DOW-UAP-D146, AAWSAP DIRD, Aneutronic Fusion Propulsion II, November 2010

This document is a Defense Intelligence Reference Document (DIRD), a technical reference format used by the Defense Intelligence Agency (DIA) to capture baseline knowledge on a specific topic for later analytic use. DIRDs are best understood as reference and synthesis products rather than as original research. It is one of 38 DIRDs produced under the Advanced Aerospace Weapon System Applications Program (AAWSAP) between 2009 and 2011. Because AAWSAP’s scope permitted a broad range of supporting topics, not every DIRD in the series directly concerns aerospace systems or future threat assessment. The following summary reflects the DIRD’s scope and framing at the time of writing and should not be read as implying current validation of the concepts discussed. This DIRD revisits aneutronic fusion propulsion in a more systems-oriented manner, arguing that fusion concepts using low-neutron fuels such as proton-boron or helium-3 could become attractive for space propulsion because they reduce shielding burdens and may support direct conversion of charged-particle energy into thrust or onboard power. The report reviews the relevant fusion plasma physics and focuses on several candidate confinement approaches, then connects those concepts to possible applications in near-space, orbital, and interplanetary propulsion. It presents the most plausible nearer-term use as very high-power electric or plasma propulsion for satellites and deep-space missions rather than atmospheric flight or interstellar travel, while emphasizing that major obstacles remain in ignition, sustained confinement, system mass, power handling, fuel storage, launch integration, and end-to-end engineering.

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Defense
Intelligence
Reference
Document
Defense Futures
01 November 2010
! COD : 20 July 2010
DIA-08-1011-004
Aneutronic Fusion Propulsion
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(U) Aneutronic Fusion Propulsion
The Defense Intelligence Reference Document provides nonsubstantive but
authoritative reference information related to intelli ence to ics or methodolo ies.
Prepared by:
Technology Warning Division (DW0-4)
Defense Warning Office
Directorate for Analysis
Defense Intelligence Agency
Authors:
AAP Person 85, AAP Person 88, AAP Person 89
COPYRIGHT WARNING: Further dissemination of the photographs in this publication is not authorized.
This product is one of a series of advanced technology reports produced in FY 2010 under the Defense
Intelligence Agency, Defense Warning Office's Advanced Aerospace Weapons System Applications
CMWSA} program Comments or questions pertaining to this document should be addressed to
!AAP Person 1 }\AwsA Program Manager, Defense Intelligence Agency, ATTN: JUIAF -
DI/DWO-3, Bldg 6000, Washington D.C. 20340-5100.
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Contents
Chapter 1: Concept Overview ................................................................................ 1
Chapter 2: Fusion Plasma Physics ......................................................................... 3
2.1 Magnetic Confinement............................................................................ 5
2.2 Inertial Confinement .............................................................................. 7
2.3 Electrostatic Confinement ...................................................................... 8
2.4 Magneto-Inertial Confinement ............................................................... 9
Chapter 3: Fusion Propulsion .............................................................................. 11
3.1 Fusion Reactors for Propulsion............................................................. 11
3.2 Air Propulsion ...................................................................................... 13
3.3 Ion Propulsion ..................................................................................... 14
3.4 Plasma Thruster ................................................................................... 14
Chapter 4: Applications ....................................................................................... 17
4.1 Near Space ........................................................................................... 17
4.2 Earth Orbit ........................................................................................... 17
4.3 Interplanetary...................................................................................... 18
4.4 Interstellar........................................................................................... 19
Chapter 5: Recent Developments ........................................................................ 21
5.1 U.S. DOE Programs............................................................................... 21
5.2 International Programs........................................................................ 21
5.3 NASA Programs.................................................................................... 23
5.4 Privately Funded Programs .................................................................. 23
Chapter 6: Future Developments ......................................................................... 25
6.1 Near-Term Developments .................................................................... 25
6.2 Mid-Term Developments ...................................................................... 27
6.3 Far-Term Development......................................................................... 28
Chapter 7: Conclusions........................................................................................ 30
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Chapter 8: Endnotes............................................................................................ 31
