Subject: Conventional Fusion FAQ Glossary Part 19/26 (S)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:43 GMT
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.
Subject: Conventional Fusion FAQ Glossary Part 20/26 (T)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:47 GMT
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.
Subject: Conventional Fusion FAQ Glossary Part 23/26 (W)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:52 GMT
Archive-name: fusion-faq/glossary/w
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 23: Terms beginning with "W"
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).
==================================================================
WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
# W: Chemical symbol for Tungsten
@ W-7AS, W-7X: See Wendelstein entry
* Wall Conditioning: Describes a class of procedures used to
control the composition of materials adsorbed onto the walls of
a plasma device. Conditioning is important because material from
the walls can create impurities in the plasma, and these
impurities typically degrade plasma performance. See also
boronization, impurity control, electron cyclotron discharge
cleaning.
* Wall Loading: Fusion reactor thermal output power divided
by the area of the wall facing the plasma. (Neutron wall
loading is 4/5 of the total for D-T fusion.)
& Waste, Radioactive: See Radioactive Waste.
& Wavelength: The length of a single cycle of a wave; usually
measured from crest-to-crest. For electromagnetic waves, the
wavelength determines the type (radio, infrared, visible,
ultraviolet, X-Ray, gamma-ray) of radiation; in the case of
visible light, wavelength determines the color of the light.
& Waves:
& Weak (Nuclear) Force:
> Wendelstein: A family of stellarators built in Garching, Germany.
The machine currently in operation is Wendelstein-7AS (aka W-7AS).
Wendelstein ("spiral rock") is a craggy Bavarian mountain; some of
W-1 through W-6 were built, some were just paper studies; AS stands
for "advanced stellarator" and refers on the physical side to an
attempt to minimize neoclassical effects (see entry for Neo-classical
Diffusion) such as the bootstrap current (see entry), and on the
technical side to the use of out-of-plane coils as an alternative to
linked coils. W-7X, a much larger, superconducting stellarator based
on the same concepts has been proposed to be built by the European
Union in Greifswald, on the north coast of Germany.
* Whistler: A wave in a plasma which propagates parallel to the
magnetic field produced by currents outside the plasma at a frequency
less than that of the electron cyclotron frequency, and which is
circularly polarized, rotating in the same sense as the electrons
in the plasma (about the magnetic field); also known as the
electron cyclotron wave. Whistlers are so-named because of their
characteristic descending audio-frequency tone, which is a result
of the dispersion relation for the wave (higher frequencies
travel somewhat faster). This tone was frequently picked
up during World War I by large ground-loop antennas (which were
actually being used to spy on enemy field telephone signals).
% Wisconsin - See University of Wisconsin-Madison
Subject: Conventional Fusion FAQ Glossary Part 8/26 (H)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:04 GMT
Archive-name: fusion-faq/glossary/h
Last-modified: 4-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 8: Terms beginning with "H"
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).
==================================================================
HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
# H: chemical symbol for the element hydrogen; see entry
# He: chemical symbol for the element helium; see entry.
@ HIREX: High-REsolution X-ray spectroscopy
@ H-mode: see high-mode
@ HTO: (Hydrogen-Tritium-Oxygen) Water with a tritium atom
replacing a hydrogen. See entry for tritium.
* Half-life: For a given quantity of a radioactive isotope,
there is a time period in which half the nuclei will decay to
a different state; this period is called the half-life. Measured
half-lives range from less than millionths of a second (for very
short-lived isotopes) to billions of years (for isotopes which
are almost stable, but not quite). The time in which half the
atoms of a particular radioactive isotope disintegrate
to another nuclear form. By analogy, "half-life" can also be
used to describe similar time-periods for other sorts of
exponential decay phenomena.
* Hall Effect: Transverse electric field which develops in a
conductor (as a result of the Lorentz Force acting on the charge
carriers) when current is driven across a magnetic field.
* Halo: The cold, dense plasma formed outside the last closed flux
surface during a vertical displacement event. The large currents
which flow through this plasma stop the displacement and transfer the
force to the vacuum vessel. If care is not taken in design, the halo
currents can be large enough to threaten the structural integrity of
the vacuum vessel or in-vessel components. Whereas the center of a
tokamak plasma is too hot for material probes to survive, probes
(such as magnetic-field coils) can sometimes be placed in the
halo, and can measure things such as the halo current (see below).
See also entry for vertical instability.
* Halo Current: Currents in the halo region of a plasma discharge.
