Download ppt - Fusion Technology Institute

Comments About Current
Plasma Studies at UIUC
Dr. George H. Miley, Hugo Leon, Atanu Khan, Ben Ulmen,
Guilherme Amadio, William Matisiak, George Chen, Paul Keutelian
Research
Description of the IEC Jet Thruster
Concept
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Spherical plasma diode
– Ground potential on an
outer sphere
– Negative potential on
transparent inner spherical grid
– Ions generated in discharge
region between vacuum
chamber wall grid
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Electron emitters at boundary
and additional electrical grids
near grounded outer sphere
can increase and control
efficiency better localize
generation of ions
Allows device to operate at
much lower gas pressures
Gas Feed
Line
Spherical Vacuum
Chamber
Grid
To Vacuum
Pump
High-Voltage
Feedthrough
High-Voltage
Power Supply
Background
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NASA and other laboratories have worked to develop
advanced Hall Thrusters for future satellite applications.
IEC-jet thruster are able to address both issuesscalability and plasma jet control for
maneuverability.
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Conventional plasma thrusters have undergone much
more experimental study than the IEC-jet thruster.
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Simplicity of IEC-Jet thruster design and thermal
scalability- feasible to quickly develop and test a range of
parameters and exhaust channel designs.
Application of Jet Mode for Thrust
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Novel plasma jet thruster, based on Inertial Electrostatic Confinement
(IEC) technology, -for ultra maneuverable - space thruster for satellite
and small probe thrust operations.
IEC Jet design potential - cover a wide range of powers with good
efficiency while providing plasma jet that can start with large diameter
but be narrowed directionally to focus.
Analogous to planar electrostatic ion thruster "folded" into spherical form.
Electrical efficiency match conventional plasma thrusters;
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design simplicity
reduced erosion giving long life time
reduced propellant leakage losses
high power-to-weight ratio
Low gas leakage & good heat removal make it possible to scale the design
to low power or high power.
IEC Thruster Configuration
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Valley or trough created in
electrostatic potential, and hole cut
into the ground sphere.
Allows high-speed ions to escape in
the form of a plasma jet.
Ions generated near the ground
potential with aid of electron emitters
and additional grids.
Central spherical electrical grid
accelerates ions to core region.
Cylindrical "channel" grid with same
electrostatic potential as the central
spherical grid creates passage for ions
to escape to outside.
IEC Thruster Configuration
Performance Parameters Planar and IEC Ion
Thrusters
Parameter
IEC Ion Thruster
Planar Ion Thruster
Propellant
Xenon
Xenon
Molecular Weight ( amu )
131.3
131.3
Specific Impulse (s )
3000
3000
Thrust (mN)
34
34
Jet Power (W)
500
500
Net accelerating Potential
600
593
Beam Current
832
842
Power Loss to Grid
≤50
50
Power Loss to Bremsstrahlung
Radiation
Greater than planar but still
negligible
negligible
Power loss to Ionization of Propellant
(W)
200-250 W
Input Power
750-800
806
Thruster Efficiency
62-68
62
256 W
Performance & Design
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Losses of power to electrical grids should be lower
Higher densities and temperatures in the central core plasma, but increased losses due
to Bremsstrahlung radiation still negligible .
Energy expenditure per ion for IEC device has not been established experimentally, but
can be estimated.
IEC ion thruster - totally new concept:
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little testing has been carried out on it
exact performance is not firmly established
several issues need to be investigated experimentally and theoretically to develop a reliable
thruster for high power applications.
directly applicable to many basic underlying thruster issues
Performance of the IEC thruster is dependent on three major processes: ionization,
microchannel formation and, redirection of ions into the plasma jet.
The exact thrust and velocity of the plasma jet as well as power losses due to ionization,
thermal radiation, Bremsstrahlung radiation, and grid dissipation need to be measured
in the experimental device.
Additional IEC Jet Applications
Waste Treatment Separation
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Elements can be separated
by mass, charge, electronic
state, or by combinations
Several separation processes
applicable, but further study
needed to select optimal
approach considering
plasma components and
direct energy conversion
Dipole Assisted IEC
The Concept of Dipole-assisted IEC
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An opportunity to enhance the Inertial Electrostatic Confinement (IEC)
fusion exists by introducing magnetic dipole to the IEC chamber.
The dipole fields will increase the plasma density in the center region of
the IEC and the combined IEC and dipole confinement properties will
reduce plasma losses.
The DaIEC uses a dipole magnet in the center of two hemispherical
grids.
Two ion sources inject 40 keV deuterium and helium-3 ion beams
toward the center of the DaIEC.
Magnetic field focus the ion beams by trapping ions along field lines.
