be triggered causing a formation current
pulse to
flow between the electrodes 15 and 16. The current passes through the gas in a
substantially radial direction, ionizing the gas and forming the plasma. This
current can
create a plasma toroidal magnetic field, and the gradient of the magnetic
pressure can
exert a force (Lorentz force) I x that can cause motion of the plasma down the
annular
channel 17 toward the flux conserver 14. As the plasma moves forward, it
interacts with
the stuffing magnetic field generated by the coils 18. The force that
displaces the plasma
toward the flux conserver 14 has sufficient strength to overcome the tension
force of the
stuffing magnetic field so that the stuffing field is weakened and deformed by
the
advancing plasma (bubbling stage). Eventually the plasma breaks free so that
the
magnetic field can wrap around the plasma forming a magnetized plasma torus 20
with a
poloidal magnetic field and a toroidal magnetic field. The magnetized plasma
20 can be a
toroidal plasma such as for example, a spheromak, a spherical tokamak or any
other
suitable configuration of magnetized plasma.
The central shaft 30 is electrically isolated from the inner electrode 15 and
is
electrically conductive, so that a current flowing through the central shaft
30 generates a
toroidal magnetic field in the plasma generator 12 and the flux conserver 14.
For
example, an additional power source 26 can provide a power pulse to the
central axial
shaft 30. The additional power source 26 can be a pulsed power source. In one
implementation, a single pulsed power source can provide both a formation
power pulse
to the formation electrode 15 and a shaft's power pulse to the central shaft
30 without
-7-
CA 2984756 2017-11-06
GENFUS.035CA
departing from the scope of the invention. For example, the power source can
comprise a
formation power circuit 24 and a shaft power circuit 26. The current provided
by the shaft
power circuit 26 flows along the shaft 30 and back on an inner wall of the
flux conserving
chamber 14 and the outer electrode 16, thus generating a toroidal field within
the plasma
generator 12 and flux conserver 14. The toroidal field formed by the shaft
current flow
has magnetic lines that extend around the central axial shaft 30.
The shaft power circuit 26 can provide the power pulse to the central axial
shaft
30 ahead of the plasma formation pulse thereby creating a toroidal magnetic
field in the
plasma generator 12 and the flux conserver 14 before the formation of the
plasma 20. So,
the plasma formation can occur with a pre-existing toroidal field in the
plasma generator
12 and the flux conserver 14. When the formation pulse is discharged and the
plasma is
accelerated down the plasma generator 12 due to the Lorentz force, it will
push such
preexisting toroidal field deflecting its field lines. This toroidal field can
diffuse into the
plasma and can increase plasma toroidal field. FIG. 2 upper plot shows an
example of a
formation current curve 210 and a shaft current curve 220 while lower plot
shows a
formation voltage curve 212 and a shaft voltage curve 222. As can be noticed
from the
illustrated example, the formation current pulse can be about ¨700 kA for a
duration of
about 90 las, while the shaft current is about 400 kA and is triggered about
110 vt s prior to
the triggering time of the formation current pulse. This is for illustration
purposes only,
and the triggering time of the shaft pulse can be determined depending on the
properties
of the power source 26, desired parameters of the plasma 20 and the size and
geometry of
the plasma system 10. In addition, the shaft current pulse can be set such
that the current
can continue flowing long after the plasma 20 is formed and injected into the
flux
conserving chamber 14, so that the current flowing can put additional toroidal
field into
the plasma. For example, the shaft's current pulse can last about 2 ms while
the formation
current pulse last about 80 vis. The longer shaft current pulse can help in
controlling
plasma stability and confinement by controlling plasma safety factor q. The
safety factor
q can best be described by tracing out a magnetic field line in the plasma and
counting the
number of toroidal turns it completes before completing one poloidal turn. q-
factor at the
plasma's core is in general different than q-factor at the plasma's edge, so q-
profile is
plasma's q-factor along its radius. When q is a rational number (i.e. 1/2, 1,
3/2, 2 etc.) the
plasma will resonate and will develop an asymmetry. Often this asymmetry
rotates
around the torus and can be detected by the phase of signals obtained from a
number of
-8-
CA 2984756 2017-11-06
GENFUS.035CA
sensors as an oscillation in time. Such an asymmetry can reduce the heat
confinement of
the plasma configuration. So, fine tuning and adjustment of the plasma's q-
profile can
result in low plasma fluctuations and improved plasma confinement. Measuring
plasma's
q-profile and its control in real time is complex exercise requiring complex
modeling. However, the inventors have found that the ratio of plasma's
toroidal field to
the poloidal field can be used as a proxy for q-profile measurements. The
ratio of the
toroidal to poloidal field can be controlled and maintained to an empirically
determined
optimum value/range that relates to a predetermined q-value. Control of the
toroidal field
can be achieved by adjusting the shaft current pulse. For example, if the
magnetic field
ratio falls below the empirically determined optimum value, the toroidal field
can be
increased by increasing the shaft current pulse, which will raise the magnetic
field ratio
up, keeping the plasma's q between critical values. For example, the pre-
determined q-
value can be any value different than a rational number, such as for example,
greater than
1 and smaller than 3/2 (1 <q <3/2).