See entry for halo above.
* Hamada coordinates: A particular magnetic-flux coordinate
system useful for MHD calculations. In this system the current
density and magnetic field lines are straight and the Jacobian
of the coordinate transformation equals one.
& Hamiltonian Function: Function arising from the Hamiltonian
approach to mechanics which characterizes the total energy of
a system as a function of generalized coordinates and momenta
and can be used to obtain the dynamical equations of motion
of the system. (Consult an intermediate or advanced mechanics
text for more info.)
> Hard-core pinch device: plasma pinch-discharge device using a
solid central conductor ("hard-core"). The discharge then occurs
in an annular region about the central conductor.
& Hartree-Fock approximation: a refinement of the Hartree method
(see entry) in which one uses determinants of single-particle
wave functions rather than products, thereby introducing exchange
terms into the Hamiltonian.
& Hartree method: An iterative, variational method of finding an
approximate quantum-mechanical wavefunction for a system of many
electrons, in which one attempts to find a product of
single-particle wave functions, each of which is a solution of
the Schrodinger equation with the field deduced from the charge
density distribution due to all the other electrons; also known
as the self-consistent field method.
& Heat exchanger: device that transfers heat from one fluid
(liquid or gas) to another (or to an external environment).
* Heavy Hydrogen: somewhat informal alternative name for deuterium.
(see entry for deuterium).
* Heavy Water: (D2O) Water with enriched content of deuterium
relative to hydrogen (greater than the natural abundance of 1 D
per 6500 H). Heavy water is used as a moderator in some fission
reactors (see CANDU entry) because it slows down neutrons effectively
but also has a low collision cross-section for absorption of neutrons.
> Heliac: A confinement configuration which superimposes an l=1
stellarator-type field upon a tokamak-like poloidal field. The
resulting plasma configuration is a helix bent around into a loop.
* Helicity: (from John Cobb) A measurement of the topological
"tangledness" of magnetic field lines. It is formally defined as the
scalar product of the magnetic vector potential with the magnetic
field, K = A dot B. If the plasma is perfectly conducting, then
helicity is a conserved quantity. (Without resistance, field lines
cannot reconnect, and magnetic topology is conserved, so helicity is
conserved). (See frozen-in flow). If the plasma has a small amount
of resistivity, then Helicity is not exactly conserved. However, the
total helicity inside of a given flux surface is often conserved to a
good approximation. In that case, the dynamics of a plasma can be
analyzed as an evolution toward a minimum energy state subject to the
constraint of a conserved total helicity (See Taylor State, J.B.
Taylor). This is often used in analyzing the equilibrium and
relaxation of RFP's and other toroidal devices.
> Helios Facility: Los Alamos laser inertial fusion facility.
& Helium: Element whose nuclei all contain two protons.
Stable isotopes are 3He and 4He. 3He is rare on earth (only 1.3
ppm of naturally-occuring He), can be generated from decaying
tritium (half life of about 12 years), and is relatively abundant
in the crust of the moon. Helium is the second most abundant element
in the universe and in the sun, and occurs at about (I believe)
1 part per million in earth's atmosphere. Helium is also found
in significant quantities in natural gas deposits. The nucleus
of the He atom is also known as an alpha particle. Helium is
chemically inert, behaves nearly as an ideal gas under a wide
range of pressures and temperatures, and can only be liquefied
at 4 Kelvin (at atmospheric pressures). One mole of He weighs
4 grams.
! Hertz, Heinrich: 19th-century German physicist; first (?)
observed low-frequency electromagnetic waves.
$ Hertz: Unit of frequency equal to one complete oscillation (cycle)
per second. Common abbreviation is Hz.
* High-beta plasma: A plasma in which the beta value (see entry)
is typically 0.1 to 1.
* High-mode or H-mode: A regime of operation most easily
attained during auxiliary heating of diverted tokamak
plasmas when the injected power is sufficiently high.
A sudden improvement in particle confinement time leads to
increased density and temperature, distinguishing this mode
from the normal "low mode." However, H-mode has been achieved
without divertors, auxiliary heating, or a tokamak. (H-modes
have been observed in stellarators.)
& Holography: A technique for recording and later reconstructing
the amplitude and phase distribution of a wave disturbance.
& Homopolar generator: A direct-current generator in which the
poles presented to the armature are all of the same polarity,
so that the voltage generated in the active conductors has the
same polarity at all times. A pure direct current is thus
produced without commutation.
