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- Path: senator-bedfellow.mit.edu!faqserv
- From: Robert F. Heeter <rfheeter@princeton.edu>
- Newsgroups: sci.physics.fusion,sci.answers,news.answers
- Subject: Conventional Fusion FAQ Glossary Part 12/26 (L)
- Supersedes: <fusion-faq/glossary/l_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:25:42 GMT
- Organization: Princeton University
- Lines: 346
- Approved: news-answers-request@MIT.EDU
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/l_942323057@rtfm.mit.edu>
- References: <fusion-faq/glossary/intro_942323057@rtfm.mit.edu>
- Reply-To: rfheeter@pppl.gov
- NNTP-Posting-Host: penguin-lust.mit.edu
- Summary: Fusion energy represents a promising alternative to
- fossil fuels and nuclear fission for world energy
- production. This Glossary is a compendium of Frequently Used
- Terms in Plasma Physics and Fusion Energy Research. Refer
- to the FAQ on Conventional Fusion for more detailed info
- about topics in fusion research. This Glossary does NOT
- discuss unconventional forms of fusion (like Cold Fusion).
- X-Last-Updated: 1995/02/20
- Originator: faqserv@penguin-lust.MIT.EDU
- Xref: senator-bedfellow.mit.edu sci.physics.fusion:44260 sci.answers:10857 news.answers:170843
-
- Archive-name: fusion-faq/glossary/l
- Last-modified: 20-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 12: Terms beginning with "L"
-
- 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).
- ==================================================================
-
- LLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLLL
-
- # L: variable typically used to indicate self-inductance;
- see inductance.
-
- # Li: chemical symbol for the element lithium; see entry.
-
- @ L-mode: see low mode.
-
- @ LAMPF: Los Alamos Meson Physics Facility; see entry
-
- @ LANL: Los Alamos National Laboratory; see entry
-
- @ Laser: Light Amplification by Stimulated Emission of Radiation.
- see entry.
-
- @ LBL: Lawrence Berkeley Laboratory; see entry
-
- @ LCFS: Last Closed Flux Surface; see entry
-
- @ LLE: Laboratory for Laser Energetics; see entry
-
- @ LLNL: Lawrence Livermore National Laboratory; see entry
-
- @ LMFBR: Liquid-Metal Fast-Breeder Reactor; see entry
-
- @ LMR: Liquid-Metal Reactor; see entry
-
- @ LN2: Liquid (diatomic) Nitrogen (N2)
-
- @ LOCA: Loss-of-Coolant Accident; see entry
-
- @ LWR: Light-Water Reactor; see entry
-
- % Laboratory for Laser Energetics: Second-largest (?) inertial
- confinement research facility in the United States; located at
- the University of Rochester in New York state. Home of Omega;
- future home of Improved-Omega.
-
- & Lagrangian: The difference between the kinetic energy and the
- potential energy of a system of particles, expressed as a
- function of generalized coordinates and velocities. Equations
- of motion can be derived from the Lagrangian. (see an intermediate
- or advanced mechanics text for more information.)
-
- * Lagrangian coordinates: coordinates which follow fluid motion.
- (As distinct from Eulerian coordinates; see entry).
-
- * Landau Damping: Damping of a wave propagating in a hot plasma,
- due to the interaction of the wave with particles whose velocity
- is close to the phase velocity of the wave. Depends on the shape
- of the velocity-space distribution function at the phase velocity
- of the wave. More info from John Cobb, with modifications:
-
- The phenomenon is very similar to surfing on water waves at the
- beach. If a particle's speed is just slightly lower than the wave,
- then the particle can "catch the wave" and surf along at the wave
- speed. In so doing, the particle will gain some energy, which will
- be at the expense of the wave. This is called Landau Damping, since
- the loss of energy tends to damp the wave. At the same time, if a
- particle moves just slightly faster than the wave, then it will also
- be caught on the wave. However, in this case, it will slow down,
- giving the wave some extra energy. In this case particles transfer
- energy to the wave; this is called inverse Landau damping. Which
- effect dominates depends on whether there are more particles moving
- faster than the wave or more particles moving slower. Thus it
- depends on the derivative of the distribution function with respect
- to velocity, evaluated at the wave's phase velocity. Landau dmaping
- can lead to the decay of waves. Inverse Landau damping can be a
- mechanism for some kinetic instabilities.
