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- Path: senator-bedfellow.mit.edu!faqserv
- From: Robert F. Heeter <rfheeter@princeton.edu>
- Newsgroups: sci.physics.fusion,sci.answers,news.answers
- Subject: Conventional Fusion FAQ Glossary Part 2/26 (B)
- Supersedes: <fusion-faq/glossary/b_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:24:51 GMT
- Organization: Princeton University
- Lines: 365
- Approved: news-answers-request@MIT.EDU
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/b_942323057@rtfm.mit.edu>
- References: <fusion-faq/glossary/intro_942323057@rtfm.mit.edu>
- Reply-To: rfheeter@pppl.gov
- NNTP-Posting-Host: penguin-lust.mit.edu
- Summary: Fusion energy represents a promising alternative to
- fossil fuels and nuclear fission for world energy
- production. This FUT is a compendium of Frequently Used
- Terms in plasma physics and fusion energy research. Refer
- to the FAQ on Conventional Fusion for more detailed info
- about topics in fusion research. This FUT does NOT
- discuss unconventional forms of fusion (like Cold Fusion).
- X-Last-Updated: 1995/02/05
- Originator: faqserv@penguin-lust.MIT.EDU
- Xref: senator-bedfellow.mit.edu sci.physics.fusion:44250 sci.answers:10847 news.answers:170833
-
- Archive-name: fusion-faq/glossary/b
- 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 2: Terms beginning with "B"
-
- 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
-
- Citations and Acknowledgements appear in Section 11 of the FAQ.
-
- ==================================================================
-
- BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB
-
- # B: variable used for Magnetic Field
-
- # B: chemical symbol for the element boron; see entry
-
- # Be: chemical symbol for the element beryllium; see entry
-
- @ BCSS: Blanket Comparison and Selection Study (no entry)
-
- @ BHP: Biological Hazard Potential; see entry
-
- @ BPX: Burning Plasma eXperiment; see entry
-
- @ BTU: British Thermal Unit; see entry
-
- @ BWR: Boiling Water Reactor (fission); see entry
-
- * Background Radiation: Level of environmental radation due to
- "background" sources. Background sources can be natural, such
- as cosmic rays and natural radioactive elements (principally
- radon, but including other elements such as isotopes of potassium
- (which people get substantial amounts of in foods like bananas)).
- They can also be man-made, such as from fossil-fuel combustion,
- everyday leakage from nuclear activities, and leftover from
- atmospheric nuclear weapons tests. Background radiation is
- usually distinguished from acute radiation, such as from medical
- x-rays, nuclear accidents, radioisotope therapy, or other short-term
- doses. The man-made contribution to background radiation is
- quite small compared to the natural contribution; medical uses
- dominate human exposure to acute radiation.
-
- & Backscattering: Deflection of incident particle / radiation
- through an angle greater than 90 degrees relative to the original
- direction of motion/propagation.
-
- * Ballooning Instability: See Ballooning Mode
-
- * Ballooning Mode: A mode which is localized in regions of
- unfavorable magnetic field curvature ("bad curvature") and
- which becomes unstable when the force due to pressure
- gradients (grad p) is greater than the mean magnetic
- pressure force (grad B^2)/(8*pi).
-
- * Banana Orbit: The fast spiraling of an charged particle around a
- magnetic field line is accompanied by a slow movement ("drift") of
- the center of the sprial. Projected onto a poloidal plane, the drift
- orbit has the shape of a banana. These orbits are responsible for
- neo-classical diffusion (see entry).
-
- $ Barn: Unit of area equal to 1x10^-24 square centimeters
- (or 1x10^-28 square meters). Commonly used in describing
- cross sections of atomic, nuclear, and particle interactions.
- (see cross section).
-
- * Baseball Coils: Used in magnetic-mirror geometries to
- produce a minimum-B configuration; so-called because of their
- resemblance to the characteristic shape of lacing on a baseball.
-
- * Beam: stream of particles or electromagnetic radiation
- travelling in a single direction.