Figures
Figure 1. Fusion Reaction Cross Sections vs. Temperature..................................... 4
Figure 2. Magnetic Mirror Confinement .................................................................. 6
Figure 3. a) Tokamak and b) Stellarator Confinement............................................ 6
Figure 4. Field-Reversed Configuration .................................................................. 7
Figure 5. IEC Fusor and Polywell Confinement Configurations ............................... 8
Figure 6. Magnetized Target Fusion Experiment at LANL...................................... 10
Figure 7. Dense Plasma Focus (Lawrenceville Plasma Physics)............................ 10
Figure 8. Specific Power as a Function of Plasma Temperature of Fusion Rocket. 11
Figure 9. Colliding Beam Fusion Reactor .............................................................. 12
Figure 10. DPF Thruster System With Direct Conversion ...................................... 12
Figure 11. Magnetized Target Fusion Reactor ...................................................... 13
Figure 12. MHD Air-Breathing and Fusion Rocket Aerospace Plane ...................... 13
Figure 13. Design of an IEC Jet Thruster - Experimental Device........................... 18
Figure 14. Comparison of Fusion, Nuclear-Thermal, and Chemical Propulsion for
Same Payload....................................................................................................... 19
Figure 15. Thrust-to-Weight Ratio and Exhaust Velocity Regimes for Various Long-
Range Space Propulsion Options.......................................................................... 19
Figure 16. Bussard Ram let.................................................................................. 20
Figure 17. Progress in Tokamak Magnetic Confinement Fusion ............................ 22
Figure 18. ITER Design Concept With BWR Size and Blanket Segment ................. 23
Figure 19. Experiments To Prove a Plasma Fusion Propulsion Concept ................ 28
Figure 20. Roadmap to Aneutronic Fusion Propulsion Development..................... 29
Tables
Table 1: Principal Fusion Reactions...........................................................................3
Table 2: Fusion Peak Interaction Temperatures and Fusion Energy to X-rays.........4
Table 3: Fusion Ignition Temperatures.....................................................................5
Table 4: Advanced Fusion Concept Reactor Companies..........................................24
Table 5: Emerging Technologies..............................................................................26
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Aneutronic Fusion Propulsion
Summary
Controlled fusion energy production has been under development for 60 years.
The primary objective has been gaining the ability to create terrestrial power
plants using deuterium and tritium as fuel. Unfortunately, this objective has
been eluded for both technical and economic reasons. However, the threshold
for achieving success in applying fusion to propulsion is considerably relaxed,
especially if fuels are used that do not use tritium. Tritium has to be
continuously bred; these reactions yield fast neutrons, which require shielding
and cause structural materials to be periodically replaced. Such "aneutronic"
fusion fuels, such as hydrogen fusing with Boron-11, have been studied
extensively for space propulsion applications since the 1980s.
This report reviews the basic fusion plasma physics, design concepts that
apply aneutronic fusion for propulsion, and the requirements for transitioning
to space. The predominant concepts studied include magnetic field reversed
configuration, dense plasma focus and inertial electrostatic confinement. All of
these concepts have venture capital funded programs for terrestrial fusion
power. When applied to space or near-space propulsion, they can exceed the
performance of any conventional electric thruster.
The future technology development of aneutronic fusion propulsion will
initially be motivated by the very large GEO satellites that will be developed in
the next 20 years for commercial and military broadband communication.
Further development of very-high-power propulsion systems(> 100 kW) to
Mars and beyond will require major developments in all technology areas for
confinement pulsed power and ion fuel beam accelerators.
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Chapter 1: Concept Overview
Controlled thermonuclear fusion has been the aspiration for nuclear scientists and
engineers for the last 60 years. During that time, tens of billions of dollars have been
invested in this endeavor with the expected fruition being pushed even further into the
future. When Lyman Spitzer invented the Stellarator in 1951, it was expected to take
only 5 years of concentrated plasma physics experiments to harness the fusion of
hydrogen ions confined by magnetic fields. However, the numerous new instabilities
that arose under increasing higher magnetic confinement pressures have been a
roadblock to the success of controlled fusion.
In 1983, a rediscovery was made by Robert Bussard of a fusion device invented by
Robert Hirsch in his 1966 Ph.D. thesis. The Fusor, as Hirsch named it with his thesis
advisor and famous inventor Philo Farnsworth, simply used spherically concentric
electrodes in a vacuum chamber. When a deuterium gas was supplied to the chamber
and a few-microsecond pulse at 30 kV was applied to the electrodes, D-D fusion
occurred, releasing He and neutrons. Although it released less energy than was needed
to supply the initial electric pulse, it provided the evidence for a method to obtain
supplementary heating to ignition of magnetically confined plasmas.
