Defense Intelligence Reference Document Aneutronic Fusion Propulsion(1)

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these methods are discussed below. Fusion reactors for the production of electricity
have been a goal for over 50 years, yet no method has yet achieved "break even,"
where the amount of energy generated by fusion exceeds the energy required to
initiate the fusion process. Fusion methods are o~en compared based on their ability to
"break even."
GRAVITATIONAL CONFINEMENT
To initiate fusion, ions of hydrogen or its isotopes must be heated to high enough
temperatures to increase the likelihood of a fusion reaction occurring during a collision.
Another method is to increase the pressure of an ionized gas to a point where the
number of collisions increase with an enhanced possibility of a fusion collision. This is
the mechanism that stars employ to initiate fusion; for example, if the object were
completely composed of deuterium, the minimum mass needed to generate
gravitational pressures sufficient to initiate fusion would be equivalent to the mass of
the planet Jupiter.
MAGNETIC CONFINEMENT FUSION (MCF)
Deuterium and other ions follow lines of magnetic flux, and tokamaks have been used
to form a magnetic field in the shape of a torus to contain a plasma containing ions for
fusion. Tokamaks contain powerful electromagnets that generate the magnetic field.
Secondary electromagnets induce an electric current into the plasma to heat it to
ignition temperature (ohmic heating). Other methods have been employed to heat the
plasma, including the introduction of radiofrequency energy, magnetic compression,
and neutral beam injection.
INERTIAL CONFINEMENT FUSION (ICF)
The Teller-Ulam thermonuclear bomb was an example of inertial confinement where x-
ray radiation pressure from a fission explosion is used to compress a mixture of
deuterium and tritium to initiate fusion.
The National Ignition Facility in Livermore, California, is an example of a laser-based
ICF system. In this facility, a 287,000-lb, 10-meter-diameter target vacuum chamber
is equipped with a small metal cylinder, or holraum, that contains a 2-mm pellet of D-T
gas or "ice." An assembly of powerful lasers simultaneously fire 4 megajoules of
infrared energy into a device that converts this energy into ultraviolet (UV) energy.
The UV energy impacts the holraum, generating x-rays and rapidly heating the holraum.
This induces an implosion that creates extremely high pressures and temperatures in
the D-T pellet, initiating nuclear fusion. Less than 10% of the initial energy is imparted
to the holraum. This is a pulsed system where multiple holraums and pellets would be
required to sustain energy output.
Other methods can be used to momentarily confine a plasma containing deuterium and
tritium to initiate fusion. For example, instead of lasers, ion beams, electron beams,
and conventional explosives could be employed. Several systems based on electron
accelerators have also been used .. The Farnsworth-Hirsch fusor and the Polywell are
examples of two tabletop devices used to demonstrate fusion.
Another accelerator design is called the Dense Plasma Focus (DPF), where a pulsed
accelerator drives a magnetic field within a diffuse mixture of deuterium and tritium gas
to the top of an anode. When the moving magnetic field reaches the top of the anode,
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