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Subject: Conventional Fusion FAQ Glossary Part 20/26 (T)

This article was archived around: 11 Nov 1999 12:26:23 GMT

All FAQs in Directory: fusion-faq/glossary
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Archive-name: fusion-faq/glossary/t Last-modified: 25-Feb-1995 Posting-frequency: More-or-less-quarterly Disclaimer: While this section is still evolving, it should be useful to many people, and I encourage you to distribute it to anyone who might be interested (and willing to help!!!).
=============================================================== Glossary Part 20: Terms beginning with "T" FREQUENTLY USED TERMS IN CONVENTIONAL FUSION RESEARCH AND PLASMA PHYSICS Edited by Robert F. Heeter, rfheeter@pppl.gov 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). ================================================================== TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTT # t: variable generally used to represent time # tau: label generally used to represent confinement time # T: variable generally used to represent temperature # T: nuclear/chemical symbol for tritium/triton; see entry $ T: abbreviation for Tesla, SI unit of magnetic field; see entry > TARA: See entry under TARA below. @ TCI: Two-Color Interferometry @ TCV: Variable Configuration Tokamak - from French; see Section 5. @ TCX: Tangential Charge Exchange # Te: (subscript e) Electron Temperature $ Tera: Metric prefix indicating one trillion (10^12) times base unit. $ Terawatt: One trillion (10^12) watts. @ TEXT-U: TEXas Tokamak-Upgrade; see entry under TEXT below. @ TEXTOR: Tokamak EXperiment for Technology Oriented Research; see entry for TEXTOR below. @ TF: Toroidal Field (or Toroidal Field Coil) @ TFR: FRench Tokamak, see entry under TFR below @ TFTR: Tokamak Fusion Test Reactor; see entry # Ti: Chemical Symbol for Titanium; if subscript i, Ion Temperature @ TMX: Tandem Mirror eXperiment; see entry. @ TMX-U: Tandem Mirror eXperiment-Upgrade; see entry. @ TORMAC: TORoidal MAgnetic Cusps; see entry @ TPX: Tokamak Physics Experiment; see entry @ TRANSP: Princeton's TRANSPort Simulation Code (Tokamak) @ TW: terawatt; 10^12 watts; see watt. @ TWyr: terawatt-year; Unit of energy equal to 3.15 x10^19 joules or 30 Quads (see entries) > T-3: A Soviet tokamak located at the Kurchatov Institute in Moscow which first proved concept viability, by producing a plasma temperature of 10 million degrees centigrage/Kelvin. (Result was disbelieved in the West until a British team confirmed the results using Thomson scattering.) > T-10: A later, larger Soviet tokamak, located at the Kurchatov Institute (Moscow). (PLT was largely a copy of T-10, only PLT had neutral beams, whereas T-10 was (I believe) purely ohmic-heated. > T-11: Another Soviet tokamak (rather small) located at the Kurchatov Institute (Moscow); studied neutral-beam heating. > T-15: (formerly T-10M) Another, much larger Soviet tokamak (somewhat smaller than TFTR, but similar size) with superconducting magnets, currently (?) under construction. (Was it completed? Is it operational?) > T-20: A huge Soviet tokamak that was designed to operate under reactor conditions (net energy production) but which was abandoned for budgetary reasons. > Tandem Mirror Experiment: (TMX) Located at LLNL, this was one of the first devices to experiment with placing magnetic mirror devices at either end of a (relatively) long cylindrical central region. In TMX the plasma was supplied by neutral beams. > Tandem Mirror Experiment-Upgrade: (TMX-U) Upgrade of TMX which was brought on line in 1983. Incorporated rf heating systems and improved neutral beam systems. Predecessor to MFTF-B (see entry) as a flagship magnetic mirror in the U.S. > TARA: Medium scale tandem mirror device commissioned at MIT in 1984 to develop greater understanding of basic tandem mirror physics, with emphasis on microstability properties, thermal barrier formation, and RF heating. * Target Plasma: Plasma used to trap a neutral atom beam. A background plasma of sufficiently high density and temperature can ionize neutral atoms more effectively than the Lorentz process (where v cross B creates effective electric field?). * Tau: See # tau above. ! Taylor, J.B.: Renowned plasma physicist; noted for helicity work?? * Taylor State: (John Cobb?) * Tearing Mode, Tearing Instability: A resistive MHD instability which is spatially localized near a rational surface and which grows at a rate slower than the MHD Alfven rate, but faster than the resistive skin diffusion rate. The instability "tears" magnetic field lines and reconnects them into a new state of lower magnetic energy. (see other entries for more information about the terms used above.) & Temperature, Kinetic: See Temperature, Plasma, and Kinetic Temperature. * Temperature, Plasma: A measure of the random (thermal) kinetic energy of the ions or electrons in the plasma. The temperature of each component of a plasma depends on the mean kinetic energy of that component. An example of this is the fluorescent light bulb, which is an example of a weakly-ionized plasma where the electrons are at temperatures of tens of thousands of degrees, whereas the ions and neutrals are much cooler (so that you can touch the bulb without being burned). See atomic temperature, electron temperature, and ion