* Hot cells: Heavily radiation-shielded enclosure in which
radioactive materials can be handled by persons using remote
manipulators and viewing the materials through shielded windows
or periscopes.
* Hybrid diode: An ion diode that uses a field coil in series
with the ion diode's accelerating gap to generate sufficient
magnetic flux in the diode for electron control. The diode is
a combination of the Applied-B diode's ion source and the
Ampfion diode's field coil.
* Hybrid reactor: see fusion-fission hybrid.
* Hybrid resonance: A resonance in a magnetized plasma which
involves aspects of both bunching of lighter species parallel
to the magnetic field, characterized by the plasma frequency;
and perpendicular particle motions (heavier species) characterized
by the cyclotron frequency.
& Hydrogen: (H) Element whose nuclei all contain only one proton.
Isotopes are protium (p, no neutrons) deuterium (D or d,
one neutron), and tritium (T or t, two neutrons). Hydrogen is
the lightest and the single most abundant element in the
universe, and in the sun. Hydrogen is a major element in
organic compounds, water (H2O), and many other substances.
Hydrogen is ordinarily a gas, but can be liquefied at low
temperatures, and even solidified at low temperature and
high pressure. Hydrogen gas can burn explosively
in the presence of oxygen.
* Hydrogen bomb or H-bomb: (from Herman) An extremely
powerful type of atomic bomb based on nuclear fusion.
The atoms of heavy isotopes of hydrogen (deuterium and
tritium) undergo fusion when subjected to the immense
heat and pressure generated by the explosion of a nuclear
fission unit in the bomb.
* Hydrogen embrittlement: A decrease in the fracture
strength of metals (embrittlement) due to the incorporation
of hydrogen within the metal lattice.
* Hydromagnetic Instability: See MHD Instability
* Hydromagnetics: see magnetohydrodynamics (MHD)
Subject: Conventional Fusion FAQ Glossary Part 15/26 (O)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:29 GMT
Archive-name: fusion-faq/glossary/o
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 15: Terms beginning with "O"
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).
==================================================================
OOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO
@ OFE: Office of Fusion Energy; see entry
@ OH: Ohmic Heating; see entry
@ OH1, OH2L, OH2U: Ohmic Heating Coils (1,2, upper, lower)
on Alcator C-Mod
@ OPEC: Organization of Petroleum Exporting Countries; see entry
@ ORNL: Oak Ridge National Laboratory; see entry
% Oak Ridge National Laboratory: Located in Oak Ridge, TN.
Home of a series of various fusion devices. Recent machines
have included the Elmo Bumpy Torus and the Advanced Toroidal
Facility (stellarator). (Could use more info!)
% Office of Fusion Energy: This is the office (within the
Office of Energy Research in the U.S. Department of Energy)
which administers the fusion energy research program.
Web users can visit http://wwwofe.er.doe.gov/ for more info.
! Ohm, Georg Simon (1789-1854): Physicist who discovered the
relationship between electric current, potential and resistance.
(Yes, it is Georg. Swedish, I believe.)
$ Ohm: Unit of electrical resistance.
& Ohmic heating: Heating that results from the flow of current
through a medium with electrical resistance. In plasmas
subjected to ohmic heating, ions are heated almost entirely by
transfer of energy from the hotter, more mobile electrons.
* Ohmic heating coil: On a tokamak, this is the coil (generally
a set of coils; part of the poloidal field system) used to
induce an electric field in the plasma via a transformer
effect. The electric field generates of a toroidal plasma
current, with resultant ohmic heating.
* Ohmic heating solenoid: See ohmic heating coil, solenoid.
& Ohm's Law: The relationship between the net current and
the electric field in a conducting medium. For simple
resistors, the voltage equals current times resistance,
V = I*R. In plasmas the "generalized Ohm's Law" is a
more complex tensor relationship involving the vector
current density, the vector for the electric field, and
a generalized resistance tensor that relates the two.
> OMEGA: Inertial confinement fusion facility at the Laboratory
for Laser Energetics, University of Rochester (NY). OMEGA
uses a 24-beam Nd:glass laser at wavelengths of
1.054 or .351 microns.
# Omega: Variable frequently used to denote frequencies.
* O-Point: Place where the poloidal magnetic field vanishes in such
a way that the nearby flux surfaces are elliptical, e.g. on the
magnetic axis (see entry) or at the center of a magnetic island (see
entry). (See also X-Point.)