The system 10 can comprise a number of viewing ports at various axial
positions
along the plasma generator 12 and/or flux conserver 14 to accommodate various
measuring probes/detectors. An array of diagnostics can be provided to measure
plasma's
parameters (e.g. magnetic field, temperature, density, impurities), as well as
system's
parameters (e.g. current, voltage, etc.). Plasma magnetic configuration can be
determined
using an array of magnetic probes, such as for example B-dot probes or any
other suitable
magnetic probes. Such magnetic probes can be positioned in the wall of the
central axial
shaft 30, the flux conserver 14, and/or the plasma generator 12 and can be
configured to
provide signals of both the poloidal and toroidal field in the plasma at
various axial/radial
and/or angular positions over time. Each of the magnetic probes can provide
one signal
for plasma's poloidal field and another signal for plasma's toroidal field.
For example,
each of the probes can comprise two separate coils located near probe's tip.
One of the
coils can be oriented so that it will capture the signal of plasma's poloidal
field and the
other coil can be directed to measure plasma's toroidal field. Each of the
probes can be at
different radial, axial and/or angular position so that the magnetic field at
various radial,
axial and/or angular positions can be measured over time. For example, FIG. 3
upper plot
illustrates an example of a plasma poloidal field over time obtained from
different probes
(one curve per probe) positioned on the central shaft 30 (providing signals of
plasma
magnetic field at the inner edge of the plasma) while the lower plot
illustrates the plasma
-9-
CA 2984756 2017-11-06
GENFUS.035CA
poloidal field over time obtained from the probes positioned near the wall of
the flux
conserver (signals od plasma magnetic field at the outer edge of the plasma
torus). The
signals at the upper plot are from probes positioned at the same radial
position (R = 9mm
distance from the longitudinal axis 19 of the flux conserver 14) but different
axial/angular
position, while the signals at the lower plot are from probes positioned at
the wall of the
flux conserver 14 at various radial, axial and angular positions. As can be
noticed, the
plasma poloidal field in proximity to the central axial shaft has peak
poloidal field of
about 0.9 T while in proximity to the outer wall the peak poloidal field is
about 0.25 T.
The poloidal field decays after 1.7 ms, indicating a plasma life of about 1.7
ms. The
signals from the magnetic probes can be used to estimate total toroidal field
ABtor and
total poloidal field ABpoi and determine average q-profile. Being able to
measure and
determine plasma magnetic configuration is important to measure and control
plasma q¨
profile since based on the signals obtained from the magnetic probes one can
adjust the
shaft current pulse in order to keep plasma q-profile within a pre-determined
range.
The system 10 can further comprise a compression driver 21 configured to
compress the plasma 20. For example, the compression driver can comprise a
plurality of
pneumatic pistons that generate a pressure wave in the liquid liner as
described in US
patent application publication No. 20100163130. So the generated pressure wave
converges inward collapsing the inner cavity and compressing the plasma
trapped therein.
In one implementation, the compression driver can be a plurality of pneumatic
valves or
plasma guns or a chemical driver that can compress plasma by pushing the liner
36. Any
other suitable compression driver configured to compress plasma can be used
without
departing from the scope of the invention.
The system 10 can further comprise a controller 23 that is in communication
with
the power source 24, 26, compression driver 21 and diagnostic probes, i.e.
magnetic
probes. The controller 23 can be used to control the timing and duration of
the formation
current pulse, the shaft current pulse and the compression driver 21. The
controller 23 can
comprise an input unit, an output unit and a processing unit. The controller
23 can be
configured to independently control the shaft current circuit 26 and the
formation current
circuit 24.
