Edited by : M. A. Razzak, Graduate Student, Takamura Lab, Graduate School of Engineering (Nagoya University)
local instability which can develop in the TOKAMAK when the plasma
pressure exceeds a critical value; it therefore constrains the maximum
beta that can be achieved. It is analogous to the unstable bulge which
develops on an over-inflated pneumatic inner tube. See resistive
A plasma mode, which is localized
in regions of unfavorable magnetic field curvature (also known as
"bad curvature") that becomes unstable (grows in amplitude) when
the force due to plasma pressure gradients is greater than the mean
magnetic pressure force.
In a toroidal geometry, the
‘fast’ spiraling of a charged particle around a magnetic field line is
accompanied by a ‘slow’ drift motion of the particle’s center around
the spiral. When projected onto the poloidal plane of a toroidally
confined plasma, the drift orbit has the shape of a banana. These orbits
are responsible for neo-classical diffusion and for bootstrap current.
Also see trapping.
viewed from the Earth, the heliographic latitude of the center of the
solar disk. The center of the solar disk usually does not coincide with
the heliographic equator, due to a tilt of the solar axis with respect to
the ecliptic. (See Bo under solar coordinates.)
Bartels' rotation number
serial number assigned to 27-day rotation periods of solar and geophysical
parameters. Rotation 1 in this sequence was assigned arbitrarily by
Bartels to begin in January 1833, and the count has continued by 27-day
intervals to the present. (For example, rotation 2000 began on 12 November
1979, rotation 2030 on 30 January 1982.) The 27-day period was selected
empirically from the observed recurrence of geomagnetic activity
attributed to co-rotating features on the Sun. The Sun has an average
rotation period (as seen from the Earth) of 27.27 days; therefore, solar
longitude slowly drifts with respect to the Bartels rate. Compare
Coils (copper or super conducting)
that carry electrical current for producing magnetic fields that are
shaped like the seams of a baseball, also known as yin-yang coils.
Fusion reaction that occurs in
neutral beam heated plasmas from the collision of two fast ions
originating in the neutral beams injected into the plasma for heating
purposes. Distinguished from beam-plasma, beam-wall, and thermonuclear
Fusion reaction that occurs in
neutral-beam heated plasmas from the collision of a fast beam ion with a
thermal plasma ion.
Fusion reaction that occurs in
neutral beam heated plasmas from the collision of a fast beam ion with an
ion embedded in the plasma vacuum wall.
Type of plasma mode that
propagates perpendicular to the equilibrium magnetic field in a plasma.
Bernstein waves, named after the plasma physicist, Ira Bernstein, have
their electric field nearly parallel to the wave propagation vector and
their frequency between harmonics of the electron cyclotron frequency.
b = p/(B2/2mo). The
ratio of plasma gas pressure (p) to magnetic field pressure (B2/2mo) in a
TOKAMAK. p is the gas
pressure in Pascals (Newton/meter2), B is the magnetic field strength in
Tesla, and mo = 4p x 10-7 Henry/meter.
Ratio of plasma pressure to magnetic field pressure. One of the
figures of merit for magnetic confinement: the magnitude of the magnetic
field pressure is determined by the expenditure on the field coils, etc.,
that generate it; since fusion reactivity increases with plasma pressure,
a high value of beta is an indicator of good performance. The highest
value of beta achieved in a large TOKAMAK is about 13%, though much higher
values are theoretically possible at low aspect ratio and have been
achieved on START.
Maximum beta attainable, usually due to a deterioration in
the confinement. The Troyon beta limit, which states that beta (in
percent) cannot exceed g.I / a.B is often quoted. Here, g is the so-called
Troyon coefficient, and has an value of around 3.5 for conventional
TOKAMAKs. (I is the plasma current in MegaAmps, a is the minor radius in
metres, and B is the toroidal field in Tesla.) The normalised beta is
given by beta.a.B / I, and (when quoted in percent) cannot exceed g.