& Optical Axis: The line passing through both the centers of
curvature of the optical surfaces of a lens; the optical
centerline for all the centers of a lens system.
& Optical Interferometer: This is an interferometer (see entry)
which uses the interference of optical-frequency light waves.
These are useful in measuring distances precisely, and can
be used to test optical system elements (lenses, mirrors, etc.)
during manufacture.
* Optical Pumping: In laser physics, this denotes the process
in which absorbed light is stored in the laser medium. If the
absorption & storage process creates a population inversion,
laser action can occur (and extract the energy stored by optical
pumping in the form of laser emission).
* Oscillator: In laser physics, this refers to a device to
generate coherent optical energy. (i.e., it's another term
for the laser-light creating device itself, minus the source
of power which pumps the oscillator.) The oscillator generally
consists of a laser medium placed within an optical resonant
cavity (pair of mirrors). Optical energy will be trapped between
the mirrors and the optical (laser) oscillations will grow
so long as the gain of the laser medium exceeds the losses at
the mirrors.
* Outboard Side: portion of a tokamak / toroidal device on
the outer side, opposite the central axis.
* Overturning Moment: Torque ("moment") on a toroidal field
coil in a tokamak, about the device's radial direction,
that results from out-of-plane forces on the coil due to
the interactions between the coil current and the poloidal
(vertical) magnetic field. This torque tends to "overturn"
the vertical toroidal field coil, and must be engineered
against.
Subject: Conventional Fusion FAQ Glossary Part 4/26 (D)
From: Robert F. Heeter
Date: 23 Nov 1996 06:14:36 GMT
Archive-name: fusion-faq/glossary/d
Last-modified: 4-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 4: Terms beginning with "D"
FREQUENTLY USED TERMS IN CONVENTIONAL FUSION RESEARCH
AND PLASMA PHYSICS
Edited by Robert F. Heeter, rfheeter@pppl.gov
Guide to Categories:
* = vocabulary specific to plasma/fusion/energy research
& = basic/general 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).
==================================================================
DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
@ D: nuclear/chemical symbol for deuterium/deuteron
@ DC, dc: Direct Current; see entry
@ DCLC: Drift Cyclotron Loss Cone instabilities; see entry.
@ DT: Deuterium-Tritium; see entry labeled DT Fuel
@ DIII-D: not an acronym (anymore); see entry
@ DOE: Department of Energy (United States); see entry
@ dpa: Displacements per atom; see entry
@ DPP: Division of Plasma Physics; see APS-DPP
* D-shaped plasma: A toroidal plasma whose cross section
(poloidal plane) is a D (instead of a circle). A D-shape
has a higher beta limit (see entry) than a circular shape.
* Debye Length: The characteristic distance over which charges are
shielded in a plasma. See also: Debye shielding.
lambda_D = ( epsilon_0 k_B T_e / (n_e e^2) )^(1/2)
lambda_D[m] = (7.434*10^3)*(_e[eV])^(1/2)*n[m^(-3)]^(-1/2)
(Arthur Carlson, awc@ipp-garching.mpg.de)
! Debye, Peter Joseph: Physical chemist, studied behavior of
conductive solutions (plasmas have some similar behaviors).
* Debye Radius: See Debye Length.
* Debye Sheath: The region of strong electric field in front of
a material surface in contact with a plasma. Its characteristic
thickness is the Debye length, and it is caused by Debye shielding
of the negative surface charge resulting from electrons flowing to
the surface much faster (initially) than the ions. The lost
electrons leave behind a region of net positive charge which
gradually diminishes the strength of the electric field
over the debye length. See also: Debye Length, Debye Shielding.
(Arthur Carlson, awc@ipp-garching.mpg.de, with modifications by
John Cobb, johncobb@uts.cc.utexas.edu)
* Debye Shielding: If a positive (or negative) charge is inserted
into a plasma, it will change the local charge distribution by
attracting (repelling) electrons. The net result is an additional
negative (positive) charge density which cancels the effect of the
initial charge at distances large compared to the Debye length.
(There is a corresponding effect of shielding by the ions, which,
for various and subtle reasons, usually is less important.)
See also: Debye Length.
(Arthur Carlson, awc@ipp-garching.mpg.de)
* Debye Sphere: Sphere around a charged test particle whose
radius is equal to the Debye length.
& Decay, Radioactive: See radioactive decay.
* Decay Modes: Different pathways for decay of radioactive nuclei.