temperature. $ Tesla - SI unit of magnetic field strength; 1 tesla = 10,000 gauss. > TEXT-U Device: A medium-size research tokamak at the University of Texas, Austin; upgraded version of the TEXT device, with divertor. > TEXTOR: (Tokamak EXperiment for Technology Oriented Research. Medium-sized European tokamak located in Julich, Germany. Research objectives involve things like developing plasma-facing components and studying effects of plasma-wall interactions. > TFR: An iron-cored French Tokamak, now retired (I believe). Pioneered a number of important tokamak ideas and innovations. * Thermal Barrier: In magnetic mirror devices, this is a depression of electrostatic potential formed by enhancing ion loss in the region between the central cell and the positive potential plug. The thermal barrier significantly reduces the density requirements in the plug and lowers the overall power required to sustain the solenoidal plugging by thermally decoupling central cell electrons from the end plugs. & Thermal Conductivity: degree to which a substance transmits heat. (basic definition, I believe, is: (heat flow) = (thermal conductivity) * (temperature gradient) ) & Thermal Conversion Cycle: Process of generating electrical power with a fusion reactor by means of a steam / other gas turbine. This is distinct from "direct conversion" cycles. & Thermal Efficiency: Ratio of the electric power produced by a power plant to the original amount of heat produced. This measures the efficiency with which the thermal energy is converted to electricity. * Thermal (Slow) Neutron: A neutron in thermal equilibrium with its surrounding environment. Thermal neutrons are those that have been slowed down by a moderator to speeds characteristic of the local temperature. (Compare with fast neutron.) & Thermodynamic Equilibrium: There is a very general result from statistical mechanics which states that, if a system is in thermodynamic equilibrium with another (or several other) system(s), all processes by which the systems can exchange energy must be exactly balanced by their reverse processes, so that there is no net exchange of energy. For plasma systems in thermodynamic equilibrium, ionization must be balanced by recombination, Bremsstrahlung by absorption, and so on. When thermodynamic equilibrium exists, the distribution function of particle energies and excited energy levels of the atoms can be obtained from the Maxwell-Boltzmann distribution (which is a function only of the temperature). The Saha equation is a special application of this. * Thermonuclear Conditions: Achievement of an adequately confined plasma, having temperature and density sufficiently high to yield significant release of energy from fusion reactions. * Thermonuclear Fusion: fusion achieved by heating up the fuel into the plasma state to the point where ions have sufficient energy to fuse. > Theta Pinch: A fast-pulsed pinch device in which the external current imposed goes in the azimuthal/circumferential direction (generally in a solenoid) around a cylindrical plasma. Use of a fast-rising solenoidal current causes a rapidly increasing axial magnetic field, which compresses and heats the plasma. * Thomson Scattering: Scattering of photons by electrons, in the classical (low photon energy) limit. Laser light passed through a plasma will experience Thomson scattering; the spread of the scattered light in energy provides a very good measurement of the electron temperature of the plasma. > Tokamak: (Acronym created from the Russian words, "TOroidalnaya KAmera MAgnitnaya," or "Toroidal Chamber-Magnetic".) Because the tokamak is the primary research machine for magnetic confinement fusion today, we provide several descriptions from various sources: -> One of several types of toroidal discharge chamber in which a longitudinal magnetic field is used to confine a plasma. The tokamak is distinguished by a plasma current running around the torus, which generates a stabilizing poloidal magnetic field. An externally-applied vertical magnetic field is also used to achieve plasma equilibrium. -> (Contributed by James Crotinger, jac@gandalf.llnl.gov) An axisymmetric toroidal confinement device characterized by a strong toroidal magnetic field (1-10 Tesla) and a toroidal plasma current (several mega-Amps) that leads to a modest poloidal magnetic field. The plasma current is usually induced by ramping a current in a large solonoid along the symmetry axis of the tokamak. This is an inherently pulsed mode of operation, and other mechanisms of current drive are under investigation. -> TOKAMAK (tokomak) (contributed by Paul M. Koloc) "A three component magnetoplasma toroidal construct in which the poloidal magnetic component is provided by a toroidal plasma current. The other two components are coil driven, namely, the vertical field (which opposes the major radial expansion) and the toroidal field (which acts to provide a "stiff guide" field for the plasma to gain more MHD stability. Note: It is better to think that the toroidal or longitudinal field "stiffens" the plasma as against flopping or kinking, while the plasma current driven poloidal (locally azimuthal) field provides "confinement" pressure. Actually, the toroidal field interacting with plasma diamagnetism may also contribute to a "magnetic bouyancy", which is a sort of UN-confinement -- (it