Hence, a high density beam-beam fusion region within the center of the
DaIEC.
The charged fusion products of D-He3 fusion reaction (14.7 MeV
protons,4 MeV a particles).
Plus the background plasma ions exit through a magnetic diverter
(nozzle) to achieve thrust.
Summary of PoP Study, and a graph of Electron Density
vs. B-field.
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Magnetic field increases the electron
density by a factor of 16.
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Electron temperature decreases in the
presence of a magnetic field
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Discharge voltage decreases in the
presence of a magnetic field
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The magnetic coil can be used to impose
a potential in the central plasma to
control space charge build up
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Overall, the use of the dipole provides
improved ion beam focusing, ion
confinement, and also appears to
favorably affect the discharge voltage
characteristics.
Photographs verify the dipole focusing effect when the magnetic field is on
The DaIEC can be used in a hybrid mode to produce both
thrust and electricity.
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A key advantage of D-3He DaIEC is that the charged fusion products can be
collimated and directly converted to thrust.
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The charged particles can also be used in a direct energy conversion to
produce the electricity.
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To combine these systems we use the fact that the magnetic field channels
charged particles in two directions – forward and aft from the reactor. The
forward direction is used for electrical production and aft for thrust.
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To prevent particles in the electrical converter from canceling the thrust, a
radial direct collection scheme is proposed.
DaIEC
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The DaIEC is a highly attractive space power/ propulsion fusion concept.
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Due to its physical simplicity and projected high power density, DaIEC is
competitive and exceeds the capability of most other proposed space fusion
systems.
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The specific high power and impulse will make it attractive for cargo and
manned missions throughout the solar system, most notably a manned
Mars mission.
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However, there are significant research and physics issues that must be
resolved before the complete system can become a reality. The next step
should be the achievement of beam-beam fusion.
High-Current, Low-Energy Deuterium Glow Discharge for
Studies of Non-Linear Effects in Plasma Facing Materials
Schematic diagram of glow discharge set up: 1-vacuum chamber; 2-cathode support, 3 – cathode, 4- Mo
anode with holes; 5-15 m thick Be-foil; 6-CR-39 detectors; 7-discharge zone supply; 8-scintillator/X-ray
detector.
High-Current, Low-Energy Deuterium Glow Discharge for
Studies of Non-Linear Effects in Plasma Facing Materials
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Evaluation of DD and DT-reactions at the first wall surface of fusion
reactors like ITER has not considered non-linear processes during high
current, low energy bombardment of the metal first wall.
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Concentrations of D and T atoms embedded in the wall surface increases =
a “target” for bombarding ions.
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Conventional (free space) DD-reaction cross-sections predict the DDreactions are negligible at the low energies (≤2 keV) involved. But, the free
space approximation is not accurate for the conditions involved.
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The DD-reaction yield can be orders of magnitude higher than predicted by
extrapolation of the standard (free space) DD-reaction cross-section to
lower deuteron energies. These enhancement (non-linear) effects came
from a drastic increase in the deuteron screening potential in the crystalline
structure of the metal targets at Ed ~ 1.0 keV, especially at a high deuteron
current density where the ion density in the target can become quite large.
Astrophysical Connection
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Nuclear reactions in astrophysical objects also encounter
screening conditions similar to this. Consequently studies of
metal targets bombarded by low energy accelerators has been
strongly studied by groups such as the European Astrophysical
Lab (LUNA) while time integrated yields become large (hence
limiting wall lifetimes), the instantaneous yields are low.
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Thus the key to accurate measurements involves using high
current bombardment plus special detectors such as CR-39
tracking foils to measure charged particle emission during
bombardment.
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Modified IEC Glow Discharge offers High Currents needed
Summary of Experimental Data
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In accelerator measurements with the Ti-target at 2.5 < Ed < 10.0 keV, the deduced
screening potential is Ue = 65  10 eV . However, for the PGD experiment, the
screening potential is as large as Us=620  140 eV
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Put another way, this experimental enhancement for GD in terms of DD-proton yield
even at Ed=1.0 keV is about nine orders of magnitude larger than that predicted with
bare (B&H) cross-section.
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This striking result illustrates the importance of the higher deuteron/electron
densities in the target (due to the higher currents in the GD)
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In addition to fusion plasma wall effects, these densities are also representative of
Astrophysical conditions. Thus the effect is not only of strong scientific interest, but
of direct importance to ITER type fusion reactors and also to nuclear reaction rates
under astrophysical conditions.
Future Modifications
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Plasma probe diagnostics would be added to measure the energy
distribution of deuterons in glow discharge. This is important to monitor
bombardment conditions for accurate rate calculations.
