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=============================================================== Glossary Part 6: Terms beginning with "F" 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). ================================================================== FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF # F: Variable typically used for force; sometimes flux. & F: Chemical symbol for the element fluorine. * FLiBe or flibe or FLIBE: Fluorine-LIthium-BEryllium; see entry "Flibe" below. @ FEDC: Fusion Engineering Design Center; see entry @ FLR: Finite Larmor Radius; see entry @ FPD: Fusion Power Demonstration facility; see DEMO. @ FRC: Field-Reversed Configuration; see entry @ FY: Fiscal Year; see entry & Fabry-Perot Interferometer: A type of interferometer with two parallel mirrors (with a variable separation of a few centimeters) arranged so that incoming light is reflected between them multiple times before ultimately being transmitted. Useful in spectroscopy because it gives very good frequency resolution without losing too much of the incident signal. * Faraday Rotator: A device which rotates the plane of polarization of an optical-light pulse, typically by using a glass disc suitably doped with a magnetic ion and placed in a magnetic field. These devices are used to isolate (protect) a laser amplifier chain against back-reflection from the laser target; the Faraday rotator in this case gives a 90-degree phase change on the round trip, so that the returning light is rejected by a polarizer which transmits the outgoing light. * Fast neutron: Neutron with energy greater than roughly 100,000 electron volts (100 keV). Distinguished from slow or thermal neutrons. (See appropriation entries.) * Fertile Material: In nuclear physics, this refers to a nuclide which converts to fissile material (see entry) upon neutron capture and subsequent radioactive decay. Examples include Uranium-238 and Thorium-232. & Field: In physics, any macroscopic quantity which exists (and typically varies) througout a region of space. Standard examples include Electric and Magnetic fields, velocity flow fields, gravitational fields, etc. & Field Lines: Lines in space along which a field is either changing or not changing (depends on the field) but which help to create diagrams which characterize the behavior and effects of the field. For instance, electric field lines run in the direction that the electric field will push charged particles; the strength of the field is proportional to the density of the field lines. On the other hand, the magnetic force pushes particles in a direction perpendicular to both the particle's velocity and the direction of the magnetic field line. > Field-Reversed Configuration: A compact torus produced in a theta pinch and having (in principle) no toroidal field. The potential advantages for a fusion reactor include a simple (linear) machine geometry, an average plasma pressure close to the confining field pressure, and physical separation of formation and burn chambers. The are predicted to be violently unstable to tilting, but this is rarely observed. See also: compact torus, theta pinch. (Arthur Carlson, email@example.com) * Field Shaping Coils: Type of poloidal field coils (in a tokamak) which create magnetic fields which shape and control the plasma. Used to constrain horizontal and vertical displacements of the plasma, as well as (in some configurations) produce non-circular plasma cross sections (poloidal cross-section) and/or create one or more divertor separatrices. (See relevant entries.) * Finite Larmor Radius: In many plasma theories the size of the Larmor radius (or gyroradius - see entries) is assumed to be negligibly small, or infinitesimal. Different effects occur when the size of the Larmor radius is finite and needs to be considered. (Anyone out there with a succint, but more detailed explanation?) * First Wall: The first physical boundary that surrounds a plasma. * Fiscal Year (FY): Year used to open and close accounting records; not necessarily the same as the calendar year. (For instance, the U.S. government's Fiscal Year begins Oct 1 and ends Sept 30.) * Fishbones: Oscillations in soft x-ray emissions which occur during intense neutral-beam heating; associated with a recurring m=1 internal kink mode. Mode was given its name from its characteristic signal (looked like the bones of a fish, of course). Fishbones are associated with loss of fast ions from the plasma and are triggered by exceeding the upper limit on plasma beta. (see relevant entries) * Fissile Material: Material containing a large number of easily fissionable nuclei which give off multiple neutrons in the fission process. Usual meaning is that if a sufficiently large amount of fissile material is put together, a fission chain reaction can occur. Sometimes used synonymously with "fissionable