-
- * Beam-Beam Reaction: Fusion reaction which occurs from the
- collision of two fast ions originating in injected neutral beams.
-
- * Beam Dump: A mass of shielding material which absorbs
- the energy of a beam of particles or electromagnetic radiation.
-
- * Beam-Plasma Reaction: Fusion reaction which occurs from the
- collision of a fast beam ion with a thermal plasma ion.
-
- * Beam Splitter: Optical device for dividing a beam of
- electromagnetic radiation into two or more separate beams.
-
- * Beam-Wall Reaction: Fusion reaction which occurs from the
- collision of a fast beam ion with an ion embedded in or adsorbed
- onto the reactor wall.
-
- * Bean-Shaped Plasma: A toroidal plasma indented on the inboard
- side (that is, on the side with the "donut hole"); results in
- additional stability to ballooning modes (see entry). Moderate
- indentation (does, can, may?) provide access to the
- second-stability region (high beta). (see relevant entries)
-
- ! Becquerel, Antoine-Henri: French scientist and discoverer of
- radioactivity; co-winner of Nobel Prize. (See Curie)
-
- $ Becquerel: Unit of radioactivity equal to 1 disintegration per
- second. (see Curie)
-
- * Bellows: Flexible mechanical structure with walls like those
- of an accordion.
-
- * Bernstein Mode: Type of mode which propagates perpendicular
- to the equilibrium magnetic field in a hot plasma. The waves
- have their electric field nearly parallel to the wave propagation
- vector (nearly longitudinal). The modes propagate in
- frequency ranges lying between integer harmonics of the
- electron cyclotron frequency. Named after Ira Bernstein.
-
- & Beryllium: (Be) Element with atomic number 4 (four protons).
- May be useful in multiplying fusion neutrons to enhance tritium
- production in a lithium blanket; rather hazardous to handle.
- (See relevant terms mentioned.)
-
- * Beta, or beta-value: Ratio between plasma kinetic pressure and
- magnetic-field pressure; proportional to the ratio between plasma
- kinetic energy density and magnetic field energy density. Beta
- is usually measured relative to the total, local field
- (loosely called beta toroidal), but sometimes the plasma pressure
- relative to only the poloidal component of the field (beta poloidal)
- or relative to some external field (like the maximum field at the
- magnetic coils) is more useful. There is also a normalized beta
- (beta_N) of interest when discussing the beta limit (see entry).
- (lots of help from Art Carlson with the above.)
-
- "Because the cost of a reactor is strongly influenced by the
- strength of the magnetic field that must be provided, beta values
- are directly related to the economics of fusion power production.
- Beta is usually expressed as a percentage, with 5% generally
- believed to be the minimum value required for an economical
- fusion reactor." - from the PPPL WWW page on PBX-M.
- See also: pressure, kinetic pressure, magnetic pressure,
- second stability.
-
-
- * Beta-Normal: Beta-N, the normalized beta, is beta relative to
- the beta limit (see below).
-
- * Beta-Poloidal: Beta-P is the same as the ordinary beta, except
- only the poloidal field is used in calculating the magnetic field
- pressure. Beta-P is > 1 in many modern tokamaks.
-
- * Beta Emission: Form of nuclear decay where a neutron splits
- into a proton plus electron plus neutrino set. The proton
- stays in the nucleus but the electron ("beta ray") is ejected.
-
- * Beta Limit, also called Troyon Limit: If the plasma pressure in
- a tokamak becomes too high, the so-called ballooning modes become
- unstable and lead to a loss of confinement (sometimes catastophic,
- sometimes not). The exact value at which this occurs depends
- strongly on the magnetic field B, the plasma minor radius a, and
- the toroidal plasma current I, such that maximum value of the
- normalized beta, beta_N=beta*B*a/I, is around 4% (with B in Teslas,
- a in meters, and I in Mega-amperes). The exact value depends on
- details of the plasma shape, the plasma profiles, and the safety
- factor. (Beta entries provided by Art Carlson.)
-
- * Beta Particle / Beta Ray: Original term used for electrons
- (and positrons) ejected from decaying nuclei via beta emission.
