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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 19/26 (S)
- Supersedes: <fusion-faq/glossary/s_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:26:16 GMT
- Organization: Princeton University
- Lines: 342
- Approved: news-answers-request@MIT.EDU
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/s_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: 1995/02/26
- Originator: faqserv@penguin-lust.MIT.EDU
- Xref: senator-bedfellow.mit.edu sci.physics.fusion:44267 sci.answers:10864 news.answers:170850
-
- Archive-name: fusion-faq/glossary/s
- 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 19: Terms beginning with "S"
-
- 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).
- ==================================================================
-
- SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
-
- @ (?) SHIVA: see entry under Shiva, below.
-
- @ SI: Systeme Internationale; see SI Units
-
- @ SM: Symmetric Mirror
-
- @ SN: Single Null; see entry for Divertor
-
- @ SNL: Sandia National Laboratories; see entry
-
- @ SOL: Scrape-Off Layer; see entry
-
- @ STM: Symmetric Tandem Mirror experiment.
-
- $ Sv: Sievert; see entry
-
- * Safety Factor: (q) The number of times a field line goes around a
- torus "the long way" for each time around "the short way". In a
- tokamak, this number is typically near unity in the center of the
- plasma and between two and 6 or 8 at the edge. So-called because it
- helps to determine the degree of stability the plasma has against
- certain instabilities. The safety factor is the inverse of the
- rotational transform, and can be expressed mathematically
- as q = (r * Bt )/(R * Bp), where r and R are the minor and major
- radii of the torus, and Bt and Bp are the toroidal and poloidal
- magnetic fields.
-
- ! Sakharov, Andrei: Russian physicist; among other achievements, he
- is credited with the initial design of the tokamak.
-
- % Sandia National Laboratories: Located in Albuquerque, New Mexico.
- Another large DOE laboratory; has PBFA-II (Particle Beam Fusion
- Accelerator, an ICF device) and some pinch devices. Some divisions
- located in Livermore (Sandia-Livermore).
-
- * Sawtooth: When a tokamak runs with enough current to achieve
- q < 1 on the magnetic axis, the plasma parameters (n, T, B)
- oscillate with a "sawtooth" waveform. The oscillation is
- localized to a region roughly within the q=1 surface, and
- arises from internal MHD effects. Confinement is degraded
- within the sawtooth region.
-
- * Scaling Laws: These are mathematical rules explaining how
- variation in one quantity affects variations in other quantities.
- For instance, in a tokamak reactor it's generally believed that
- energy confinement depends on the size of the device and the strength
- of the magnetic field, but the precise nature of the dependence is
- not fully understood, so empirical "scaling laws" are tested to
- see what the dependence is. Scaling laws are useful for extrapolating
- from parameter regimes where the mathematical relationships
- between the various quantities are known, into unexplored regimes.
-
- & Scattering: The deflection of one particle as a result of
- collisions with other particles or with waves. See also Elastic.
-
- * Schlieren Method: An optical technique that detects density
- gradients occuring in a fluid flow. In its simplest form, light
- from a slit is collimated by a lens and focused onto a knife
- edge by a second lens; the flow pattern is placed between the
- two lenses, and the resulting diffraction pattern is observed on
- a screen or photographic film placed behind the knife edge.
-
- * Scientific Feasibility: Fusion will be considered scientifically
- feasible when (a) experiments are done which reach scientific
- breakeven-type plasma conditions (see entry on breakeven), and
- (b) the experimental results suggest that the approach can be
- "scaled up" into a power-producing system. Tokamak fusion
- reactors are closing in on (a), and tokamak researchers think
- (b) holds as well, so they are designing a power-producing
- machine (ITER) to demonstrate net energy production from tokamak
- fusion. Inertial confinement is also approaching this point.
-
- * Scrape-Off Layer (SOL): [from Art Carlson] Outer layer of a
- plasma which is affected ("scraped off") by a divertor or limiter.
- That is, the outer layer of a magnetically confined plasma (ca. 2 cm
- thick) where the field lines penetrate a material surface (limiter or
- divertor plate) rather than close upon themselves. This region
- defines the outer limit of the plasma because any plasma crossing
- into the SOL is rapidly lost since transport along the field is much
- faster than that across the field. That is, particles follow these
- field lines into the material surface and are lost from the plasma.
-
- * Screw Pinch: A variant on the theta pinch, in which axial
- currents (as in a z pinch, but less intense) produce a poloidal
- magnetic field (in addition to the usual longitudinal field),
- thus making a corkscrew field configuration. See also theta pinch,
- z pinch, pinch device.
-
- * Second-stability Region: A high pressure region where the plasma
- becomes stable to the pressure-gradient-driven ballooning
- ballooning instability. The plasma is stable in the limit of
- small pressure gradients, becomes unstable at some intermediate
- pressure, and then becomes stable again at still higher pressures.
