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Conventional Fusion FAQ Glossary Part 5/26 (E)

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Archive-name: fusion-faq/glossary/e
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!!!).

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Glossary Part 5:  Terms beginning with "E"


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).


# e:  symbol for the electron, for the unit electric
      charge (e = 1.6x10^-19 coulombs), and for a Euler's fundamental
      mathematical constant e = 2.71828...

# E:  Variable typically used for Energy or Electric Field
(usually in vector notation in the latter case; which is meant
is usually clear from context; when both are used in the same place
the energy is usually represented as U instead of E.)

@ EBT:  Elmo Bumpy Torus; see entry

@ EC:  European Community; see entry

@ ECDC:  Electron Cyclotron Discharge Cleaning; see entry

@ ECE:  Electron Cyclotron Emission; see entry

@ ECH:  Electron Cyclotron Heating; see entry

@ ECRH:  Electron Cyclotron Resonance Heating - same as ECH.

@ EF:  Equilibrium (vertical) Field Electromagnet Coil; see vertical field

$ ECU:  European Currency Unit

@ ELM:  Edge-Localized Mode; see entry

@ EM:  Electromagnetic

@ EM Wave:  Electromagnetic Wave; see entry

@ EPA:  Environmental Protection Agency (U.S.); see entry

@ ERDA:  Energy Research and Development Agency; see entry

@ ESECOM:  Reactor design study done in the mid 1980s to
evaluate the Environmental, Safety, and ECOnoMic potential
of different types of fusion and advanced fission reactors.

@ ESNET:  Energy Sciences NETwork; no entry yet

@ ETF:  Engineering Test Facility

@ EU:  European Union; see entry

@ eV:  Electron-volt; see entry

$ Exa:  metric prefix for 10^18 or 1,000,000,000,000,000,000

$ Exajoule:  unit of energy, 10^18 joules; often used as unit
of measure for world annual energy use.  Comparable in size to
a Quad (1 EJ = 0.948 Quads); see entry for Quad.

* E-Coil:  The plasma current driving (Ohmic Heating) coil
in a Doublet device (see entry for doublet).  Ideally the
E-coil makes no magnetic field in the confinement system. (?)

* E-Layer:  Cylinder of relativistic electrons gyrating in
a magnetic field, which produce a self-field strong enough
to dominate the externally applied field and produce a
field-reversal (where the B field changes sign) in the
system.  See Field-Reversed Configuration, Field-Reversed Pinch.

* Echoes:  Wave packets (pulses) which have been reflected
or otherwise returned to the detector, which are sufficiently
delayed and retain sufficient magnitude so that they are
perceived as a signal distinct from the one transmitted
directly.  (In other words, just like sound echoes, only
for analogous phenomena with other waves.)

* Eddy Current:  Electric current induced inside a conductor
when the conductor (a) moves through a nonuniform magnetic
field, or (b) experiences a change in the magnetic flux
through its surface.

* Eddy-Current Loss:  Energy loss due to eddy currents
circulating in a resistive material.

* Edge Localized Mode: (ELM) Mode found often in H-mode plasmas.
This is a temporary relaxation of the very high edge gradients
found in H-modes. It may be a relaxation back to the L-mode.
(Borrowed from a posting by Paul Stek)

* Edge Plasma:  Cooler, less dense plasma away from the center
of a reactor; affected by limiter or divertor, includes
scrape-off layer.  Distinguished from core plasma.  See entries
for relevant terms used.

* Edge-Localized Mode:  (info from Paul Stek)  Found often in
H-mode plasmas, this is a temporary relaxation of the very high
edge gradients found in H-modes. It may be a relaxation back
to the L-mode.

* Effective Collision Cross-section: (See collision cross section)

* Effective Collision Radius:  Effective size of a particle
equal to the square root of (cross section/pi).  Determines the
effective range of interaction of the particle.