-
- ! Langmuir, Irving (1881-1957): American chemist, won Nobel Prize in
- chemistry in 1932, developed the theory of Langmuir probes (see
- entry). Numerous inventions for General Electric (lighting).
-
- * Langmuir frequency: See plasma frequency.
-
- * Langmuir oscillation: See electrostatic waves.
-
- * Langmuir probe: a small conductive electrode used to measure the
- density, temperature, and electric potential (voltage) of a plasma.
- Plasma parameters are deduced from the probe's "Characteristic"
- current-drawn vs. voltage-applied curve.
-
- & Larmor radius: the radius of the path of a charged particle
- moving in a magnetic field (and transverse to the field lines).
- Also known as gyroradius and cyclotron radius.
-
- & Laser: An optical device that amplifies and concentrates light
- waves, emitting them in a narrow, intense beam. Laser light
- radiation is notable for its brightness and to some extent
- for its monochromaticity and spatial and temporal coherence.
-
- > Laser Fusion: Form of inertial confinement fusion where
- laser beams are used to compress and heat the fuel pellet.
-
- * Laser interferometer: an interferometer which uses a laser
- as a light source (see entries). Because of the monochromatic
- nature and high brightness of laser light, laser interferometers
- can operate with much longer beam paths and path differences
- than conventional interferometers.
-
- * Laser scattering device: See Thomson scattering device.
-
- * Last Closed Flux Surface (LCFS): [from Art Carlson] The boundary
- between the interior region of a tokamak (or other device), where the
- field lines close back on themselves, and the scrape-off layer (see
- entry), where the run into a material wall. (See also separatrix.)
-
- % Lawrence Berkeley Laboratory: Located in Berkeley, CA; Another
- large U.S. science laboratory; minor (?) U.S. fusion research center.
-
- % Lawrence Livermore National Laboratory: Located in Livermore, CA,
- about an hour east of SF in the Bay Area. Home of the Nova laser
- inertial confinement fusion program; Nova is the largest
- laser in the world. Home of the former mirror projects MFTF
- (Mirror Fusion Test Facility, shut down on the day it became
- operational, or thereabouts, due to budget cutting),
- TMX-U (Tandem Mirror eXperiment Upgrade), and the recently
- shut down Microwave Tokamak eXperiment (MTX). Some notable
- older fusion experiments at Livermore included Table Top, Toy Top,
- Baseball (and Baseball-II) and TMX (predecessor to TMX-U).
- Livermore is also the site of the Rotating Target Neutron Sources
- (I and II) for testing materials samples in high-intensity 14 MeV
- neutron fluxes and the High Field Test Stand for testing neutral
- beams. Workplace of Albert Chou and several other
- sci.physics.fusion participants. :)
-
- * Lawson Criterion: Scientific breakeven criterion based on the
- product of energy confinement time and particle density. Together
- with plasma temperature, the Lawson value of a plasma indicates
- how close it is to self-sustained (ignited) fusion; see also
- ignition.
-
- & Lenz's Law: Electromagnetism law which states that whenever
- there is an induced electromotive force (emf) in a conductor,
- it is always in such a direction that the current it would induce
- would act in opposition to the change which caused the
- induced emf.
-
- > Levitron: Single-ring multipole device with an additional
- current-carrying rod perpendicular to the ring axis.
-
- * Light-ion fusion: Light-Ion-Beam-Driven Inertial Confinement
- fusion, using beams of light ions driven at implosion targets.
