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=============================================================== Glossary Part 5: Terms beginning with "E" 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). ================================================================== EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE # e: symbol for the electron, for the unit electric charge (e = 1.6x10^-19 coulombs), and for a Euler's fundamental mathematical constant e = 2.71828... # E: Variable typically used for Energy or Electric Field (usually in vector notation in the latter case; which is meant is usually clear from context; when both are used in the same place the energy is usually represented as U instead of E.) @ EBT: Elmo Bumpy Torus; see entry @ EC: European Community; see entry @ ECDC: Electron Cyclotron Discharge Cleaning; see entry @ ECE: Electron Cyclotron Emission; see entry @ ECH: Electron Cyclotron Heating; see entry @ ECRH: Electron Cyclotron Resonance Heating - same as ECH. @ EF: Equilibrium (vertical) Field Electromagnet Coil; see vertical field $ ECU: European Currency Unit @ ELM: Edge-Localized Mode; see entry @ EM: Electromagnetic @ EM Wave: Electromagnetic Wave; see entry @ EPA: Environmental Protection Agency (U.S.); see entry @ ERDA: Energy Research and Development Agency; see entry @ ESECOM: Reactor design study done in the mid 1980s to evaluate the Environmental, Safety, and ECOnoMic potential of different types of fusion and advanced fission reactors. @ ESNET: Energy Sciences NETwork; no entry yet @ ETF: Engineering Test Facility @ EU: European Union; see entry @ eV: Electron-volt; see entry $ Exa: metric prefix for 10^18 or 1,000,000,000,000,000,000 $ Exajoule: unit of energy, 10^18 joules; often used as unit of measure for world annual energy use. Comparable in size to a Quad (1 EJ = 0.948 Quads); see entry for Quad. * E-Coil: The plasma current driving (Ohmic Heating) coil in a Doublet device (see entry for doublet). Ideally the E-coil makes no magnetic field in the confinement system. (?) * E-Layer: Cylinder of relativistic electrons gyrating in a magnetic field, which produce a self-field strong enough to dominate the externally applied field and produce a field-reversal (where the B field changes sign) in the system. See Field-Reversed Configuration, Field-Reversed Pinch. * Echoes: Wave packets (pulses) which have been reflected or otherwise returned to the detector, which are sufficiently delayed and retain sufficient magnitude so that they are perceived as a signal distinct from the one transmitted directly. (In other words, just like sound echoes, only for analogous phenomena with other waves.) * Eddy Current: Electric current induced inside a conductor when the conductor (a) moves through a nonuniform magnetic field, or (b) experiences a change in the magnetic flux through its surface. * Eddy-Current Loss: Energy loss due to eddy currents circulating in a resistive material. * Edge Localized Mode: (ELM) Mode found often in H-mode plasmas. This is a temporary relaxation of the very high edge gradients found in H-modes. It may be a relaxation back to the L-mode. (Borrowed from a posting by Paul Stek) * Edge Plasma: Cooler, less dense plasma away from the center of a reactor; affected by limiter or divertor, includes scrape-off layer. Distinguished from core plasma. See entries for relevant terms used. * Edge-Localized Mode: (info from Paul Stek) Found often in H-mode plasmas, this is a temporary relaxation of the very high edge gradients found in H-modes. It may be a relaxation back to the L-mode. * Effective Collision Cross-section: (See collision cross section) * Effective Collision Radius: Effective size of a particle equal to the square root of (cross section/pi). Determines the effective range of interaction of the particle. * Effective Half-Life: Time required for a radioactive substance contained in a biological system (such as a person or an animal) to reduce its radioactivity by half, as a combination result of radioactive decay and biological elimination from the system. & Eigenfrequency: One of the characteristic frequencies at which an oscillatory system can vibrate. & Eigenfunction: Function describing an eigenstate of a system. & Eigenstate: One of the characteristic states of an oscillatory system, such that the system does not leave the state unless disturbed. (?) & Eigenvector: Same thing as an eigenfunction, only from the perspective that the eigenfunction is a "vector" in an appropriate mathematical vectorspace. * Eikonal Equation: An equation for propagation of electromagnetic or acoustic waves in an inhomogenous medium; valid only when the scale length for variation in the properties of the medium is small compared to a wavelength. (Similar in character to WKB?) & Elastic: Term used to describe a process in which kinetic energy is conserved; usually refers to (elastic) collisions or (elastic) scattering. & Electric Charge: See charge, electrical. & Electric Field: A property of a patch of space which causes the acceleration of electric charges located at that patch of space. The acceleration is given by a = qE/m, where q is the charge, E the electric field vector, and m the mass of the particle. % Electric Power Research Institute: (EPRI) Research organization funded by the electric power utilities to study, well, electric power. * Electric Probe: See Langmuir Probe. & Electrical Conductivity: Degree to which a substance conducts electric current. Can be defined by: (current density) = (conductivity) * (applied electric field) Electrons and ions both contribute to current