* Effective Half-Life:  Time required for a radioactive substance
contained in a biological system (such as a person or an animal)
to reduce its radioactivity by half, as a combination result
of radioactive decay and biological elimination from the system.

& Eigenfrequency:  One of the characteristic frequencies at
which an oscillatory system can vibrate.

& Eigenfunction:  Function describing an eigenstate of a

& Eigenstate:  One of the characteristic states of an
oscillatory system, such that the system does not leave the
state unless disturbed.  (?)

& Eigenvector:  Same thing as an eigenfunction, only from the
perspective that the eigenfunction is a "vector" in an
appropriate mathematical vectorspace.

* Eikonal Equation:  An equation for propagation of electromagnetic
or acoustic waves in an inhomogenous medium; valid only when the
scale length for variation in the properties of the medium is
small compared to a wavelength.  (Similar in character to WKB?)

& Elastic:  Term used to describe a process in which kinetic energy
is conserved; usually refers to (elastic) collisions or (elastic)

& Electric Charge:  See charge, electrical.

& Electric Field:  A property of a patch of space which causes
the acceleration of electric charges located at that patch of
space.  The acceleration is given by a = qE/m, where q is the
charge, E the electric field vector, and m the mass of the

% Electric Power Research Institute: (EPRI)  Research organization
funded by the electric power utilities to study, well, electric

* Electric Probe:  See Langmuir Probe.

& Electrical Conductivity:  Degree to which a substance conducts
electric current.  Can be defined by:
        (current density) = (conductivity) * (applied electric field)
Electrons and ions both contribute to current in proportion to
their mobility in the system.  In a plasma with a magnetic field,
there is no longer a one-to-one correspondence between current
and electric field.  Instead, the current in each direction can
be due to combinations of the electric fields in all the other
directions.  In this case, the current density and the
electric field are vectors, and the conductivity becomes a
tensor (matrix) which relates them.

* Electromagnetic Coupling:  A means of extracting energy from a
magnetically confined plasma, where the plasma expands and pushes
on the confining magnetic field, causing electrical energy to
be generated in the external field-generating circuits.

& Electromagnetic Force:

* Electromagnetic Radiation:  Radiation (such as radio waves,
microwaves, infrared, visible light, ultraviolet, x-rays, and
gamma rays) which consists of associated, interacting electric
and magnetic field waves which travel at the speed of light
(because electromagnetic radiation *is* light, except for the
variation in frequencies!).  All forms of electromagnetic
radiation can be transmitted through vacuum.  Electromagnetic
waves in plasmas are generally more complex in their behavior,
depending on their frequency.

& Electromagnetic Wave:  Wave characterized by combined oscillations
of both electric and magnetic fields.  The particle equivalent
is the photon.  There is a whole spectrum of electromagnetic
waves where the classes are distinguished by energy (or,
equivalently, wavelength or frequency); the spectrum of
electromagnetic waves includes radio waves, microwaves,
infrared light, visible light, ultraviolet light, x-rays, and
gamma rays.

& Electron:  Elementary particle with a negative electric
charge.  Electrons orbit around the positively charged nucleus
in an atom.  The charge on an electron is -1.6x10^-19 coulombs;
the electron has a mass of 9.11 x 10^-31 kg (about 1/1837
times that of a proton.)  The configuration of electrons around
an atom determines its chemical properties.  The positron
is the antiparticle to the electron, and is identical except
for having a positive charge.

> Electron Beam Fusion Accelerator:  See PBFA (Particle Beam
Fusion Accelerator)

* Electron Capture:  Nuclear decay process whereby a proton in
the nucleus absorbs an orbiting electron and converts to a

* Electron Cyclotron Discharge Cleaning: (ECDC)  Using relatively
low power microwaves (at the electron cyclotron frequency) to
create a weakly ionized, essentially unconfined hydrogen plasma
in the vacuum chamber.  The ions react with impurities on the
walls of the tokamak and help remove them from the chamber.  For
instance, Alcator C-mod typically applies ECDC for a few days
prior to beginning a campaign, and a few hours before each day's run.