- Pulsed-power driven accelerators are relatively efficient and
- cost-effective, but beam-focusing is a technical hurdle for
- this approach.
-
- > Light-Water Reactor: Class of fission reactors using ordinary
- "light" water as a coolant, rather than liquid metal or heavy
- water (water with deuterium instead of hydrogen).
-
- * Limiters: Structures placed in contact with the edge of
- a confined plasma which are used to define the shape of
- the outermost magnetic surface. See also: divertor.
-
- * Line-tying: Connection of field lines from the end of
- an open-ended device (such as a mirror system) to a conducting
- plate. The rigidity of field lines trapped in the plate can
- be transferred to the high-field region of the mirror by using
- a cold, moderately-dense plasma in between. Line-tying helps
- to stabilize against interchange instabilities (see entry).
-
- * Liquid Metal: Metal which has been heated past its melting point
- and can be used as a working fluid for pumping heat out from a
- powerplant. Liquid metal used as coolant in a system where
- significant magnetic fields exist, it behaves differently due
- to MHD effects; these cause pressure which resists fluid
- circulation, suppression of turbulence, and altered flow
- patterns compared to non-magnetic liquid metal systems.
-
- > Liquid-Metal Reactor: (Fission) reactor which uses liquid metal
- as the reactor coolant.
-
- > Liquid-Metal Fast-Breeder Reactor: (LMFBR) Fission breeder
- reactor concept (see entry for breeder reactor) using
- liquid-metal coolant and breeding additional fuel off fast
- neutrons.
-
- & Lithium: (Li) Third element in the periodic table, so all isotopes
- contain 3 protons. Pure lithium at room temperature is a soft
- silver-white material, the lightest of all metals. It is
- chemically very reactive, making it hazardous. Lithium liquefies at
- 355 degrees Fahrenheit, making it viable as a liquid-metal
- coolant. Lithium nuclei have two stable isotopes:
- Li-6 (7.5% abundance) and Li-7 (92.5%). Lithium is a candidate
- for breeding tritium (for D-T fusion) from neutrons, via the
- reactions:
-
- n + 6Li -> 4He + T + 4.8 MeV
- n + 7Li -> 4He + T + n - 2.5 MeV.
-
- * Longitudinal Waves: (by John Cobb, with editing) Waves where the
- variation of the field is partially or totally in the direction of
- propagation (parallel to wavennumber, k [a vector]). Examples
- include sound waves and Langmuir waves. Contrasted with transverse
- waves, where the variation is perpendicular to the direction of
- propagation, such as light waves.
-
- * Lorentz dissociation: dissociation of molecular ions by Lorentz
- ionization (see entry).
-
- & Lorentz Force: Total electromagnetic force on a charged particle
- moving in electric & magnetic fields. F = q(E + (v/c)xB). See
- also force, cross product, charge, velocity, and relevant
- variable symbols.
-
- * Lorentz Gas: Plasma model in which the electrons are assumed
- not to interact with each other, but only with ions (Z -> infinity)
- and where the ions are assumed to remain at rest/fixed (M-i ->
- infinity). Also known as "electron gas."
-
- * Lorentz ionization: Ionization of neutral atoms (taken generally
- at a highly-excited state) obtained by launching them at high
- velocity across a strong magnetic field. The neutral atoms feel
- an electric field proportional to their perpendicular velocity
- times the magnetic field strength, and if this electric field
- is strong enough ionization can occur.
-
- * Lorentz Model - see Lorentz Gas
-
- % Los Alamos Meson Physics Facility (LAMPF): Physics research
- facility at Los Alamos National Lab; major site for U.S.
- muon-catalyzed fusion research in the 1980s. May be shut down soon.
-
- % Los Alamos National Laboratory (LANL): Major DOE research
- facility, located in Los Alamos, New Mexico, about an hour west of
- Santa Fe. Former home of a frozen-deuterium-fiber Z-pinch device,
- which was dismantled. Home to an active theory division, including
- the Numerical Tokamak Grand Challenge (being performed on the CM-5
- massively-parallel supercomputer).
