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=============================================================== Glossary Part 9: Terms beginning with "I" FREQUENTLY USED TERMS IN CONVENTIONAL FUSION RESEARCH AND PLASMA PHYSICS Edited by Robert F. Heeter, firstname.lastname@example.org Guide to Categories: * = plasma/fusion/energy vocabulary & = basic physics vocabulary > = device type or machine name # = name of a constant or variable ! = scientists @ = acronym % = labs & political organizations $ = unit of measurement The list of Acknowledgements is in Part 0 (intro). ================================================================== IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII # I: variable used to indicate total current through a conductor. @ IAEA: International Atomic Energy Agency; see entry @ IBHP: Integrated Biological Hazard Potential; see entry @ ICE: Ion Cyclotron Emission; see entry @ ICF: Inertial Confinement Fusion; see entry @ ICH: Ion Cyclotron Heating - see ICRH @ ICRF: Ion Cyclotron Range of Frequencies @ ICRH: Ion Cyclotron Resonance Heating; see entry @ IEEE: Institute of Electrical and Electronic Engineers; see entry @ INEL: Idaho National Engineering Laboratory; see entry @ IPP: Max Planck Institute for Plasma Physics; see entry @ IR: Infrared (region of the electromagnetic spectrum) @ ITER: International Thermonuclear Experimental Reactor; see entry % Idaho National Engineering Laboratory: U.S. Department of energy laboratory involved in engineering studies for fusion and fission reactors, among other things. Not surprisingly, located in Idaho. * Ignition: In fusion, as in an ordinary (chemical) fire, ignition is the point where the temperature and confinement of heat in the fuel (plasma in the case of fusion) are such that energy released from ongoing reactions is sufficient to maintain the temperature of the system, and no external heating is needed. An ignited fusion plasma produces so much energy from fusion reactions that the plasma is fully heated by fusion reaction products (alpha particles in the case of D-T fusion), and the plasma no longer needs any external source of power to maintain its temperature. (The plasma may, however, still need something to maintain its confinement; this gives us control over the fusion reaction and helps prevent fusion reactors from having "meltdown" problems like fission reactors.) * Ignition Temperature: For given values of density and energy confinement, the temperature at which ignition occurs. (see ignition above) > Impact Fusion: Fusion approach where a "fuel" projectile is acclerated and impacted into either a stationary target or another projectile. (Valuable for scientific purposes but not a candidate for a fusion energy source because the likelihood of fusion occurring in a single collision is too low. Multiple accelerated pellets colliding with spherical symmetry might be a viable inertial confinement approach, though.) * Impact fusion drivers: macroparticle/projectile accelerator which could be used in inertial confinement fusion. * Impurities: atoms of unwanted elements in the plasma, which tend to degrade plasma performance, and in the case of fusion plasmas tends to inhibit fusion ("poisoning the reactor"). See also poisoning. * Impurity Control: Processes which reduce or control the level of impurities in a plasma, and thereby improve its quality; see also wall conditioning. * Inboard side: portion of a tokamak (or other toroidal device) closest to the central axis. (As distinguished from "outboard side.") * Incoherent scattering: Type of scattering in which the scattering elements act independently, so that no definite phase relationships exist among the different parts of the scattered beam (particles or photons). & Index of Refraction: For a given wavelength, this is the ratio of the velocity of light in vacuum (c) to the velocity of light in a refractive material (e.g., glass, plasma, etc.). & Inductance: Characteristic relating the magnetic flux generated through a loop of wires to the current in the wires; Phi=LI. & Induction: A changing magnetic flux through a current loop will induce an electric field which will drive a current through the loop. This is the principle behind an AC transformer, where an oscillating electric voltage in one loop of the transformer creates a current which generates an oscillating magnetic field, which then induces a different voltage and current in a second loop. * Inductive Current Drive: Method to drive current in a toroidal plasma by using the torus of conducting plasma as the second coil in a transformer. The primary coil usually runs down the center of the torus; changes in the current driven through the primary coil create changing magnetic fields which drive current in the plasma. The current thus driven can be used to heat the plasma as well (see also ohmic heating; induction). * Inertial Confinement Fusion: Approach to fusion where the plasma is imploded so quickly that the inertia of the converging particles is so high that many fuse before they disperse. This is the method used in a hydrogen bomb; ICF schemes for power production usually use small pellets of fuel in an attempt to make "miniature" h-bomb type explosions. Methods for imploding the pellet include bombardment from all sides with high-powered laser and particle beams, and of course implosion in a fission bomb. Parts of ICF fusion research remain classified due to their military implications and applications, though much ICF research was recently declassified. * Instability: A state of a plasma (or any other physical system) in which a small perturbation amplifies itself to a considerable alteration of the state of the system. In plasmas instabilities sometimes leads to disruptions (see entry). Most instabilities are associated with waves and other natural modes of oscillation in the plasma, which can sometimes grow. There are (unfortunately!) many kinds. See also: Flute instability, MHD instability, Interchange instability, microinstability, kink instability, resistive instability, trapped particle instability, two-stream instability, universal instability, and velocity-space instability. % Institute of Electrical and Electronic Engineers: Professional society for this branch of engineering. * Integrated Biological Hazard Potential (IBHP): Total biological hazard potential of a collection of radioactive materials summed over their decay lifetimes. See also BHP. One measure of the IBHP is the amount of water one would need to use to dilute the materials to the point where the water would be safe to drink. * Integrated neutron flux: Sum (integral) of the neutron flux (neutrons per unit time per unit area, see flux) over all time; total number of neutrons which