The shaft power circuit 26 can be designed as a single stage or multi-stage
circuit
to provide and sustain sufficient toroidal field in the flux conserver 14 for
a desired
-10-
CA 2984756 2017-11-06
GENFUS.035CA
plasma configuration. For example, the shaft power source 26 can be designed
as a 2-
stage circuit, such that in the first stage it provides a current pulse that
rapidly reaches
peak current and provides the pre-existing toroidal field before plasma
formation, and a
second stage to maintain the current flow against resistive loses (e.g. the
resistive loses in
the conductors). In some implementations, the shaft power source 26 can
provide an
additional shaft current pulse to increase plasma's toroidal field at pre-
determined time
and for pre-determined duration. For example, if the signals provided by the
magnetic
probes indicate increase of the poloidal field, the controller 23 can trigger
the shaft
current circuit to increase the shaft current. By increasing the shaft
current, the toroidal
field of the plasma 20 is increased, thus maintaining the ratio of the
toroidal and poloidal
field and keeping the plasma q-factor at the pre-determined value. Increasing
of plasma
poloidal field can happen for example, during plasma compression. When the
compression driver 21 is triggered, it compresses the plasma 20 increasing its
poloidal
field thus bringing the plasma q-factor below its pre-determined value (e.g.
plasma q-
factor can hit rational number q = 1) which may destabilize plasma magnetic
field
destroying plasma confinement. In order to maintain plasma stability during
compression
the safety factor q is maintained at a predetermined value/range by increasing
the shaft
current during compression. FIG. 4 shows a formation current pulse 310 and a
shaft
current pulse 320 with time during plasma compression. As can be noticed,
shaft current
is increased/ramped up (see jump 325) during the compression time period 330.
The shaft
current circuit can be configured to increase the shaft current pulse for at
pre-determined
time period until the 'liner 36 that moves inward compressing plasma 20 closes
the outlet
13 (gap formed by the plasma propagation channel 17 at the outlet 13). Once
the outlet 13
is closed, a closed current loop is formed around the plasma 20, trapping the
toroidal field
in the flux conserver 14, so that the toroidal field will continue increasing
at the same rate
as the poloidal field without any further increase of the shaft current from
the shaft power
supply.
FIG. 5 shows examples of a numerical model of the plasma generation and
compression system 10. Examples in the left column are numerical models of the
system
and plasma's confinement and stability behavior during compression when the
central
shaft current pulse is maintained constant during compression period 'shaft
(t) = lo, and in
the right column are models of plasma's confinement and stability behavior
during
compression when shaft's current increases during compression as 'shaft (t) oc
1/r(,), where
-11-
CA 2984756 2017-11-06
GENFUS.035CA
r(t) is radius of the plasma. As can be noticed, when shaft current is
constant during
compression period the magnetic field confining the plasma gets disturbed
destroying the
plasma confinement, while by increasing the shaft current generally
proportionally with
the compression ratio the plasma magnetic field is maintained stable keeping
the plasma
stable during compression.
FIG. 6 shows the magnetic field during one compression experiment when the
shaft current was ramped up to maintain plasma's toroidal to poloidal magnetic
field ratio
at pre-determined range to keep plasma stable during compression. Upper plot
shows
plasma poloidal field while the lower plot shows plasma toroidal field for the
same shot.
As can be noticed the signals obtained from the magnetic probes during
compression are
smooth and overlapping (no oscillation) indicating a stable plasma magnetic
field during
compression.
FIG. 7 depicts plasma magnetic field during a compression experiment when the
shaft current is not ramped up showing deviating (oscillations) magnetic field
signals 600
which indicates that the plasma magnetic structure is destabilized. Thus,
ramping up the
shaft current during compression period keeps the plasma stable during
compression.
The increase of the shaft current pulse during compression can be done
actively in
real time by monitoring the signals from the magnetic probes. The controller
23 can
process the signals obtain from the magnetic probes in real time and when an
increase in
the plasma poloidal field is detected the controller can trigger the shaft
power circuit to
increase the shaft current pulse to match the increase of the poloidal field.
In another
implementation, the controller 23 can be programmed to trigger the shaft
current circuit to
increase the shaft current at pre-determined time based on a triggering time
of the
compression driver 21 and compression trajectory (e.g. trajectory of the liner
36 over time
during compression). In one embodiment, the increase of the shaft current
pulse can be
triggered before the compression period, so that the toroidal field generated
by the shaft
current can diffuse into the plasma and thus match the raise in the poloidal
field. For
example, the additional (ramp) current pulse can be triggered 10 ¨ 150 is1
before the
liner's wall moves inward (start of the compression). In one embodiment, the
additional
shaft current pulse can match the trigger time of the compression driver 21.