actually gives the plasma a tendency to expand radially outward in the equatorial plane)." -> (from Herman:) "Based on an original Soviet design, a device for containing plasma inside a torus chamber by using the combination of two magnetic fields - one created by electric coils around the torus, the other created by intense electric current in the plasma itself, which also servers to heat the plasma [partially]. TFTR and JET are tokamaks." > Tokamak Fusion Test Reactor: Large tokamak at Princeton, first machine to use 50-50 mix of D-T fuel, current world's record holder in fusion energy production. Largest tokamak in the United States. > Tokamak Physics Experiment: Smaller successor to TFTR at Princeton. Engineering design underway; construction scheduled to begin in FY 1995. > Tore Supra: Large tokamak in Cadarache (southern France). The second largest tokamak in Europe; largest tokamak using superconducting toroidal field magnets. Tore Supra has a circular cross-section (like TFTR), which limits the achievable confinement time and experimental flexibility. In addition to developing superconducting technology, it concentrates on the physics of long pulses and ergodic magnetic limiters. See also: ergodic; magnetic limiter; superconductor; tokamak. * Toroidal: in the shape of a torus, or doughnut. Or: Coordinate indicating which part of the torus a particle is in. (Azimuthal coordinate) Or: General term referring to toruses as opposed to other geometries. (e.g., tokamaks and stellarators are examples of toroidal devices.) * Toroidal Field Coils: Coils in a toroidal system, typically wound around the torus in a solenoid-like arrangement, used to generate the toroidal magnetic field. Each turn completely surrounds the plasma. > TORMAC: (TORoidal MAgnetic Cusps) Hybrid confinement scheme operating at high beta. A region of closed toroidal magnetic flux with high-beta plasma is separated by a narrow sheath from the surrounding field, which contains externally produced poloidal components arranged in a toroidal line-cusp configuration. Plasma migrating to the outer sheath is temporarily mirror-confined before being removed in a divertor system. > Toroidal Pinch: & Torque: > Torsatron: A modification of the stellarator concept, the torsatron has a toroidal non-axisymmetric configuration, and rotational transform is provided by external coils. Unlike a stellarator, however, both toroidal and poloidal fields are generated by helical fields alone, with half the number of helical conductors required for a stellarator. & Transformer, Transformer Effect: See entry for Induction. & Transmittance: Ratio of the radiant power transmitted by an object to the incident radiant power. See also reflectivity. & Transmutation: Transformation of atoms of one element into atoms of another element via nuclear reactions. (e.g., the transmutation of uranium-238 into plutonium-239 via the absorption of a neutron and subsequent beta emission.) * Transport: Refers to processes which cause heat energy, or particles, or something else, to flow out of the plasma and cease being confined. Diffusion partly determines the rate of transport. See also: diffusion, classical diffusion, neoclassical diffusion, anomalous diffusion. * Transverse Waves: Waves in which the direction of the oscillation is perpendicular ("transverse") to the direction of the wave propagation. Examples include plucked strings and electromagnetic waves in free space/air. * Trapped-Particle Instability: Slowly-growing class of instabilities driven by particles which cannot circulate freely in a toroidal system. See also banana orbit. * Trapped-Particle Modes: See trapped-particle instability * Triangularity: Geometric factor measuring an aspect of the shape (how "triangular" it is) of the cross-section of a non-circular plasma in a toroidal device. See also elongation. & Tritium: A radioactive isotope of hydrogen with one proton and two neutrons in its nucleus and one orbiting electron. A more efficient fuel than ordinary hydrogen (protium) because of the extra neutrons. Tritium decays to helium-3 by emission of an electron ("beta emission") with a half-life of 12.3 years. Tritium can be synthesized from deuterium via neutron bombardment, or by fissioning lithium (see lithium). * Tritium-Breeding Ratio: The amount of tritium generated by the breeding blanket of a D-T fusion reactor, divided by the amount of tritium burned in the reactor. A tritium breeding ration greater than unity is necessary for self-sufficient fueling. * Triton: nucleus of a tritium atom; tritium ion. * Troyon Limit: see beta limit * Turbulence: "Violent macroscopic fluctuations which can develop under certain conditions in fluids and plasmas and which usually result in the rapid transfer of energy through the medium." (PPPL & OSTI Glossaries have same entry) * Turbulent Heating: Technique of using turbulence induced by large electric fields to rapidly heat a plasma. * Two-Stream Instability: Instability which can develop when a stream of particles of one type has a velocity distribution with its peak well separated from that of another type of particle through which it is flowing. A stream of energetic electrons passing through a cold plasma can, for example, excite ion waves which will grow rapidly in magnitude at the expense of the kinetic energy of the electrons.