material," i.e., material that *can* be fissioned (though often under restricted circumstances, such as only with thermal (slow) neutrons). A more restricted meaning use of fissile material limits the concept to those materials which can be fissioned by neutrons of all energies (fast & slow). Examples include Uranium-235 and Plutonium-239. & Fission (Nuclear): Nuclear decay process whereby a large nucleus splits into two smaller (typically comparably-sized) nuclei (which are thus nuclei of lighter elements), with or without emission of other particles such as neutrons. When it occurs, fission typically results in a large energy release. Fission can occur spontaneously in some nuclei, but is usually caused by nuclear absorption of gamma rays, neutrons, or other particles. See also spallation, radioactivity. * Fission Bomb: see atomic bomb, A-bomb. * Fission Reactor: (from Herman) A device that can initiate and control a self-sustaining series of nuclear fissions. * Flat-top: Stable period in the middle of a tokamak discharge, characterized by a flat, stable peak in a plot of plasma (current, temperature) vs. time. * Flibe: Molten salt of Fluorine, Lithium, and Beryllium; candidate blanket/coolant/breeder material for fusion reactors. * Flute Instability: Term used to describe an interchange instability in which the perturbation is uniform parallel to the magnetic field. In cyclindrical geometry, the structure resembles a fluted column (as in classical architecture). Occurs in some mirror machines. & Flux: The total amount of a quantity passing through a given surface per unit time. Typical "quantities" include field lines, particles, heat, energy, mass of fluid, etc. Common usage in plasma physics is for "flux" by itself to mean "magnetic field flux." & Flux Density: Total amount of a quantity passing through a unit surface area in unit time. See also flux, above. * Flux freezing: See frozen-in law. * Flux surfaces: See magnetic flux surfaces. * Flux trapping: See frozen-in law. & F-number: In optics, denotes the ratio of the equivalent focal length of an objective lens to the diameter of its entrance pupil. * Fokker-Planck Equation: An equation that describes the time rate of change of a particle's velocity as a result of small-angle collisional deflections. Applicable when the cumulative effect of many small-angle collisions is greater than the effect of rarer large-angle deflections. & Force: Rate of change of momentum with time. Forces are said to cause accelerations via F = ma (Newton's law). There are four primary forces known presently: the gravitational, electromagnetic, weak nuclear, and strong nuclear forces. The gravitational and electromagnetic forces are long-range (dropping as 1/distance^2), while the nuclear forces are short range (effective only within nuclei; distances on the order of 10^-15 meters). The electromagnetic force is much stronger than the gravitational force, but is generally cancelled over large distances because of the balance of positive and negative charges. Refer to entries for each force for more information. See also momentum. * Free Electron: An electron not bound to an atom, molecule, or other particle via electric forces. * Free Wave: A wave (e.g., electromagnetic) travelling in a homogeneous infinite medium (no boundary conditions). * Frozen-in Flow Law: In a perfect conductor, the total magnetic flux through any surface is a constant. In a plasma which is nearly perfectly conducting, the relevant surfaces move with the plasma; the result is that the plasma is tied to the magnetic field, and the field is tied to the plasma. Motion of the plasma thus deforms the magnetic field, and vice versa. * Fusion (Nuclear): a nuclear reaction in which light atomic nuclei combine to form heavier nuclei, typically accompanied by the release of energy. (See also Controlled Thermonuclear Fusion) % Fusion Engineering Design Center: Facility managed by ORNL and staffed mainly by industrial personnel; undertakes detailed engineering design of planned fusion facilities. (Is it still in operation? The reference I have is out of date.) * Fusion Reactor: Device which creates energy in a controlled manner through fusion reactions. > Fusion-Fission Hybrid: Proposed nuclear reactor relying on both fusion and fission reactions. A central fusion chamber would produce neutrons to provoke fission in a surrounding blanket of fissionable material. The neutron source could also be used to convert other materials into additional fissile fuels (breeder hybrid). Safer than a plain fission reactor because the fission fuel relies on the fusion neutrons, and therefore won't spontaneously melt down. On the other hand, hybrids are more complex because of the fusion power core, and still generate fission's radioactive byproducts. But could be more economical and have easier technical requirements than a straight fusion reactor.