- (Label derives from the old days when we had various kinds of
- radiation emission, and they were labeled alpha, beta, and
- gamma (the first letters of the Greek Alphabet) because no one
- really knew what any of them were.)
-
- * Beta value: See "beta" just above.
-
- * Biasing: [from Art Carlson] The vacuum vessel of a tokamak
- (or other device) has a variety of structures--limiters, divertor
- plates, the wall itself. These are usually mechanically and
- electrically connected, but it is possible to bias (charge) them to
- different voltages relative to each other. This allows some control
- over the electric fields and currents around the plasma, which can
- influence, for example, the thickness of the scrape-off-layer, the
- transition between L- and H-mode, and the equilibrium configuration.
- Biasing experiments are being done on DIII-D, TEXTOR, and TdeV.
-
- * Binary Collisions: Collisions involving only two particles;
- multiparticle collisions (eg, three-body collisions) are usually
- neglected/approximated...
-
- * Binding Energy: Energy required to separate two objects;
- conversely, energy released when two objects are allow to bind
- together. Equivalent to the mass defect (see entry) via E=mc^2.
-
- * Biological Hazard Potential (BHP): Measure of the hazard posed by
- a given quantity of radioactive material in which the variation in
- biological effects of the various elements are accounted for.
- (See also integrated biological hazard potential, IBHP)
-
- & Biot-Savart Law: General formula for determining the magnetic
- field due to a steady line (not space) current. Related to Ampere's
- Law.
-
- * Blanket: a region surrounding a fusion reactor core within
- which the fusion neutrons (if any) are slowed down, heat
- is transferred to a primary coolant, and tritium is bred
- from lithium (if tritium is used as fuel). In hybrid
- applications, fertile materials (U-238 or Th-232) are located
- in the blanket for conversion into fissile fuels.
-
- * Bohm diffusion: A rapid loss of plasma across magnetic field
- lines caused by microinstabilities. Theory formulated by the
- physicist David Bohm. From Chen's book
- (see bibliography): "Semiempirical formula for the diffusion
- coefficient given by Bohm in 1946 (noted by Bohm, Burhop, and
- Massey, who were developing a magnetic arc for use in uranium
- isotope separation)." Bohm diffusion was proposed (not derived
- from first principles) to scale as 1/B rather than the 1/B^2
- scaling predicted by classical diffusion. A 1/B scaling results
- from assuming that particles diffuse across field lines at an
- optimum rate (effective collision frequency=cyclotron frequency).
- The 1/B scaling is observed (approximately) in most reactors.
- (Acknowledgements to Philip Snyder) See also: diffusion,
- microinstabilities, field lines...
-
- * Boiling Water Reactor (BWR): Class of fission reactor where
- water is used as a coolant and allowed to boil into steam.
- (I don't remember much more about it - any help out there?)
-
- & Boltzmann constant: k = 1.38 x 10^-16 erg/degree. This
- is the ratio of the universal gas constant to Avogadro's number.
- It is also used to relate temperatures (Kelvin) to energies (ergs
- or Joules) via E = (constant of order unity) * kT.
-
- & Boltzmann Distribution: See Maxwell-Boltzmann distribution;
- distribution function.
-
- * Boltzmann Equation: Fundamental equation in kinetic theory
- which describes the evolution of the distribution function.
- (See also Vlasov equation.)
-
- * Bootstrap Current: Currents driven in toroidal devices by
- neo-classical diffusion (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.
-
- & Boron: (B) Fifth element (Z=5) in the periodic table; has
- 5 protons; potential use as an aneutronic fuel. (See FAQ section
- 1, part on reactions.) Also useful as a neutron-absorber.
-
- * Boronization: Energy confinement in a fusion plasma depends
- strongly on the average atomic number (Z) of the elements in the
- plasma. Boronization refers to a process whereby boron (atomic
- number 5) is injected into a plasma and used to coat the walls
- of the reactor; the effect is that impurities from the reactor
- walls which enter the fusion plasma are primarily boron (which
- has a fairly low Z) rather than the higher-atomic-number metals
- typically used in reactor structures. Boronization has been
- associated with improved fusion plasma performance. Boronization
- is an example of Wall Conditioning. See also Boron, atomic number,
- wall conditioning, impurities.