Also known as the Troyon Limit in a tokamak, the beta limit is the
maximum achievable ratio (beta, or beta value) of plasma pressure to
magnetic pressure for a given plasma to remain stable. In a tokamak, if
the beta value is too high, ballooning modes become unstable and lead to a
loss of plasma confinement.
electron emitted from the nucleus of a radioactive element and denoted by
the Greek letter, beta (b).
Beta, beta value
Ratio of plasma kinetic pressure
to magnetic field pressure. Beta is usually measured relative to the
total, local magnetic field but in some cases can be measured relative to
components of the total field, such as the poloidal field in tokamaks.
nuclear reactions, the energy associated with removing protons and/or
neutrons from the nucleus; in standard chemistry, it is the energy
associated with electronic bond making and breaking.
Bipolar magnetic region
region of the solar photosphere containing at least two areas of enhanced
magnetic fields of opposing polarity.
currents linking the Earth's ionosphere with more distant regions, flowing
along magnetic field lines. Named for Kristian Birkeland, a pioneer of
auroral research who first proposed such currents around 1900, these
currents are often associated with the polar aurora.
temperature of an object if it is reradiating all the thermal energy that
has been added to it; if an object is not a blackbody radiator, it will
not reradiate all the excess heat and the leftover will go toward
increasing its temperature.
The physical system surrounding the hot plasma that provides
shielding and absorbs fast neutrons, converts the energy into heat, and
produces tritium. Blanket
technology for the practical application of harnessing fusion energy is
still under development. The ultimate design may include a liquid metal
such as molten lithium, which produces tritium when it captures neutrons.
In a fusion power plant using deuterium-tritium fuel, the system
surrounding the plasma vessel used to slow down the neutrons produced, so
that the heat released can be used for electricity generation. In many
designs, the blanket is also used to synthesise tritium (from the neutrons
and a lithium compound) to use as fuel. See breeder.
A rapid loss of plasma particles
across magnetic field lines caused by plasma microinstabilities that
scales inversely with the magnetic field strength, unlike classical
diffusion that scales inversely as the square of the magnetic field
strength. Named after the plasma physicist David Bohm who first proposed
transport is the anomalous diffusion associated with long wavelength
plasma fluctuations and has the consequence that confinement times
increase linearly with magnetic field. In gyro-Bohm transport,
fluctuations have a shorter scale length, comparable with the ion
gyro-radius, and consequently the confinement time increases quadratically
with magnetic field. Gyro-Bohm transport is therefore more optimistic than
Bohm for large scale devices like ITER.
internal electronic energy changes of an atom are connected to the
frequency of the corresponding emitted radiation by the formula ε=h.ν,
with h the Planck constant. Usually, this equation is assumed to determine
uniquely the resulting intensity of the radiation. However, there is
theoretical and observational evidence that this assumption is only valid
if the broadening of the spectral line due to plasma field fluctuations
(Stark broadening) is small compared to the natural broadening. In
general, one has to assume a relationship in the form εrad=(1+Δνm,nD/Ai,k).h.ν
, where Δνm,nD is the dynamical Stark
Broadening due to the plasma field fluctuations and Am,n
the Atomic Decay Probability (natural broadening).
This could for instance resolve the discrepancy if one wants to explain
the radiative energy output of the present day sun solely through the
gravitational contraction of an initial gas cloud (see http://www.plasmafacts.de/index.html#A5).
Physics proves that in thermodynamic equilibrium (i.e. in a collisionally
determined closed system) the volume density of particles decreases
exponentially with increasing energy,i.e. f(ε)=
energy distribution of electrons within an atom is generally assumed to
behave in this way.
a generalized form of the Continuity Equation, the Boltzmann equation
constitutes an exact description for the density of a plasma constituent
both in real and velocity space. It can be written as
+v.gradr(n(r,v,t)) +F/M.gradv(n(r,v,t)) = qIon(r,v,t) +lRec(r,v,t) +C(r,v,t)
left-hand side of the equation describes the production and loss rates for
the density distribution function n(r,v,t) due to convection (transport) in geometrical and velocity
space (where F contains all
external forces on the particle with mass M, i.e. electric, magnetic and
gravitational forces), whereas the right-hand side contains the local
production and loss rates due to ionization (qIon),
and velocity changing collisions (C).