-
- Also home to former alternative-concepts experimental devices like
- Scyllac, FRX-A, FRX-B, FRX-C/LSM, ZT40, and the aborted CPRF which
- was killed in 1991 when it was almost complete (budget cuts).
-
- Currently there are some small in-house experiments, including one on
- electrostatic confinement as a possible fusion device, and/or a
- compact neutron source. They also do theory and experimental
- collaboration with other labs worldwide.
-
- (Information provided by John Cobb and Ed Chao)
-
-
- * Loss Cone: (from John Cobb, with modifications and additions)
- In a magnetic mirror machine, particles with a large velocity
- parallel to the magneitc field and a small velocity perpendicular
- to the field will be able to escape past the magnetic mirror
- (see magnetic mirror). In that case the velocity distribution
- function (see distribution function) will be almost zero in the
- region of velocity space that allows particles to escape. The
- shape of that region (in a velocity space diagram with parallel
- velocity and perpendicular velocity as the axes) is a cone. When a
- particle undergoes a collision, its velocity gets somewhat
- randomized. Particles that are scattered into that cone are lost very
- quickly (in one mirror bounce time). Thus it is called a loss cone.
- Because of the loss cone, the theoretical maximum particle
- confinement time of a magnetic mirror machine can be only a few times
- the particle collision time; this is generally seen as a showstopper
- for mirror-based fusion research.
-
- * Loss of Coolant Accident (LOCA): Powerplant accident where
- the supply of coolant to the hot power-producing core is
- interrupted, or where the coolant drains out for some reason.
- Can lead to meldown of a fission reactor core in extreme cases,
- or to small nuclear explosions (e.g., Chernobyl). Fusion
- reactors are expected to be less vulnerable to LOCAs, but these
- must still be designed for.
-
- * Low-activation materials: In fission reactors, one is forced
- to deal with the radioactive byproducts of the fission process,
- but in fusion reactors one generally has a choice of what materials
- to expose to neutrons produced by the fusion process. A major
- problem for fusion reactors is developing materials (such as for
- the reactor vacuum vessel structure) which can be exposed to
- high levels of neutron bombardment without becoming permanently
- radioactive. Candidate structural materials which have
- relatively low induced radiactivation (generally relative to
- stainless steel) are known as low-activation materials; these
- include titanium, vanadium, and silicon-carbide.
-
- * Low Aspect Ratio: (entry from John Cobb, slightly edited)
- An aspect ratio for a torus that is small (minor radius is almost as
- big as major radius). There are many fusion devices which are
- designed to have a low aspect ratio. Such devices look more like
- tractor tires than bicycle tires, as toruses go. There are reasons
- to believe that low aspect ratio devices will offer some advantages
- for a fusion reactor. Usually, ease of theoretical and/or numerical
- analysis is not one of these advantages :>.
-
- * Low-beta plasma: a plasma in which the beta value (see entry)
- is typically 0 to 0.01.
-
- * Low mode or L-Mode: (from Herman) The "normal" behavior of
- a tokamak plasma, characterized by poor confinement and a particular
- scaling of decreasing confinement with increasing temperature.
-
- * Lower hybrid frequency:
-
- * Lower Hybrid Heating: form of RF heating using Lower Hybrid Waves.
-
- * Lower Hybrid Waves: "Electrostatic ion oscillations at a frequency
- intermediate to the electron extraordinary wave (high frequency) and
- the magnetosonic wave (low frequency). Not waves, strictly speaking,
- because they do not propagate (I think)."
- - Albert Chou, albert@seas.ucla.edu
-
- * Luminescence: Light emission that cannot be attributed merely
- to the temperature of the emitting body, but results from such
- causes as chemical reactions at ordinary temperatures, electron
- bombardment, electromagnetic radiation, and electric fields.
-
-
-
-
-
-