Inertial electrostatic confinement

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. One of the earliest proposals for IEC was by Willam C Elmore, et al. in January 1959.

Approaches to IEC

Hirsch–Meeks fusor. The two concentric electrodes can be seen in the center of the reaction chamber. From US patent 3,530,497

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 is popular because simple versions can be built by many people, making it accessible to those that want to explore this field. 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). 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.

Three newer approaches 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. A third approach, dubbed MARBLE, uses electrostatic optics to keep ions on orbits that do not intersect grid wires - the latter also improves the space charge limitations by multiple nesting of ion beams at several energies.

In 2001, a Japanese team was able to directly measure the double well of an IEC machine using laser-induced fluorescence.

Critique

In his master's thesis, Todd Rider (an MIT graduate student) asserted , net energy production is not viable in IEC fusion for fuels other than D-T (deuterium-tritium fusion), D-D (deuterium fusion), and D-He3 (deuterium-helium 3 fusion), 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 do not 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. Inertial-Electrostatic-Confinement Fusion. Furthermore, this is probably the only fusion reactor concept that becomes increasingly efficient as the size of the device shrinks. However, very high transparencies (>99.999%) are required for successful operation of the POPS concept. To this end S. Krupakar Murali et al., suggested that carbon nanotubes can be used to construct the cathode grids. This is also the first (suggested) application of carbon nanotubes directly in any fusion reactor.

See also

• Robert Bussard
• List of plasma (physics) articles

External links

• University of Wisconsin-Madison IEC homepage
  • IEC Overview
• From Proceedings of the 1999 Fusion Summer Study (Snowmass, Colorado):
  • Summary of Physics Aspects of Some Emerging Concepts
• Inertial-Electrostatic Confinement (IEC) of a Fusion Plasma with Grids
• Fusion from Television? (American Scientist Magazine, July-August 1999)
• 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
• Latest Fusion developments (WB-7 - June 2008) based on the work of Dr. Robert Bussard
• Website of FPGeneration, Inc