in proportion to their mobility in the system. In a plasma with a magnetic field, there is no longer a one-to-one correspondence between current and electric field. Instead, the current in each direction can be due to combinations of the electric fields in all the other directions. In this case, the current density and the electric field are vectors, and the conductivity becomes a tensor (matrix) which relates them. * Electromagnetic Coupling: A means of extracting energy from a magnetically confined plasma, where the plasma expands and pushes on the confining magnetic field, causing electrical energy to be generated in the external field-generating circuits. & Electromagnetic Force: * Electromagnetic Radiation: Radiation (such as radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, and gamma rays) which consists of associated, interacting electric and magnetic field waves which travel at the speed of light (because electromagnetic radiation *is* light, except for the variation in frequencies!). All forms of electromagnetic radiation can be transmitted through vacuum. Electromagnetic waves in plasmas are generally more complex in their behavior, depending on their frequency. & Electromagnetic Wave: Wave characterized by combined oscillations of both electric and magnetic fields. The particle equivalent is the photon. There is a whole spectrum of electromagnetic waves where the classes are distinguished by energy (or, equivalently, wavelength or frequency); the spectrum of electromagnetic waves includes radio waves, microwaves, infrared light, visible light, ultraviolet light, x-rays, and gamma rays. & Electron: Elementary particle with a negative electric charge. Electrons orbit around the positively charged nucleus in an atom. The charge on an electron is -1.6x10^-19 coulombs; the electron has a mass of 9.11 x 10^-31 kg (about 1/1837 times that of a proton.) The configuration of electrons around an atom determines its chemical properties. The positron is the antiparticle to the electron, and is identical except for having a positive charge. > Electron Beam Fusion Accelerator: See PBFA (Particle Beam Fusion Accelerator) * Electron Capture: Nuclear decay process whereby a proton in the nucleus absorbs an orbiting electron and converts to a neutron. * Electron Cyclotron Discharge Cleaning: (ECDC) Using relatively low power microwaves (at the electron cyclotron frequency) to create a weakly ionized, essentially unconfined hydrogen plasma in the vacuum chamber. The ions react with impurities on the walls of the tokamak and help remove them from the chamber. For instance, Alcator C-mod typically applies ECDC for a few days prior to beginning a campaign, and a few hours before each day's run. * Electron Cyclotron Emission: (ECE) As electrons gyrate around in a magnetic field (see also larmor radius or cyclotron radius), they radiate radio-frequency electromagnetic waves. This is known as electron cyclotron emission, and can be measured to help diagnose a plasma. * Electron Cyclotron Heating: (ECH or ECRH) Radiofrequency (RF) heating scheme that works by injecting electromagnetic (EM) wave energy at the electron cyclotron gyration frequency. The electric field of the EM wave at this frequency looks to a gyrating electron like a static electric field, and it causes acceleration of the electron. The accelerated electron gains energy, which is then shared with other particles through collisions, resulting in heating. * Electron Cyclotron Wave: Radiofrequency waves at the electron cyclotron frequency. See also Whistler. * Electron Density: Number of electrons in a unit volume. See density for more info. * Electron Temperature: The temperature corresponding to the mean kinetic energy of the free electrons in a plasma. $ Electron-volt: 1 eV = 1.6 x 10^-12 erg, or 1.6 x 10^-19 Joules. This is a unit of kinetic energy equal to that of an electron having a velocity of 5.93 x 10^5 m/sec. This is the energy an electron (or other particle of charge=1 such as a proton), gains as it is accelerated through a potential difference of 1 volt. In plasma physics the eV is used as a unit of temperature; when the mean particle energy is 1eV, the temperature of the plasma is roughly 11,700 Kelvin. * Electrostatic Analyzer: A device which filters an electrn beam (band-pass), permitting only electrons within a narrow energy (velocity) range to pass. > Electrostatic Confinement: An approach to fusion based on confining charged particles by means of electric fields, rather than the magnetic fields used in magnetic confinement. See discussion in Section 4 for more information. * Electrostatic Waves: Longitudinal oscillations appearing in a plasma due to a perturbation of electric neutrality. For a cold unmagnetized plasma, or at large wavelengths, the frequency of these waves is by definition the plasma frequency. & Element: One of the fundamental chemical substances which cannot be divided into simpler substances by chemical means. Atoms with the same atomic number (# of protons) all belong to the same element. (e.g., hydrogen, helium, oxygen, lead) (list and perhaps periodic table in appendix? isotope table with half-lives and decay modes might also be useful.) & Elementary Particles worth knowing about: (at the nuclear-energy level) electron & positron - seem to be stable proton - thought to be stable, life > 10^30 sec neutron - decays in ?10 min unless it's in a nucleus, which often extends its life. other particles important for nuclear energy: muon, neutrino (m,e,tau), photon muonic atoms pi-meson antiparticles this part is new - maybe separate entries with