Cold fusion was the first Featured Protoscience (see Archive).

Introduction

Cold fusion is technically the name for any nuclear fusion reaction that may occur well below the temperature required for thermonuclear reactions (millions of degrees Celsius).

There are a number of established processes by which this can occur, although currently none of these can produce more energy than is required to sustain and contain the reaction.

The term is most often used in a more narrow sense: namely, a poorly understood phenomenon in electrolytic cells in which a small (table-top) setup near room temperature and standard atmospheric pressure, which has been controversially suggested produces the fusion of hydrogen (specifically deuterium) atoms into helium.

Types of Cold Fusion

Room temperature

• Electrolytic cell fusion. Fleischmann and Pons used a double-walled vacuum flask for the electrolysis chamber (palladium cathode), so that heat conduction would be minimal. They used an open cell, thus allowing the gaseous deuterium and oxygen resulting from the electrolysis reaction to leave the cell. It was necessary to replenish the cell with heavy water at regular intervals.
• Muon-catalyzed fusion is a well-established and reproducible fusion process which occurs at ordinary temperatures. Because of the energy required to create muons and the fact that muons have limited lifetimes, it is not currently able to produce net energy, and analyses indicate at present that energy production from the reaction is not possible.

Generally cold, locally hot fusion

• The Farnsworth-Hirsch Fusor is a tabletop device in which fusion occurs. This fusion comes from high effective temperatures produced by electrostatic acceleration of ions. The device can be built inexpensively, but it too is unable to produce a net power output. These devices have a valid use however, and are commercially sold as a source of neutrons.
• Antimatter-initialized fusion uses small amounts of antimatter to trigger a tiny fusion explosion. This has been studied primarily in the context of making nuclear pulse propulsion feasible. This is not near becoming a practical power source, due to the cost of manufacturing antimatter alone.
• In Cluster impact fusion, microscopic droplets of heavy water are accelerated to collide with a target, so that their temperature at impact reaches at most 105 kelvins, 10,000 times smaller than the temperature required for hot fusion.
• In sonoluminescence, acoustic shock waves create temporary bubbles that collapse shortly after creation, producing very high temperatures and pressures. If fusion is occurring, it is because the temperature and pressure are sufficiently high to produce hot fusion.

External Links

• Wikipedia article on cold fusion.
• Nature 434, 1057 (28 April 2005) Physicists look to crystal device for future of fusion