The decay modes for a given unstable state can include beta
emission (negative = electron, positive = positron), electron
capture, alpha emission, fission, and gamma emission.
(Did I miss any?) See entries for each mode for more information.
* Dee-Shaped: see D-shaped plasma above.
* Degenerate Configuration: Magnetic field configuration in
which the magnetic lines of force close exactly on themselves
after passing around the configuration a finite number of times.
* Dense Plasma Focus: See Plasma Focus. (Densities of up
to 10^26 particles/m^3 have been reported.)
& Density: amount per unit of volume, or per unit surface area, or
per unit length. (Usually specified or clear from context which
of these is meant). Several types:
Charge density - amount of charge per unit (volume, area, length)
Current density - current flow per unit transverse surface area.
Energy density - amount of energy per unit volume.
Flux density - flux per unit of transverse surface area.
Mass density - mass per unit volume.
Number density - number of particles per unit volume.
Particle density - same as number density.
% Department of Energy: (DOE) Department within the
executive branch of the U.S. government (at the cabinet
level) which has managed and overseen federally-sponsored
energy research. The DOE was formed in 1977 from ERDA,
the Energy Research and Development Administration,
and (I think) the Atomic Enegy Commission (AEC).
& Deuterium: A heavy isotope of hydrogen whose nucleus
contains both a neutron and a proton.
* Deuteron: A deuterium ion; nucleus consisting of a proton
and a neutron.
* Diagnostics: (from Herman) Procedures for determining
(diagnosing) the state of a plasma during an experiment;
also refers to the instruments used for diagnosing.
* Diamagnetic Effects: Application of a magnetic field to a plasma
will tend to create circulating current within the plasma that will
reduce the strength of the magnetic field.
* Diffusion: The interpenetration of one substance into another
as a result of thermal / random motion of the individual particles.
(e.g., the diffusion of a plasma across a magnetic field as a
result of collisions which cause particles to move along new
field lines.) See also classical diffusion, neoclassical diffusion,
anomalous diffusion, transport.
* Direct Conversion: The generation of electricity by direct
recovery of the kinetic energy of the charged fusion reaction
products.
& Direct Current: Electric current which is unchanging in
time, or at least not oscillating. Opposite of Alternating Current.
* Direct Drive: An approach to inertial-confinement fusion
in which the energy of the driver (laser or particle beam)
is directly incident on the (usually spherical) target,
causing compression heating via ablation of the target surface.
* Dispersion Relation: For a given wave, the dispersion relation
relates the temporal frequency of a wave (w, or omega) to its
wavenumber k and other physical quantities characteristic of
the system. Dispersion relations can be quite simple
(e.g., w = k * c for light; c being the speed of light),
and they can also be quite complex, with interesting
mathematical structure. The dispersion relation and its
mathematical structure provide important information
about the wave, including the phase and group velocities.
(See relevant entries.) Note that the meaning of "dispersion
relation" is different in plasma physics than in other fields.
* Displacements Per Atom: (dpa) This is a measure of the
amount of radiation damage in neutron-irradiated materials;
e.g., 10 dpa means each atom in the material has been
displaced from its structural lattice site and average of
10 times (due to interactions between the atoms and the
energetic neutrons irradiating the material.)
* Disruption: Plasma instabilities (usually oscillatory modes)
sometimes grow and cause disruptions of the carefully-engineered
plasma conditions in the reactor. Major disruptions can cause
an abrupt temperature drop and the termination of the plasma.
Stored energy in the plasma is rapidly dumped into the rest
of the plasma system (vacuum vessel walls, magnet coils, etc.)
and can cause significant damage if precautions are not taken.
* Disruptive Instability: Instability which causes a disruption;
see entry for disruption.
* Dissociative Recombination: The combination of an electron
with a positive molecular ion, followed by dissociation of
the molecule in which the resulting atoms/molecules carry
off the excess energy released in the recombination.
& Distribution Function: Function characterizing the density of
particles located at a given point in phase space (a combination
of either velocity or position coordinates) at a given time.
The velocity-space distribution function gives the number of
particles with a particular velocity; the position-space
distribution function is synonymous with the particle density
in position-space. Different combinations of position and
spatial coordinates are useful in different problems.