listing here?? > Elmo Bumpy Torus: Bumpy Torus at ORNL; no longer operating. See Bumpy Torus, ORNL. * Elongation: parameter indicating the degree to which the cross section of a toroidal plasma is non-circular. kappa=b/a, where "b" and "a" are the vertical and horizontal minor radii. As kappa is increased, the confinement in relation to the total current improves, but the plasma also becomes more and more unstable to vertical displacements. A circular plasma has kappa of 1, a common value for elongated plasmas is 1.7, and the absolute limit is probably around 2. & Energy: Typically defined as "the ability to do work". Power is the rate at which work is done, or the rate at which energy is changed. "Work" characterizes the degree to which the properties of a substance are transformed. Energy exists in many forms, which can be converted from one to another in various ways. Examples include: gravitational energy, electrical energy, magnetic and electric field energy, atomic binding energy (a form of electrical energy really), nuclear binding energy, chemical energy (another form of electrical energy), kinetic energy (energy due to motion), thermal energy ("heat"; a form of kinetic energy where the motion is due to thermal vibrations/motions), and so on. * Energy Balance: Comparison of energy put into a plasma with the energy dissipated by the system; related to energy confinement. * Energy Confinement Time: See energy loss time. * Energy Loss Time: Characteristic time in which 1/e (or sometimes 1/2) of a system's energy is lost to its surroundings. In a plasma device, the energy loss time (or the energy confinement time) is one of three critical parameters determining whether enough fusion will occur. (See Lawson criterion) * Energy Replacement Time: Time required for a plasma to lose (via radiation or other loss mechanisms) an amount of energy equal to its average kinetic energy. % Energy Research and Development Agency (ERDA): US Agency created by splitting of the AEC into ERDA and NRC in about 1975, charged with managing US energy R&D (???). Merged with ??? to become the Department of Energy in about 1977. (???? correct? help??) * Entropy Trapping: The process of trapping an ordered beam of particles in a magnetic field configuration (e.g., cusp geometry) by randomizing the ordered motion of the particles, with corresponding increase in the entropy of the system. % Environmental Protection Agency: Agency within the executive branch of the U.S. government (under the Department of the Interior? Independent?) charged with, well, protection of the environment. Activities include research, regulatory, and cleanup functions. (Any government people reading this who could help me out?) * Equations of Motion: Set of equations describing the time evolution of the variables which describe the state of a physical system. * Equilibrium: [ acknowledgements to John Cobb ] An equilibrium is a state of a system where the critical parameters do not change significantly, within a given time frame. In the case when this time frame is infinite, It is called a Thermodynamic equilibrium. There are many cases where a plasma equilibrium is constant on some fast time scale, but changes over some slower time scale. For example, an IDEAL MHD equilibrium is constant over fluid time scales (microseconds to milliseconds), but it will evolve on the slower resistive or viscous time scales (milliseconds to seconds). All terrestial plasmas are NOT in thermodynamic equilibrium, but they may be constant over very long time periods. An equilibrium is unstable when a small change in a critical parameter leads the state of the system to diverge from the equilibrium. An equilibrium is stable when a small change in a critical parameter leads to a "restoring force" which tends to return the system to equilibrium. * Equilibrium Field: See Vertical Field $ Erg / ergs: CGS unit for energy. 1E7 ergs = 1 joule. * Ergodic: A mathematical term meaning "space-filling". If a magnetic field is ergodic, any field line will eventually pass arbitrarily close to any point in space. Closely related to "chaotic". * Ergodic Regime: In this regime, a given magnetic field line will cover every single point on a magnetic surface (see magnetic surface or flux surface) if the rotational transform (or q) is not rational. * ESECOM: Reactor design study done in the mid 1980s to evaluate the Environmental, Safety, and ECOnoMic potential of different types of fusion and advanced fission reactors. * Eulerian Coordinates: Coordinates which are fixed in an inertial reference frame. % European Community: see European Union % European Union: (from Herman) Organization of European countries (formerly European Community, EC, formerly European Economic Community, EEC) established in 1967 to coordinate policies on the economy, energy, agriculture, and other matters. The original member countries were France, Belgium, West Germany, Italy, Luxembourg, and the Netherlands. Joining later were Denmark, Ireland, the United Kingdom, Greece, Spain, and Portugal. Other countries are in the process of joining now. % Euratom: European Atomic Energy Community. International organization established in 1958 by members of the European Economic Community for the purpose of providing joint funding and management of the scientific research of the member countries - initially Belgium, France, Italy, Holland, and West Germany. * Excitation Radiation: Line radiation (at characteristic frequencies / wavelengths) as a result of the excitation of excited states, and the subsequent de-excitation of these states by radiative transitions.