FIG. 6 lower
plot shows that the additional shaft current pulse was triggered about 10 s
ahead of the
liner wall moves (start of the compression). More than one additional shaft
current pulses
-12-
CA 2984756 2017-11-06
GENFUS.035CA
can be provided during compression period to match the profile of the poloidal
field curve
and keep the plasma stable. FIG. 6 lower plot indicates that five additional
shaft current
pulses were triggered to keep the toroidal field increasing as the poloidal
field increases
due to plasma compression. However, person skilled in the art would understand
that the
shaft power source can be configured so that it can provide a single
additional shaft pulse
with a desired profile. The compression trajectory (e.g. trajectory of the
liner 36) can be
determined experimentally or analytically and a timing table for the shaft
current circuit
can be fed into controller 23 so that the additional shaft current pulse can
be pre-set based
on the trigger time of the compression driver 21 and the compression
trajectory.
The plasma obtained in any of the disclosed embodiments can be a high energy
plasma and can be suitable for applications such as, e.g., production of
medical isotopes,
neutron source, x-ray radiation source, nuclear fusion devices, etc. Certain
embodiments
of the system may be configured and operated to act as neutron generators or
neutron
sources. Neutrons so produced have a wide range of practical uses in research
and
industrial fields. For example, a neutron source can be used for neutron
activation
analysis (NAA) which can provide multi-element analysis of major, minor,
trace, and rare
elements in a variety of substances (e.g., explosives, drugs, fissile
materials, poisons, etc.)
and can be used in a variety of applications (e.g., explosive detection and
identification,
ecological monitoring of the environment or nuclear waste, etc.). Embodiments
of the
system configured as a neutron source can also be used for materials research
(e.g.,
analyzing the structure, dynamics, composition, and chemical uniformity of
materials),
for non-destructive testing of industrial objects (e.g., via neutron
radiography and/or
neutron tomography), and for many other industrial and technological
applications.
While particular elements, embodiments and applications of the present
disclosure
have been shown and described, it will be understood, that the scope of the
disclosure is
not limited thereto, since modifications can be made without departing from
the scope of
the present disclosure, particularly in light of the foregoing teachings.
Thus, for example,
in any method or process disclosed herein, the acts or operations making up
the
method/process may be performed in any suitable sequence and are not
necessarily
limited to any particular disclosed sequence. Elements and components can be
configured
or arranged differently, combined, and/or eliminated in various embodiments.
The
various features and processes described above may be used independently of
one
-13-
CA 2984756 2017-11-06
GENFUS.035CA
another, or may be combined in various ways. All possible combinations and sub-
combinations are intended to fall within the scope of this disclosure.
Reference
throughout this disclosure to "some embodiments," "an embodiment," or the
like, means
that a particular feature, structure, step, process, or characteristic
described in connection
with the embodiment is included in at least one embodiment. Thus, appearances
of the
phrases "in some embodiments," "in an embodiment," or the like, throughout
this
disclosure are not necessarily all referring to the same embodiment and may
refer to one
or more of the same or different embodiments.
Various aspects and advantages of the embodiments have been described where
appropriate. It is to be understood that not necessarily all such aspects or
advantages may
be achieved in accordance with any particular embodiment. Thus, for example,
it should
be recognized that the various embodiments may be carried out in a manner that
achieves
or optimizes one advantage or group of advantages as taught herein without
necessarily
achieving other aspects or advantages as may be taught or suggested herein.
Conditional language used herein, such as, among others, "can," "could,"
"might,"
"may," "e.g.," and the like, unless specifically stated otherwise, or
otherwise understood
within the context as used, is generally intended to convey that certain
embodiments
include, while other embodiments do not include, certain features, elements
and/or steps.
Thus, such conditional language is not generally intended to imply that
features, elements
and/or steps are in any way required for one or more embodiments or that one
or more
embodiments necessarily include logic for deciding, with or without operator
input or
prompting, whether these features, elements and/or steps are included or are
to be
performed in any particular embodiment. No single feature or group of features
is
required for or indispensable to any particular embodiment. The terms
"comprising,"
"including," "having," and the like are synonymous and are used inclusively,
in an open-
ended fashion, and do not exclude additional elements, features, acts,
operations, and so
forth. Also, the term "or" is used in its inclusive sense (and not in its
exclusive sense) so
that when used, for example, to connect a list of elements, the term "or"
means one,
some, or all of the elements in the list.
Conjunctive language such as the phrase "at least one of X, Y and Z," unless
specifically stated otherwise, is otherwise understood with the context as
used in general
to convey that an item, term, etc. may be either X, Y or Z. Thus, such
conjunctive
-14-
CA 2984756 2017-11-06
GENFUS.035CA
language is not generally intended to imply that certain embodiments require
at least one
of X, at least one of Y and at least one of Z to each be present.
The example calculations, simulations, results, graphs, values, and parameters
of
the embodiments described herein are intended to illustrate and not to limit
the disclosed
embodiments. Other embodiments can be configured and/or operated differently
than the
illustrative examples described herein.
-15-
CA 2984756 2017-11-06