steady-state (time independent) equation for is given by setting
The ionization and recombination terms are usually neglected in standard
treatments. However, they are vitally important as they are responsible
for the inhomogeneities of the plasma density and affect therefore the
velocity distribution function through the convection terms in the
equation (see link below). Also, one should note that the usual
formulation in terms of the normalized distribution function f(r,v,t)= n(r,v,t)/N(r,t) (with N(r,t) =
∫d3v n(r,v,t) ) is in general not sufficient because of the dependence of
N(r,t) on r. For the one-dimensional case, the Boltzmann equation can be
written as a first order linear differential equation in either the
spatial or velocity variable. Formal solution yields a non-linear integral
equation which can then be solved numerically. (see http://www.plasmafacts.de/index.html#A6
for an application to ion diffusion in the earth's ionosphere).
Currents driven in toroidal devices by neo-classical processes (see
entry). They may amount to a substantial fraction of the net current in a
tokamak reactor, thus lengthening the pulse time or decreasing the power
needed for current drive.
Theory predicted in 1970 that a toroidal electric current will flow
in a TOKAMAK which is fuelled by energy and particle sources that replace
diffusive losses. This diffusion driven bootstrap current, which is
proportional to beta and flows even in the absence of an applied voltage,
could be used to provide the confining magnetic field: hence the concept
of a bootstrap TOKAMAK, which has no toroidal voltage. A bootstrap current
consistent with theory was observed many years later on JET and TFTR; it
now plays a role in design of experiments and power plants (especially
The average frequency of
oscillation of a particle trapped in a magnetic mirror as it bounces back
and forth between its "turning points" in regions of high
magnetic field. (See also trapped particle, turning points, banana orbit).
A collisional shock wave in front of the magnetosphere arising from
the interaction of the supersonic solar wind with earth's magnetic field.
A collisionless shock wave in front of a planetary magnetosphere;
the place where the supersonic flow of the solar wind is slowed to
subsonic speed by the planetary magnetic field.
A sharp front formed in the solar wind ahead of the magnetosphere,
marked with a sudden slowing-down of the flow near Earth. It is quite
similar to the shock forming ahead of the wing of a supersonic airplane.
After passing near Earth, the slowed-down flow gains speed again, to the
same value as the surrounding solar wind.
condition in which the fusion power produced by the plasma equals the
heating power put into the plasma. For a fusion power reactor to be
economically useful, a burning plasma must produce much more fusion power
than it consumes, thereby significantly exceeding the breakeven point.
engineering, scientific, and extrapolated)
Commercial Breakeven is when sufficient fusion power can be
converted into electric power to cover the costs of the fusion power plant
at economically competitive rates.
Engineering Breakeven is when sufficient electrical power can be
generated from the fusion power output to supply power for the plasma
reactor plus a net surplus without the economic considerations.
Scientific Breakeven is when the fusion power is equal to input
power; i.e. Q=1. (See also Lawson Criterion).
Extrapolated Breakeven is when scientific breakeven is projected
for actual reactor fuel (e.g., deuterium and tritium) from experimental
results using an alternative fuel (e.g., deuterium only) by scaling the
reaction rates for the two fuels.
term sometimes used to indicate that component of a fusion power plant
used to "breed", or produce via nuclear reactions, tritium from
the energetic neutrons released, for use as fuel in the power plant. The
most commonly used reaction is:-?
Occurs in plasma when electrons
interact (‘collide’) with the Coulomb fields of ions; the resulting
deflection of the electrons causes them to radiate.
ignited plasma is said to be "burning".
transient enhancement of the solar radio emission, usually associated with
an active region or flare.
plot of observed solar active region latitudes vs. time. This diagram,
which resembles a butterfly, shows that the average latitude of active
region formation drifts from high to low latitudes during a sunspot cycle.