Inertial electrostatic confinement
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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.
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[edit] Approaches to IEC
The best-known IEC device is the Farnsworth-Hirsch Fusor.[1] 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 is not taken because they require high voltages and can produce harmful radiation (neutrons, gamma rays and x-rays).
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 are 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.[2][3]
[edit] Critique
According to Todd Rider in A general critique of inertial-electrostatic confinement fusion systems, net energy production is not 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.
[edit] References
- ^ R. Hirsch, "Inertial-Electrostatic Confinement of Ionized Fusion Gases," Journal of Applied Physics 38, 4522 (1967).
- ^ R.W. Bussard, "Some Physics Considerations of Magnetic Inertial-Electrostatic Confinement: A New Concept for Spherical Converging-flow Fusion," Fusion Technology 19, 273 (1991).
- ^ D.C. Barnes, R.A. Nebel, and L. Turner, "Production and Application of Dense Penning Trap Plasmas," Physics of Fluids B 5, 3651 (1993).
[edit] External links
- University of Wisconsin-Madison IEC homepage
- From Proceedings of the 1999 Fusion Summer Study (Snowmass, Colorado):
- Inertial-Electrostatic Confinement (IEC) of a Fusion Plasma with Grids
- Fusion from Television? (American Scientist Magazine, July-August 1999)
- Todd Rider's 1994 Masters Thesis
- Talk by Dr. Robert Bussard, former Asst. Director of the Atomic Energy Commission and founder of Energy Matter Conversion Corporation (EMC2):
- Should Google Go Nuclear? Clean, cheap, nuclear power (no, really) Google Tech Talk November 9, 2006.
- 'The Advent of Clean Nuclear Fusion: Superperformance Space Power and Propulsion' cited in the Dr. Bussard's Talk. 57th International Astronautical Congress 2006 Author: Dr. Robert W. Bussard