* Divertor: Component of a toroidal fusion device that diverts
charged particles on the outer edge of the plasma into
a separate chamber where they strike a barrier and become
neutralized. In a reactor, the divertor would incorporate a
system for pumping out the neutralized particles as exhaust
from the machine. A divertor, like a limiter, prevents the
particles from striking and degrading the chamber walls
and dislodging secondary particles that would cool and
contaminate the plasma. Whereas a limiter is a material
object used to limit the shape of the plasma, a divertor is a
magnetic-field construction. The advantage of the divertor
is that it allows the neutralization region to be
removed from the main plasma. See also: limiter.
* Doppler Broadening: Frequency spreading which causes
broadening of single-frequency radiation (e.g., spectral
lines) when the radiating bodies (atoms, molecules, etc.)
have different velocities. Radiation from each individual
radiating body has a different Doppler shift, and
the collection of radiations at different frequencies
broadens the peak of the line in an intensity-vs-frequency
plot.
& Doppler Effect: Variation in the frequency of a
wave (as measured by an observer) due to relative motion
between the observer and the source of the wave.
(The observed frequency increases if the source is moving
towards the observer.)
& Doppler Shift: The amount of change in the observed
frequency of a wave due to the Doppler effect; sometimes
called the Doppler frequency.
> DIII-D: Latest in a series of tokamaks designed
by General Atomics (formerly GA Technologies) in San Diego
making plasmas with noncircular cross sections, including
kidney shapes and D-shapes.
* Doublet Device / Doublet Plasma: Tokamak-type devices
where the plasma cross-section is kidney-shaped, with
a deep indentation in the middle so that the plasma has
two major rings of current (on top and bottom).
* Drift Cyclotron Loss Cone Instabilities: (DCLC)
This is an electrostatic microinstability (frequencies
at harmonics of the ion cyclotron frequency) which is of
major concern in small mirror devices. Mode is driven
by radial gradients in the electron density, and causes
loss of ions due to non-conservation of magnetic moment
(see adiabatic invariant) as they interact with the mode,
and are dispersed in velocity space into the loss cone.
Stabilization is accomplished by increasing the plasma
size and by partially filling the loss cone with a
continuous extermal warm plasma stream.
* Drift Motion: Ordinarily particles placed in a magnetic
field will simply orbit in circles, but if the magnetic field
is not uniform, or curves, or there is an electrical field
perpendicular to the magnetic field, or another force is applied
perpendicular to the magnetic field, then the "guiding centers"
of the particle orbits will drift (generally perpendicular to
the magnetic field and to the applied force). There are several
sorts of drifts; refer to a plasma physics text for more
information (see Section 11: Bibliography). For a good
introduction at the undergraduate physics level, see Chen.
* Drift Pumping: A process that removes ions trapped in
a thermal barrier using radial transport induced by an
exterally-applied radiofrequency field tuned to resonate
with the azimuthal drift frequency.
* Drift Surface: Surface on which the guiding center of
a particle is constrained to move, due to the effects of
the laws of adiabatic invariance on its drift motion.
* Drift Velocity: Characteristic velocity at which the center
of a particle's orbit ("guiding center") drifts when drift motion
(see above) occurs.
* Drift Waves: Oscillations in a magnetically-confined plasma
arising in the presence of density gradients (such as at the
plasma's surface). These resemble the waves that propagate
at the interface of two fluids with different density in
a gravitational field.
* DT Fuel: (Deuterium-Tritium) Easiest fuel mixture to use
in achieving fusion; unless otherwise specified, probably refers
to a 50-50 (by numbers or by moles) mix of deuterium and tritium.
* Duty Factor: Ratio of the duration of time when a system is
actually operating to the total time for a complete cycle
of the system. e.g., if a tokamak experiment runs for 5 seconds
and then sits for 500 seconds while the power supplies are
recharged, then the duty factor is 1%. Similar to capacity
factor for powerplants.
* Dye laser: A type laser in which the active material
(the material which emits the laser light) is a dye.
These lasers are tunable when the dye has very large
molecules (such as acridine red or esculin) and the laser
action takes place between the first excited and ground
electronic states, because each of these states contains
a broad continuum band of vibrational-rotational levels.
Subject: Conventional Fusion FAQ Glossary Part 0/26 (intro)
From: Robert F. Heeter
Date: 23 Nov 1996 06:14:22 GMT
Archive-name: fusion-faq/glossary/intro
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-monthly
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 of Frequently Used Terms in Plasma Physics
and Fusion Energy Research
Edited by Robert F. Heeter, rfheeter@pppl.gov
### This file introduces the Conventional Fusion Glossary ###
# Editorial Note:
Like any discipline, fusion research has evolved terminology used
to facilitate discussion. This includes the scientific vocabulary
of the discipline, the names of various research machines and
devices used, the names of various researchers in the field, the
names of the various research labs and funding authorities, the
mathematical symbols used, and the acronyms frequently used as
shorthand for some of the above.