passed through a unit area. Important figure-of-merit in testing effects of neutron radiation on materials, and in assessing how long such materials can survive exposure to neutron sources (such as fission reactor cores and D-T fusion plasmas). * Intensity: This term has different meanings in different contexts. Can refer to the amount of power (energy per unit time) incident on a unit surface area, or flowing through a unit volume. Can refer to the number of particles or photons incident, per unit time, on a unit area, or flowing through a unit volume. Also, for an amount of a radioactive material, intensity can refer to the number of radioactive disintegrations per unit time. * Interchange Instability: In the simplest form, if you place a high-density fluid on top of a low density fluid, gravity will pull the high density fluid downwards so that the low-density fluid ends up on top. The two fluids therefore interchange places. More generally, an interchange instability occurs when two types of fluid are situated with an external force such that the potential energy is not a minimum; the two fluids will then interchange locations to bring the potential energy to a minimum. In plasmas with magnetic fields, the plasma may interchange position with the magnetic field. A prime example is the flute instability in mirror machines. (See MHD, instability, flute, mirror.) * Interference: When two waves propagate through the same region of space, they interfere with each other. Neither wave is altered, but the amplitudes of the waves add (or cancel, if they're of opposite sign) to give the total effect to the medium at that point. * Interferometer: Device which measures changes in a medium by looking at effects on the interference of two waves which are passed through that medium. See interferometry, laser interferometer, optical inteferometer, Fabry-Perot interferometer, microwave interferometer. * Interferometry: Method of gathering information about a medium by using an interferometer or similar technique. Optical - Uses light as the wave to be interfered. Microwave - Uses microwaves instead. Microwave interferometry is especially useful in plasma physics for measuring plasma densities. > Internal ring devices: Toroidal configurations in which current-carrying rings are suspended (either mechanically or magnetically) inside the plasma chamber. % International Atomic Energy Agency: (from Herman) An autonomous intergovernmental organization established in 1956 with the purpose of advancing peaceful uses of atomic energy, with headquarters in Vienna. > International Thermonuclear Experimental Reactor (ITER): Huge fusion reactor being planned by the EC, US, Japan, and Russia (former USSR?). Should generate far more energy than it consumes. Research goals include engineering studies of reactor materials, component designs for steady-state devices, and testing/proving commercial feasibility. Discussed in sections 5 and 9. * Ioffe Bars: Special configuration of conductors which, when added to a conventional magnetic mirror, generate a "magnetic well" which stabilizes the mirror against MHD instabilities. & Ion: An atom (or molecule) which has become charged as a result of gaining or losing one or more orbiting electrons. A completely ionized atom is one stripped of all its electrons. * Ion acoustic wave: a longitudinal compression wave in the ion density of a plasma, which can occur at high electron temperatures and low frequencies, caused by a * Ion Cyclotron Emission (ICE): As ions gyrate around in a magnetic field (see also larmor radius or cyclotron radius), they radiate radio-frequency electromagnetic waves. This is known as ion cyclotron emission, and can be measured to help diagnose a plasma. * Ion Cyclotron Resonance Heating: Like Electron Cyclotron Heating, but heats ions using waves near the ion cyclotron frequency. See Electron Cyclotron Heating. * Ion diode: Device for producing and accelerating ion beams for light ion drivers for inertial confinement fusion. Ions are produced in an anode plasma, extracted as space-charge-limited ion flow, and accelerated to the cathode, composed of a confined electron swarm, by an applied electric field. Millions of amperes of current at millions of volts have been produced this way. * Ion Temperature: the temperature corresponding to the mean kinetic energy of the ions in a plasma. & Ionization: Process by which a neutral atom is converted to an ion (or one ion is converted to another of a different type), by removal or addition of electrons. & Ionization Energy: Generally refers to the amount of energy required to strip a particular electron from an atom. The first-ionization-energy is a commonly used quantity in many fields of physics and chemistry. Typically measured in electron-volts. Equivalent to the atomic binding energy of the electron. & Ionization Potential: See ionization energy. * Ionizing radiation: Any high-energy radiation which can displace electrons from atoms or molecules, thereby producing ions. Examples: alpha-particle radiation; beta radiation; x-rays, gamma, and hard ultraviolet light; and accelerated ions. Ionizing radiation in large quantities may cause severe skin and tissue damage and adverse effects. (On the other hand, but not to belittle the hazards of radiation, we are continuously exposed to a "natural background" of ionizing radiation too.) * Ionosphere: Ionized region of the upper earth atmosphere, which behaves like a plasma, including reflection of AM radio waves and generation of auroral glows. * Irradiation: Process of exposure to radiation. * Isomer, Nuclear: two nuclei with the same nuclear mass (total number of protons and neutrons) but different nuclear compostions. (e.g.: T & 3He are isomers: T has 1p, 2n; 3He has 2p, 1n) & Isotope: One of several species of the same element, possessing different numbers of neutrons but the same number of protons in their nuclei. Most elements have several stable isotopes, and also several possible unstable and semi-stable isotopes. The chemical and physical properties of the different isotopes are generally the same (except for the slight mass difference and the possibility of radioactivity). Examples include the hydrogen isotopes protium (ordinary hydrogen), deuterium, and tritium (two neutrons, one proton); also uranium 238, 233, and 235. The chemistry of an element depends only on the number of protons (nuclear charge) and is therefore the same for all isotopes of an element, but the nuclear properties of different isotopes will be different. There are roughly 300 known stable isotopes, and over 1000 unstable ones. & Isotropic: adjective which describes a medium whose physical properties are independent of the direction in which they are measured.