- Tokamaks operating in the second-stability region would be more
- attractive because the higher pressures (beta) would provide more
- fusion reactivity per unit volume of plasma, allowing smaller
- reactors to be built.
-
- * Separatrix: [from Art Carlson] In a divertor tokamak (and some
- other configurations), the last closed flux surface (see entry) is
- formed not by inserting an object (limiter) but by manipulating the
- magnetic field, so that some field lines take a topologically
- different route (through the divertor, rather than simply around the
- central plasma). The boundary between the two types of field lines is
- called the separatrix.
-
- * Sheared Flow: Fluid flow where the magnitude of the fluid velocity
- changes along a direction perpedicular to the direction of the fluid
- flow. (Freeway traffic often exhibits sheared flow in that traffic
- in the "fast lane" moves more rapidly than traffic in the slow lane
- with the exits...) Sheared flow typically correlates with reduced
- transport and enhanced confinement. (This definition is rather
- informal and may not be fully technically correct - R.F. Heeter)
-
- * Shear Fields: As used in plasma physics, this refers to magnetic
- fields having a rotational transform (or, alternatively, safety
- factor) that changes with radius (e.g., in the stellarator concept,
- magnetic fields that increase in pitch with distance from the
- magnetic axis.)
-
- * Sheath: See Debye Sheath
-
- > Shiva: 20-beam Nd-glass fusion laser facility at LLNL. Was
- completed in 1977 and used for target irradiation experiments
- until mid-1981. Succeeded by Nova.
-
- * Shock Heating: Heating produced by the impact of a shock wave.
-
- * Shock Tube: A gas-filled tube used in plasma physics to
- quickly ionize a gas. A capacitor bank charged to a high voltage
- is discharged into the gas at one tube end to ionize and heat
- the gas, producing a shock wave that may be studied as it
- travels down the tube.
-
- * Shock Wave: Wave produced (e.g., in a gas or plasma) as a
- result of a sudden violent disturbance. To produce a shock
- wave in a given region, the disturbance must take place
- in a shorter time than the time required for sound waves to
- traverse the region.
-
- $ Sievert: International unit for radiation dose. One Sievert
- equals 100 rem (see entry for rem); average per-capita exposure
- is about 0.3 Sv, primarily from natural background (see entry)
- and medical x-rays.
-
- * Shock Heating: The heating produced by the impact of a shock wave.
-
- * Shock Wave: Wave produced as a result of a sudden, violent
- disturbance which occurs in a particular region faster than sound
- waves can traverse the region.
-
- * Shot: Fusion jargon for the production of a (short-lived) plasma.
- In the early days, plasmas were produced by the "discharge" of
- capacitor banks, which (frequently) made a BANG. A modern tokamak
- produces a few dozen "shots" per day, each lasting a few seconds and,
- if nothing goes wrong, inaudible. See also: capacitor, tokamak
- (Arthur Carlson, awc@ipp-garching.mpg.de)
-
- $ SI Units: (also known as MKS, MKSA Units) System of measurement
- in which the fundamental units are meters, kilometers, seconds, and
- the ampere.
-
- $ Sievert: Unit of absorbed radiation dose equivalent to 100 rem.
- (see also rem, rad, Gray) The sievert is based on the Gray in the
- same way that the rem is based on the rad, I believe.
-
- & Solenoid: Cylindrical coil of wire which, when current
- flows through it, acts as an electromagnet. For long solenoids
- with many turns, the magnetic field inside the center is
- nearly uniform.
-
- * Solid Breeder: Solid lithium-bearing compounds, usually
- ceramics such as Li2O and LiAlO2, which might be used in the
- blanket of a D-T fusion reactor to produce ("breed") additional
- tritium fuel from the n + Li => He + T (+n) reactions.
-
- * Solid State Laser: A laser using a transparent substance
- (crystalline or glass) as the active medium, doped to provide
- the energy states necessary for lasing. The pumping mechanism
- is the radiation from a powerful light source, such as a
- flashlamp. The ruby, Nd-YAG, and Nd:glass lasers are
- solid-state lasers.
-
- * Solitons: Stable, shape-preserving and localized solutions
- of nonlinear classical field equations. Of recent interest
- as possible models of extended elementary particles.
-
- * Sound Waves: See entries on compression waves, waves.
-
- * Space Frame or Spaceframe: Three-dimensional "optical bench"
- that holds laser components stable from vibrational and
- thermal excursions.
-
- * Spallation: See radiation damage, surface.
-
- * Spatial Filter: Device consisting of a lens pair and a pinhole
- aperture stop. Intensity fluctuations over the spatial extent
- of a laser beam are removed by passing the focused beam through
- the aperture stop. The pinhole must be placed in a vacuum to
- prevent air breakdown by the focused beam. These filters are
- used to counter the effects caused by self-focusing.
-
- > Spherator: Single-ring multipole device with an additional
- current-carrying rod perpendicular to the ring axis.