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Temperature measurements of the target surface versus discharge power
(current, voltage and pulse on-to-off ratio) would be performed using a IR
sensor. This data is needed to accurately calculate the deuteron diffusivity,
which appears to be an important parameter affecting the reaction rate.
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The deuterium concentration in the target would be estimated using a four
probe electrical resistivity measurement at the cathode.
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A dE-ES: surface barrier type detector would be added to supplement CR39 measurements of emitted proton energies. Due to noise problems, this
detection will be best used at higher discharge voltages.
In Development
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Electrostatic analyzer
Interactive 3-D model of IEC
Thank You
DD-reaction enhancement factor calculated with formula
(4) for the Ti target during deuteron bombardment with
accelerator [16] (curve 1) and glow discharge (curve 2).
The solid parts of the curves are corresponded to the
deuteron energy ranges where DD-reaction yield was
measured experimentally.
Experimental yield of 3.0 MeV protons at 0.8 <
Ed < 2.45 keV, normalized to that at Ed = 2.45
keV. The bare cross-section corresponded to
Bosch and Halle approximation to Ed  2.45 keV
is marked by a solid line. The dashed line is a DDreaction yield =in accordance with a screening
potential value Ue = 610 eV.
Table 1
Comparison of High Current, Low Energy D Accelerator and Pulsed GD
I, range
Ed(lab),
keV,
range
Wmax,
[W]
P, mm Hg
T,K,
target
D+
energy
spread
*High
Current
Accelerator
10-40 μA
100.0- 2.0
2.0
5*10-7,
vacuum
100-350
± 1.0%
**Pulsed Glow
Discharge (PGD)
100-600
mA
2.5- 0.40
200.0
2.0-10.0, D2
200-2000
±
10.0%
Parameter
*The accelerator uses a Duoplasmatron (Ed = 50 keV) ion source, decelerating system and magnetic focusing installation ].
**Power supply given a periodic rectangular current pulse. The pulse duration can vary within 100 - 600 μs. The distance
between cathode and anode is varied between 4.0 and 6.0 mm.
Dipole-Assisted IEC
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An opportunity to enhance the Inertial Electrostatic Confinement (IEC)
fusion exists by introducing magnetic dipole to the IEC chamber.
The dipole fields will increase the plasma density in the center region of
the IEC and the combined IEC and dipole confinement properties will
reduce plasma losses.
To demonstrate that a hybrid Dipole-IEC (DaIEC) a first model DaIEC
experiment was benchmarked against a reference IEC.
A triple Langmuir probe was used to study the electron temperature
and density.
Adaptation to Propulsion Unit
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Achievement of a beam-beam device requires two key principles:
– beam compression via focusing
– reduction of the background gas pressure
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The first objective can be achieved based on the results obtained in the PoP
project and applies a dipole magnetic field to create sharply focused beam
ions in the IEC chamber. External control of the potential of the virtual
anode formed in the compressed beam region is achieved by biasing the
dipole coil potential to keep it near the accelerating grid potential.
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The second goal of achievement of low background pressures will be
achieved using external ion injectors.
Ion Injection can be used to achieve low background pressure, enabling BeamBeam reactions. An RF Ion Gun developed earlier at UIUC forms the basis for this
concept.
magnetic focusing lens
coaxial copper resonator: hollow cylindrical
stainless steel flange
ceramic (insulator)
upper plasma stream: floating
negative potential
D2 gas feed
ion beam
positive wall,
part of vacuum chamber
magnetic differential coils
helical antenna
glass tube
RF generator
lower plasma stream: floating
A schematic of the Ion BeamTM is shown on the right. The photo on the left shows a 3-D mm hole cut into solid
stainless ball placed 20 cm from the nozzle of the Ion Beam TM.
Fusion Ship II Concept
Clearly, the higher specific power and specific impulse offered by a
DaIEC system significantly reduces mission times.
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Specific Impulse Variations for a (a) manned Mars mission; (b)
Triton sample return mission
Mission Considerations
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The thrust-to-weight ratio of a DaIEC propulsion system is
too low for surface-to-orbit missions. Launched from a
space platform is envisioned.
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The DaIEC is ideally suited for cargo and manned
interplanetary missions due to the very high specific
power (thrust power/ propulsion system mass) and
specific impulse (average exhaust velocity normalized by
earth’s surface gravity).
Star Mode
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Under certain grid voltage, gas
pressure, gas type, and grid
configuration conditions, high
density ion and electron
beams will form in the IEC
device, initiating the "star
mode" of operation.
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In this mode, high-density
space-charge-neutralized ion
beams, "Microchannels,"
pass through open spaces
between grid wires.
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Discovered by U of I
Researchers