Everything about Inertial Electrostatic Confinement totally explained
Inertial electrostatic confinement (often abbreviated as
IEC) is a concept for retaining a
plasma using an electrostatic field. The field accelerates charged particles (either
ions or
electrons) radially inward, usually in a spherical but sometimes in a cylindrical geometry. Ions can be confined with IEC in order to achieve controlled
nuclear fusion.
Approaches to IEC
The best-known IEC device is the
Farnsworth-Hirsch Fusor. This system consists largely of two concentric spherical electrical grids inside a vacuum chamber into which a small amount of
fusion fuel is introduced. Voltage across the grids causes the fuel to ionize around them, and positively charged ions are accelerated towards the center of the chamber. Those ions may collide and fuse with ions coming from the other direction, may scatter without fusing, or may pass directly through. In the latter two cases, the ions will tend to be stopped by the electric field and re-accelerated toward the center. Fusors can also use
ion guns rather than electric grids.
The fusor's popularity is largely due to the fact that simple versions can be built for as little as $500 to $4000 (in 2003 US dollars), making it accessible to hobbyists, science fair contestants and small universities. Even these simple devices can reproducibly and convincingly produce fusion reactions, but no fusor has ever come close to producing a significant amount of
fusion power. They can be dangerous if proper care isn't taken because they require high voltages and can produce harmful radiation (
neutrons,
gamma rays and
x-rays). The basic IEC device has been developed as a commercial
neutron generator for industrial applications: first with the trade name FusionStar and now NSD-Fusion.
Two newer approaches both try to solve a problem found in the fusor, which is that some ions collide with the grids. This heats the grids, sprays high-mass ions into the reaction chamber, pollutes the plasma, and cools the fuel. The
Polywell uses a magnetic field to trap a quantity of electrons, fuel ions are then accelerated directly into the middle where they're trapped by the electron cloud that forms a "virtual electrode". Another modern approach uses a
Penning trap to trap electrons in a system otherwise similar to the Polywell.
In 2001, a Japanese team was able to directly measure the double well of an IEC machine using laser-induced fluorescence.
Critique
According to Todd Rider in
A general critique of inertial-electrostatic confinement fusion systems
, net energy production isn't viable in IEC fusion for fuels other than D-T, D-D, and D-He3, and breakeven operation with any fuel except D-T is unlikely. The primary problem that he discusses is the thermalization of ions, allowing them to escape over the top of the electrostatic well more rapidly than they fuse. He considers his paper optimistic because he assumes that core degradation can be countered.
Nevins makes an argument similar to Rider's in [W.M.Nevins, Phys. Plasmas <2> (10), 3804 (October, 1995)], where he shows that the fusion gain (ratio of fusion power produced to the power required to maintain the non-equilibrium ion distribution function) is limited to 0.1 assuming that the device is fueled with a mixture of deuterium and tritium. A fusion gain of about 10 is required for net energy production. Other fusion researchers such as Rostoker and Monkhorst have disagreed with these analyses, claiming their assumptions don't always apply, and proposing nonthermal schemes that they calculate can produce net power, and theorists at
LANL have proposed a new electrostatic plasma equilibrium that should mitigate this problem. This concept, called
Periodically Oscillating Plasma Sphere (POPS)
, has been confirmed experimentally. POPS oscillation maintains equilibrium distribution of the ions at all times, which would eliminate any power loss due to Coulomb collisions, resulting in a net energy gain for fusion-power generation.
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