The Fusor led to continued development of what is now called Inertial Electrostatic
Confinement (IEC) devices. Amongst these was the Dense Plasma Focus (DPF), a
plasma production tube invented in 1961, and several other devices. Magnetic
confinement devices utilized the IEC method with imploding layers of lithium or
applying intense beams from either end of a linear magnetic pinch device. This
resurgence of alternate confinement concepts was immediately applied to fusion space
propulsion since it was recognized that there would be an advantage over nuclear
fission propulsion with its costly safety requirements. For mitigating shielding mass and
tritium fuel launch-safety concerns, non-neutron-generating "aneutronic" fusion fuels
were also adopted.
Aneutronic fusion fuels include those isotopes of light elements that when fused
produce no neutrons or a very few from the fusion of daughter products. Although there
are eight such reactions for light nuclei, the most practical for fusion reactors include
the following:
D + 3He ➔ 4He + p
P + 7Li ➔ 24He
In Chapter 2, we will review the fusion plasma physics needed to apply these
aneutronic reactions to a confinement device to make a fusion reactor practicable for
propulsion, which is described in Chapter 3. In Chapter 4, the relevance of these
aneutronic fusion propulsion concepts will be reviewed and assessed for aerospace
applications including near-space, orbital, and interplanetary propulsion, as well as the
potential for interstellar use. In Chapter 5, we will summarize the recent national,
international, and privately funded R&D that may expedite development, while in
Chapter 6, we outline an R&D path forward for the aneutronic fusion technologies and
systems needed for the next 50 years. Finally, we provide a summary in Chapter 7 that
that conveys aneutronic fusion propulsion:
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• May have near-term applications to replace current satellite ion thrusters and
extend application to interplanetary flight.
• Requires extensive technology development for air and near-space applications.
• Will not be practical beyond the solar system unless breakthrough propulsion
physics can assist the flight to the next stellar system, where fusion "ion
thrusters" can then be used.
Despite the attention propulsion has gotten from the scientific community, the problem
has been insufficiently addressed by the space science community. Although it is
certainly true that the fusion drive train must be successful from a theoretical and
experimental perspective before consideration for adaptation to the space environment,
many critical aspects such as Earth-based launch, space-based assembly, space
materials science, safe flight operations, and mission success need to be introduced
early in the design phase. More importantly, now that these fusion propulsion concepts
are starting to look both feasible and attractive, the transition to space and the inherent
aerospace application development need considerable focus.
Toward this consideration, we now begin with a background on plasma physics that
includes fusion efficiencies and confinement schemes for aneutronic fusion, which leads
us to the application to the propulsion concept discussions that follow.
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Chapter 2: Fusion Plasma Physics
At the most basic level, nuclear fusion occurs by forcing atomic nuclei close enough so
that the attractive strong force (which binds nuclei together) overwhelms the very
powerful electromagnetic repulsion force. Under such circumstances the nuclei fuse
together to form a single nucleus, creating an atom of a different element (along with
byproducts such as radiation and neutrons). Because the strong force dominates over
such short-length scales ( ~10-15 meter, the diameter of a medium-sized nucleus), the
fusion of heavier nuclei are inherently more unstable, with smaller binding energies. For
light nuclei, the binding energies of the individual nuclei are significantly smaller than
that of the fused nucleus; it is the released energy of the fusion process (in the form of
high-energy photons or kinetic energy of nuclear products such as neutrons) that is
sought as an energy source. Table 1 shows Fusion reactions including the relevant
aneutronic fusion reactions.
Table 1: Principal Fusion Reactions
E (MeV)
Main ,,rro/1 d I i 11 ue/
+T-a:+ n 17.5
T +p
+ { 3 Hc + n
+y
T + T - a:+_n
d1•a,1 edfu i II fuel
+ ~, +
C--+ p
p+ Li-+ a,+ H
r>+7 i- 0"
r>+ II - 30'
To fuse a sufficient number of nuclei within a span of time for practical use, it is
generally necessary to heat an ensemble of atoms to the very high energies shown in
Table 1. These energies (temperatures) are high enough that electrons are stripped
from their associated nuclei, producing a plasma of free electrons and ions. The fusion
reaction cross sections (cr), the prob