* Electron Cyclotron Emission: (ECE)  As electrons gyrate around in
a magnetic field (see also larmor radius or cyclotron radius),
they radiate radio-frequency electromagnetic waves.  This is
known as electron cyclotron emission, and can be measured to
help diagnose a plasma.

* Electron Cyclotron Heating: (ECH or ECRH)  Radiofrequency
(RF) heating scheme that works by injecting electromagnetic (EM)
wave energy at the electron cyclotron gyration frequency.
The electric field of the EM wave at this frequency looks to
a gyrating electron like a static electric field, and it
causes acceleration of the electron.  The accelerated
electron gains energy, which is then shared with other particles
through collisions, resulting in heating.

* Electron Cyclotron Wave:  Radiofrequency waves at the
electron cyclotron frequency.  See also Whistler.

* Electron Density:  Number of electrons in a unit volume.
See density for more info.

* Electron Temperature:  The temperature corresponding to
the mean kinetic energy of the free electrons in a

$ Electron-volt: 1 eV = 1.6 x 10^-12 erg, or 1.6 x 10^-19 Joules.
This is a unit of kinetic energy equal to that of an electron
having a velocity of 5.93 x 10^5 m/sec.  This is the energy
an electron (or other particle of charge=1 such as a proton),
gains as it is accelerated through a potential difference
of 1 volt.  In plasma physics the eV is used as a unit of
temperature; when the mean particle energy is 1eV, the
temperature of the plasma is roughly 11,700 Kelvin.

* Electrostatic Analyzer:  A device which filters an
electrn beam (band-pass), permitting only electrons within
a narrow energy (velocity) range to pass.

> Electrostatic Confinement:  An approach to fusion based on
confining charged particles by means of electric fields, rather
than the magnetic fields used in magnetic confinement.  See
discussion in Section 4 for more information.

* Electrostatic Waves:  Longitudinal oscillations appearing in a
plasma due to a perturbation of electric neutrality.  For a cold
unmagnetized plasma, or at large wavelengths, the frequency of
these waves is by definition the plasma frequency.

& Element:  One of the fundamental chemical substances which
cannot be divided into simpler substances by chemical means.
Atoms with the same atomic number (# of protons) all belong
to the same element.  (e.g., hydrogen, helium, oxygen, lead)
(list and perhaps periodic table in
appendix?  isotope table with half-lives and decay modes
might also be useful.)

& Elementary Particles worth knowing about:
        (at the nuclear-energy level)
        electron & positron - seem to be stable
        proton - thought to be stable, life > 10^30 sec
        neutron - decays in ?10 min unless it's in a nucleus, which often
                extends its life.
        other particles important for nuclear energy:
                muon, neutrino (m,e,tau),
        muonic atoms
                this part is new - maybe separate entries with listing

> Elmo Bumpy Torus:  Bumpy Torus at ORNL; no longer operating.
See Bumpy Torus, ORNL.

* Elongation: parameter indicating the degree to which the cross
section of a toroidal plasma is non-circular. kappa=b/a, where "b"
and "a" are the vertical and horizontal minor radii. As kappa is
increased, the confinement in relation to the total current improves,
but the plasma also becomes more and more unstable to vertical
displacements. A circular plasma has kappa of 1, a common value for
elongated plasmas is 1.7, and the absolute limit is probably
around 2.

& Energy:  Typically defined as "the ability to do work".  Power
is the rate at which work is done, or the rate at which energy
is changed.  "Work" characterizes the degree to which the properties
of a substance are transformed.  Energy exists in many forms,
which can be converted from one to another in various ways.
Examples include:  gravitational energy, electrical energy,
magnetic and electric field energy, atomic binding energy (a form
of electrical energy really), nuclear binding energy, chemical
energy (another form of electrical energy), kinetic energy (energy
due to motion), thermal energy ("heat"; a form of kinetic energy
where the motion is due to thermal vibrations/motions), and so on.

