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Conventional Fusion FAQ Glossary Part 20/26 (T)

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Archive-name: fusion-faq/glossary/t
Last-modified: 25-Feb-1995
Posting-frequency: More-or-less-quarterly
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Glossary Part 20:  Terms beginning with "T"


Edited by Robert F. Heeter,

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).


# 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, 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

* 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,
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.    
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 

-> (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.

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