In the case of conventional (magnetic confinement, inertial
confinement, thermonuclear, muon-catalyzed, etc - but not Cold)
fusion, this terminology has grown to the point where newcomers
(including the author of the glossary!) may be intimidated by the
apparent obscurity of the discussions. This file is an attempt
to provide a comprehensive and detailed listing and explanation
of terms frequently used, so that those new to the group/field
will be able to understand what is being said, and to contribute
with a minimum of confusion and frustration. Many terms are still
missing, and some terms may have less-than-fully-correct entries,
so if you would like to see something added or changed, let me
know.
# Yes, it's a big glossary!
The last time I counted, there were roughly 1000 entries, occupying
something like 300 kilobytes. But everything is organized
alphabetically, and to make things even better, each entry is
coded by type (names, acronyms, types of machines, basic physics
terms, advanced plasma terms, etc). Hopefully this will make
the glossary easier to use.
# What's in the FUT:
We started with an initial list supplied by Jim Day
(Jim.Day@support.com). To this were added some comments from various
responses I received to the first draft. I then incorporated terms
from PPPL and other glossaries. Then acronyms, machine names,
and names of important scientists were added as they came.
I added categories for research and funding/political agencies,
tried to broaden the base of basic science terms, and wrote up
a few more preliminary definitions based upon explanations that
have appeared in the newsgroup and in my studies. Many of the
terms listed still do not have explanations given.
Recent drafts have been mostly incremental improvements to
the previous versions. New categories of terms have been made,
the organization has been improved, and of course definitions
have been added and improved.
The most recent project has been to incorporate terms from the
"Glossary of Fusion Energy" published in 1985 by the Office of
Scientific and Technical Information (OSTI) of the U.S. Department
of Energy. This has been a fairly major effort, which has
roughly doubled the size of the glossary.
My current plan for the Glossary is to write entries for terms
used in my classes. This will be useful to me, as part of
studying for my upcoming PhD qualifying exam, and hopefully will
also help incoming graduate students, both here and around the
world.
# What's Needed to Improve the FUT:
I am looking for additional contributions (and improvements) to
the list. It would be nice if people posting to the group could
occasionally take a few moments to include definitions of a few
terms used when you use them; in browsing through the group I
can then snip out the terms and definitions and simply paste
them into the evolving Glossary files. It also would be nice if
references to the FAQ and the Reading List / Bibliography
could be given to supplement the Glossary descriptions, at least
for some of the more complicated terms.
# Comment on Sources:
The terms and definitions occurring here represent a collection
of contributions from numerous sources. Rather than include
acknowledgements for each individual definition, I have made
blanket acknowledgements below. I have tried to include
citations in most cases where only a single textual source
was used.
# Acknowledgements for the Glossary:
! = someone I believe is a scientist
* = people who are not scientists so far as I know, organizations, etc.
! Jake Blanchard, blanchard@engr.wisc.edu - suggested we have a
list of acronyms too.
! Arthur Carlson, awc@ipp-garching.mpg.de - supplied additional
definitions, made corrections / amplifications / revisions to
earlier definitions.
! Edward Chao, ehchao@theory.pppl.gov - info on LANL fusion research,
additions and corrections to various definitions.
! Albert Chou, albert@seas.ucla.edu - supplied additional
definitions, made corrections / amplifications / revisions to
earlier definitions.
! John Cobb, johncobb@uts.cc.utexas.edu - lots o' definitions.
! James Crotinger, jac@gandalf.llnl.gov - additional definitions,
quality control, and comments on the usefulness of the FUT.
* Jim Day, jim.day@support.com - initial list of terms, additional
definitions, modifications to earlier definitions.
! Steve Fairfax, Fairfax@cmod.pfc.mit.edu - additional definitions
from the Alcator weekly reports.
* Robin Herman, _Fusion: Search for Endless Energy_; I borrowed a
few terms from her glossary. Cited as (from Herman). (Many
of these terms derived from the PPPL glossary I also used.)
! Paul M. Koloc, pmk@prometheus.UUCP - quality control, some entries
! Emilio Martines, martines@pdigi3.igi.pd.cnr.it - quality control,
reversed-field entries & information.