* Energy Balance:  Comparison of energy put into a plasma with the
energy dissipated by the system; related to energy confinement.

* Energy Confinement Time:  See energy loss time.

* Energy Loss Time:  Characteristic time in which 1/e (or sometimes
1/2) of a system's energy is lost to its surroundings.  In a plasma
device, the energy loss time (or the energy confinement time) is
one of three critical parameters determining whether enough
fusion will occur.  (See Lawson criterion)

* Energy Replacement Time:  Time required for a plasma to lose
(via radiation or other loss mechanisms) an amount of energy
equal to its average kinetic energy.

% Energy Research and Development Agency (ERDA):  US Agency created
by splitting of the AEC into ERDA and NRC in about 1975, charged
with managing US energy R&D (???).  Merged with ??? to become the
Department of Energy in about 1977. (???? correct? help??)

* Entropy Trapping:  The process of trapping an ordered beam of
particles in a magnetic field configuration (e.g., cusp geometry)
by randomizing the ordered motion of the particles, with
corresponding increase in the entropy of the system.

% Environmental Protection Agency:  Agency within the executive
branch of the U.S. government (under the Department of the Interior?
Independent?) charged with, well, protection of the environment.
Activities include research, regulatory, and cleanup functions.
(Any government people reading this who could help me out?)

* Equations of Motion:  Set of equations describing the time
evolution of the variables which describe the state of a
physical system.

* Equilibrium:  [ acknowledgements to John Cobb ]  An equilibrium is
a state of a system where the critical parameters do not change
significantly, within a given time frame. In the case when this time
frame is infinite, It is called a Thermodynamic equilibrium. There
are many cases where a plasma equilibrium is constant on some fast
time scale, but changes over some slower time scale. For example, an
IDEAL MHD equilibrium is constant over fluid time scales
(microseconds to milliseconds), but it will evolve on the slower
resistive or viscous time scales (milliseconds to seconds). All
terrestial plasmas are NOT in thermodynamic equilibrium, but they may
be constant over very long time periods.

An equilibrium is unstable when a small change in a critical
parameter leads the state of the system to diverge from the
equilibrium.  An equilibrium is stable when a small change in a
critical parameter leads to a "restoring force" which tends to
return the system to equilibrium.

* Equilibrium Field:  See Vertical Field

$ Erg / ergs:  CGS unit for energy.  1E7 ergs = 1 joule.

* Ergodic:  A mathematical term meaning "space-filling".  If a
magnetic field is ergodic, any field line will eventually pass
arbitrarily close to any point in space.  Closely related to

* Ergodic Regime:  In this regime, a given magnetic field
line will cover every single point on a magnetic surface
(see magnetic surface or flux surface) if the rotational
transform (or q) is not rational.

* ESECOM:  Reactor design study done in the mid 1980s to
evaluate the Environmental, Safety, and ECOnoMic potential
of different types of fusion and advanced fission reactors.

* Eulerian Coordinates:  Coordinates which are fixed in
an inertial reference frame.

% European Community: see European Union

% European Union: (from Herman) Organization of European
countries (formerly European Community, EC, formerly European
Economic Community, EEC) established in 1967 to coordinate policies
on the economy, energy, agriculture, and other matters.  The original
member countries were France, Belgium, West Germany, Italy,
Luxembourg, and the Netherlands.  Joining later were Denmark,
Ireland, the United Kingdom, Greece, Spain, and Portugal.  Other
countries are in the process of joining now.

% Euratom:  European Atomic Energy Community.  International
organization established in 1958 by members of the European
Economic Community for the purpose of providing joint
funding and management of the scientific research of the
member countries - initially Belgium, France, Italy,
Holland, and West Germany.

* Excitation Radiation:  Line radiation (at characteristic
frequencies / wavelengths) as a result of the excitation
of excited states, and the subsequent de-excitation of
these states by radiative transitions.

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