-
- * Bounce Frequency: 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).
-
- * Boundary Layer: In fluid flow, a narrow region next to a
- fixed boundary or surface where the fluid velocity rapidly
- changes from zero to some finite value. The term has been
- generalized to situations with similar mathematics.
-
- * Branching Ratio: In a fusion reaction involving two nuclei,
- there are typically a variety of possible sets of products which
- can form. The branching ratio for a particular set of products
- is the probability that that set of products will be produced.
-
- * Breakeven: there are several types:
- Commercial: When fusion power can be converted into enough
- electric power to power the reactor and generate enough
- electricity to cover the costs of the plant at economically
- competitive rates. (?)
- Engineering: When enough energy can be generated from the
- fusion power output to supply power for the reactor and
- generate a surplus; sort of commercial breakeven without
- the economic considerations. (?)
- Scientific: When fusion power = input power; Q=1.
- (See also Lawson Criterion)
- Extrapolated - projected for actual reactor fuel using
- an alternative fuel.
- Actual - determined using the actual fusion fuel to be
- used in the reactor (typically DT).
-
- * Breeder Material: In D-T fusion, refers to lithium or
- lithium-containing substances which are placed in the
- blanket to convert the fusion neutrons back into tritium,
- using nuclear transmutation of lithium isotopes.
-
- * Breeder Reactor: Class of nuclear reactor (could be fission
- or fusion) which uses some of the nuclear byproducts (generally
- neutrons) to transmute non-fuel materials to new materials which
- can be used for fuel in other reactors, in such a way that
- the reactor creates more fuel than it consumes (breeding).
- Term usually refers to reactors which breed fission fuel.
- Use of breeder reactors would greatly extend the fuel supply for
- nuclear fission energy, but also creates additional opportunities
- for diversion of fissile materials to weapons production and
- could exacerbate proliferation of nuclear weapons.
-
- & Bremsstrahlung: (German for "Braking Radiation") Electromagnetic
- radiation from a charged particle as it slows down (decelerates),
- or as it changes direction due to near collisions with other particles.
- Similar to synchrotron radiation (see also). In a plasma
- bremsstrahlung occurs when electrons (which are lighter and generally
- move faster) collide with ions (which are heavier and generally move
- slower); the acceleration/deceleration of the electrons causes them
- to radiate bremsstrahlung.
-
- & Brewster's Angle: The angle of incidence at which
- electromagnetic waves reflected from a dielectric medium are
- completely polarized perpendicular to the plane of incidence;
- the component polarized parallel to the plane of incidence is
- completely transmitted.
-
- * British Thermal Unit: Unit of energy needed to raise a pound of
- water by one degree fahrenheit; equal to 252 calories or 1055 Joules.
- (See also calorie, joule). Not part of the metric system.
-
- > Bumpy Torus: I believe this concept tries to combine mirror
- concepts with toroidal ones. My understanding is that it is
- essentially a series of mirrors stuck end to end and bent into
- a ring. - Albert Chou (corrections / enhancements welcome!)
-
- * Bunching: A technique for spatial compression of a pulse
- in a beam of charged particles.
-
- * Bundle Divertor: Divertor concept where a toroidal field
- coil extracts a "bundle" of toroidal field lines (flux) and
- forms a separatrix in the toroidal field. (Hard to do
- and tends to mess up axisymmetry of the torus; not used much.)
-
- > Burning Plasma eXperiment (BPX): Proposed U.S. successor to TFTR;
- never funded. See also: CIT, TPX.
-
- * Burnout: Rapid reduction in the neutral particle density
- in a plasma discharge; occurs when the ionization rate (which
- converts neutrals to ions and electrons) exceeds the rate
- of recombination (which converts ions to neutrals) and the
- rate of influx of neutral particles.
-
-
-