-
- > Spheromak: [from Art Carlson] A compact torus with comparable
- toroidal and poloidal magnetic fields. The plasma is roughly
- spherical and is usually surrounded by a close-fitting conducting
- shell or cage. Both the poloidal and toroidal magnetic fields
- are generated by plasma currents. There are no toroidal field
- coils "linking" the plasma through the central plasma axis.
- External force is supplied by poloidal field coils outside
- the plasma separatrix. The resulting configuration is approximately
- a force-free magnetic field. The spheromak machine geometry can
- be simpler than a tokamak, but the close-fitting wall is a source
- of impurities and the current cannot be inductively driven. After
- early experiments failed to achieve a reasonable beta, interest
- has ebbed. The spheromak can also be considered as the
- low-aspect-ratio limit of the tokamak. See also: compact torus.
-
- * Spin-Polarized Fusion: A method to enhance nuclear fusion
- reaction rates in some fusion fuels by polarizing the nuclear
- spins.
-
- ! Spitzer, Lyman: Early Princeton Fusion Scientist;
- astrophysicist who first proposed orbiting space telescope;
- inventor of the stellarator.
-
- & Spontaneous Emission: Radiation randomly emitted by excited
- atoms or ions. Contrast with stimulated emission.
-
- * Sputtering: Process by which atoms are ejected from a solid
- surface by bombardment with plasma particles. See entry
- for "Radiation Damage, Surface."
-
- * Stability: characteristic of some types of equilibrium states;
- see equilibrium.
-
- > Starfire Tokamak: A conceptual design study of a modular
- tokamak reactor that operates in a steady-state condition
- while using conventional power-generating systems.
-
- & Stark Effect: The effect an electric field has on the
- spectral lines emitted from excited atoms. The effect may
- arise from externally-applied electric fields, from internal
- fields due to the presence of neighboring ions or atoms (pressure),
- or from the electric field associated with the Lorentz
- (v cross B) force (motional stark effect). Spectroscopic
- measurements of plasmas using the pressure-based and motional
- Stark effects are useful for diagnostic purposes.
-
- > Stellarator: (adapted from Herman) Device invented by Lyman Spitzer
- for the containment of a plasma inside a racetrack-shaped
- (sometimes a figure-8) tube. The plasma is contained by a magnetic
- field created by helical windings around the tube. More generally,
- a toroidal sort of device that attempts to average out particle
- drifts that would otherwise take plasma to the walls of the vacuum
- vessel by imposing a given amount of helicity to the toroidal field
- lines. "A toroidal plasma configuration, which, unlike a tokamak,
- is not axially symmetric. The poloidal fields necessary for
- confinement are produced by external coils (rather than a current
- in the plasma), either helical coils in addition to plane toroidal
- field coils, or out-of-plane toroidal field coils (pioneered in
- Germany on Wendelstein 7-AS). The stellarator is generally
- considered to be the most serious alternative to the tokamak. Since
- the concept is inherently steady state, it would not have the
- tokamak's problems with thermal and mechanical cycling, current
- drive, and disruptions."
- -- Arthur Carlson, awc@ipp-garching.mpg.de
-
- & Stimulated Emission: Radiation coherently emitted by excited
- ions when driven by a passing light wave and the appropriate
- transition wavelength. "Laser" means Light Amplification by
- Stimulated Emission of Radiation; it occurs when there is a
- population inversion between the upper and lower energy states
- of the transition, such that stimulated emission can dominate
- excitation. Stimulated emission is coherent and codirectional
- with the stimulating wave, and the rate of stimulated emission
- is proportional to the intensity of the stimulating wave.
-
- * Strong (Nuclear) Force:
-
- * Sturm-Liouville Problem: The general problem of solving a
- linear differential equation of order 2n, together with
- 2n boundary conditions; also known as the eigenvalue problem.
-
- * Superconductor: A type of electrical conductor that permits
- a current to flow with zero resistance. Without superconducting
- coils, a toroidal magnetic-confinement fusion reactor would not
- be possible, because too much energy would be required to
- maintain the magnetic fields against resistive energy losses
- in the coil conductors.
-
- * Suydam Stability Criterion: A criterion for the stability
- of modes localized arbitrarily close to a mode-rational surface
- (see rational surface) in a circular cylindrical geometry.
-
- & Synchrotron Radiation: (Also known as cyclotron radiation.)
- Electromagnetic energy radiated from a charged particle moving
- in a curved orbit (typically in a magnetic field), due to the
- acceleration required to change the direction of the particle's
- velocity. See also bremsstrahlung.
-
- * Symmetry axis: [from Art Carlson] The straight line (usually
- vertical) through the center of a configuration, when the
- configuration is symmetric to all (axisymmetric, like the tokamak)
- or some (periodic, like the stellarator) rotations about this
- line. Usually the z-axis.
-
-
-
-