break even. The point where the power input of a controlled nuclear fusion reaction (supplied by either external sources or the products of reaction) is equal to the power output. Three conditions need to be met for a sustained fusion reaction to occur. They are:
The confinement time is a measure of the rate at which a system loses energy to its environment. electromagnet. A device that produces a magnetic field using an electric current flowing through a coil of wire, generally wound on a soft iron core. Electromagnets are temporary magnets – when the current is turned off, the magnetism is gone. electromagnetic force. One of the four forces – gravity, strong force, electromagnetic force, weak force – that act on particles. Electromagnetic force acts on charged particles and is made up of electric and magnetic forces (eg, moving magnets produce electric forces and moving electric charges produce magnetic forces). The electric charge that is the source of electromagnetic force can either be positive or negative. Because there are two types of charge, the electromagnetic force can be either attractive or repulsive. Opposite charges attract, like charges repel. Physics theory explains that electromagnetic force is carried by photons (packets of electromagnetic radiation). For more information see The four fundamental forces (ThinkQuest, USA). electronvolts (eV). A measure of energy used for convenience in atomic systems. It is the amount of kinetic energy gained by an electron when it passes through an electrostatic potential difference of one volt. It is equal to one volt (1 volt = 1 joule per coulomb) multiplied by the charge of a single electron (in coulombs). One electronvolt is equal to 1.602×10-19 joule. The energy of a fusion reactor is expressed as megaelectronvolts (MeV: 1,000,000 eV) or gigaelectronvolts (GeV: 1,000,000,000 eV). For more information see Energetic particles (National Aeronautics and Space Administration, USA). E=mc2. E stands for the energy released, m stands for the mass that is converted into energy, and c is the speed of light (300,000 kilometres per second). ionising radiation. Any form of radiation that has sufficient energy to remove electrons from atoms, so producing charged particles called ions. It can consist of high energy particles (electrons, protons or alpha particles) or short wavelength electromagnetic radiation (ultraviolet, X-rays and gamma rays). isotope. One of the different kinds of an atom of the same element. All atoms of an element have the same chemical properties, but the different isotopes have different weights. The different weights are because the isotopes have a different number of neutrons. kilowatt hour. A unit of energy that is normally used to measure the consumption of domestic electricity. The joule (1 watt per second) could be used but the numbers become very large and it is common to use the kilowatt hour (1 kilowatt hour = 3,600,000 joules or 3.6 megajoules). kilowatt, megawatt, gigawatt. The unit of energy is the joule (J) and the unit of power (the rate at which energy is used) in the metric system is the watt (W); a kilowatt is 1000 watts. A watt is a very small amount of power and in most mechanical applications we count power in kilowatts. A kilowatt is about equal to the heat energy put out by a single bar radiator, and is also about equal to the power expended by a person running up stairs. A car engine typically produces 50 to 100 kilowatts. When we consider power generation, we use larger units. A megawatt is 1,000,000 watts or 1000 kilowatts. A typical coal-burning power station produces about 1 gigawatt (1000 megawatts) of power. laser. Light amplification by stimulated emission of radiation. A device that produces a high-intensity, directional, monochromatic beam of light. magnetic fields. Are created by electric currents in wires or electrons moving in orbit around a nucleus. Sources of magnetic fields have a north and south magnetic pole. The SI unit for magnetic field is the Tesla (T). For more information see Magnetism (School for Champions). microwaves. The highest frequency radio waves, with wavelengths between about 1 millimetre and 30 centimetres and frequencies between about 300 gigahertz and 300 megahertz. Microwaves are a type of electromagnetic radiation. Moore's Law. Refers to the advance in computing power per unit cost. Moore's law is based on the observation that the number of transistors on a computer chip, which is a rough measure of computer processing power, doubles every 18 months. A graph plotting the number of transistors on a chip versus time on a log scale is a straight line. The graph plotting transistor size versus time is also a straight line. neutron. A particle having no charge that is a constituent of an atom. It has a mass similar to a proton. nuclear fission. Also referred to as atomic fission. The process by which large nuclei are split into two parts, by bombarding them with neutrons, in order to release large amounts of energy. parts per million. This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Therefore 500,000 ppm is the same as 50 per cent, because 500,000 is half of a million. The concentration of oxygen in unpolluted fresh water is about 8 ppm – only 8 parts of oxygen for every 1 million parts of other substances. superconducting magnet. A type of electromagnet (a temporary magnet formed when an electric current is conducted through a coil of wire). In superconducting magnets, the wire is cooled to a temperature close to absolute zero. At this temperature, there is virtually no resistance to the flow of electricity through the wire. For more information see How electromagnets work (How Stuff Works, USA). superconductor. A substance that has no resistance to the flow of an electric current. Superconductors currently require very low temperatures to function. They can be used for energy storage, storing and retrieving digital information, medical imaging machines and friction free transport. For more information see What is superconductivity? (How Stuff Works, USA) and Superconductor information for the beginner (Superconductors.org). tokamak. For more information see Tokamaks (National Space Research Institute, Brazil). uranium. A radioactive heavy metal. The natural element is a mixture of different isotopes or atomic forms. The isotope uranium-235 is used in nuclear non-breeder reactors.
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Posted February 2007.
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