! Robert Nachtrieb, nachtrieb@pfc.mit.edu - numerous acronyms
* Princeton Plasma Physics Lab, Glossary of Fusion Terms - list of
terms prepared by PPPL staff at some point. Consulted in many
cases, blatantly paraphrased in some, quoted and cited in
others.
* Vicki Rosenzweig, vr%acmcr.uucp@murphy.com - Proofreading entries
* Mike Ross, mikeross@almaden.ibm.com - additional Livermore info
and corrections to some entries.
* Richard Schroeppel, rcs@cs.arizona.edu - suggestions/corrections to
many definitions.
! Philip Snyder, pbsnyder@theory.pppl.gov - corrections to
definitions.
! Paul Stek, Stek@cmod.pfc.mit.edu - additional definitions
!? Mitchell Swarz, mica@world.std.com - supplied additional
definitions / corrections and revisions to existing definitions.
* United States Department of Energy, Office of Fusion Energy -
for funding fusion research and making everything possible
* United States Department of Energy, Office of Scientific and
Technical Information - for the 1985 Glossary of Fusion Energy,
which I have utilized extensively and incorporated into this Glossary.
# This file may be freely distributed; I recommend you retain the
revision date, and in any case I'd like to be cited as the editor. #
# Any and all errors are solely my responsibility. #
#####################
Robert F. Heeter
rfheeter@pppl.gov
Graduate Student, Princeton Plasma Physics Lab
(Usual disclaimers apply.)
Subject: Conventional Fusion FAQ Glossary Part 11/26 (K)
From: Robert F. Heeter
Date: 23 Nov 1996 06:15:17 GMT
Archive-name: fusion-faq/glossary/k
Last-modified: 4-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 11: Terms beginning with "K"
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).
==================================================================
KKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKKK
# k: Mathematical symbol usually used for Boltzmann's Constant.
Value is 1.4 x 10^-23 Joules/Kelvin (in SI units),
or 1.4 x 10^-16 ergs/Kelvin (in cgs units).
$ kA: KiloAmpere; see kilo, Ampere
@ KDP: Potassium Dihydrogen Phosphate; crystal used in frequency
conversion of Nd:glass laser light.
$ kW: KiloWatt (1000 watts); see also kilo, Watt
$ kWh: kilowatt-hour; see entry
& Kelvin: (K) temperature scale where zero degrees corresponds
to absolute zero (no thermal energy); degrees have same
size as in Celsius/centigrade scale. 273.16 K = zero C;
373.16 = 100 C.
! (Lord) Kelvin: honorary name given to William Thompson; 19th
century British physicist (many contributions in many subfields).
* Kerma: Kinetic Energy (of charged particles) produced by
ionizing Radiation per unit MAss of irradiated material. (ergs/gm)
& kilo: metric prefix used to indicate 1000 times the following
unit. e.g., a kiloampere is 1000 amperes.
$ kilowatt-hour: standard unit of electrical energy; equals one
kilowatt of power delivered for one hour. Equivalent to 3.6
million joules.
* Kinetic Pressure: Density of kinetic energy (energy in the
thermal motions of the plasma particles). For an ideal plasma,
pressure is given by p = nkT, that is:
pressure = (density) * (Boltzmann's constant)* (temperature),
* Kinetic Temperature: A measure of the energy of random motion
(kinetic energy) of an assembly of particles in thermodynamic
equilibrium.
* Kinetic Theory: A theory which attempts to explain the behavior
of physical systems using the assumptions that the systems are
composed of large numbers of atoms/molecules/particles in
vigorous motion, that energy and momentum are conserved in
collisions of these particles, and that statistical methods can
be applied to deduce the behavior of such systems.
* Kink Instability: Instability resulting from excessive growth
of a kink mode; see kink mode.
* Kink Mode: Class of MHD instabilities which sometimes develop
in a thin plasma column carrying a strong axial current. If a
kink begins to develop in such a column the magnetic forces on
the inside of the kink become larger than those on the outside,
so that in general it tends to grow in magnitude. The column
then becomes unstable and can be displaced into the walls of
the discharge chamber, causing a disruption.
& Klystron: An evacuated electron-beam tube in which electrons
are given initial velocities such that the beam's charge density
is modulated; the passage of a modulated current generates
microwave radiation, some of which is then fed back to modulate the
electrons' velocities. The result is a microwave amplifier.
* Kruskal Limit: In tokamaks, a theoretical limiting value for
plasma current beyond which MHD instabilities are predicted.
