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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 18/26 (R)
- Supersedes: <fusion-faq/glossary/r_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:26:11 GMT
- Organization: Princeton University
- Lines: 296
- Approved: news-answers-request@MIT.EDU
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/r_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 Glossary 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 Glossary does NOT
- discuss unconventional forms of fusion (like Cold Fusion).
- X-Last-Updated: 1995/02/26
- Originator: faqserv@penguin-lust.MIT.EDU
- Xref: senator-bedfellow.mit.edu sci.physics.fusion:44266 sci.answers:10863 news.answers:170849
-
- Archive-name: fusion-faq/glossary/r
- 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 18: Terms beginning with "R"
-
- 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).
- ==================================================================
-
- RRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRRR
-
- @ Rad: Radiation Absorbed Dose; see entry "rad"
-
- @ Rem: Raditation (or Roentgen) Equivalent for Man; see entry "rem"
-
- @ R&D: Research and Development.
-
- @ RD&D: Research, Development, and Demonstration.
-
- @ RF: Radio Frequency; see entry
-
- @ RF Current Drive: Radio Frequency Current Drive; see entry
-
- @ RF Heating: Radio Frequency Heating; see entry
-
- ! R.F. Heeter: Plasma physics graduate student at PPPL; the editor
- of the sci.physics.fusion FAQ, bibliography, and glossary. :)
- (note similarity to RF Heating.)
-
- @ RF Plugging: See entry for radiofrequency plugging
-
- @ RF Trapping: See entry for radiofrequency trapping
-
- @ RFC: Reversed-Field Configuration: see Field-Reversed Configuration.
-
- @ RFP: Reversed-Field Pinch; see entry
-
- @ RFX: Reversed-Field eXperiment; see entry
-
- @ RGA: Residual Gas Analyzer
-
- $ Rad: radiation absorbed dose. A unit used to measure the
- amount of radiation energy absorbed per gram of a given
- substance, that is the dose. One rad means absorption of
- 100 ergs of energy per gram. See also gray, rem, sievert.
-
- * Radial Ponderomotive Force Stabilization: In magnetic
- mirror devices, use of rf waves in the neighborhood of
- the ion cyclotron frequency to stabilize interchange
- modes. The radial ponderomotive force produced by
- a radial gradient in the applied rf electric field
- opposes the destabilizing centrifugal force resulting
- from bad magnetic field curvature. The net particle
- current is in the direction that would result from
- field lines with good curvature, eliminating the drive
- for the interchange instability.
-
- & Radiation: (Sense 1) Process of emission of energy from a body
- in the form of light or heat waves, or energetic particles
- such as alpha particles, electrons, or neutrons. (Sense 2)
- Radiation also refers to *what is emitted* when an object
- radiates (but not *what does the emitting*). A nucleus
- which does the emitting is said to be radioactive. Electrons
- in atoms can also emit radiation in the form of ordinary
- visible light; such atoms are not said to be radioactive.
-
- * Radiation Damage, Bulk: General term describing
- changes in chemical and/or metallurgical properties of
- structure components of fusion reactor caused by atomic
- displacement and nuclear transmutation events occuring
- as a result of exposure to a radiation environment
- (such as the neutrons emitted from a fission or D-T fusion
- reactor).
-
- * Radiation Damage, Surface: General term describing
- damage to the surface of the containment structure which
- directly interfaces with the thermonuclear plasma;
- includes such phenomena as radiation blistering,
- charged-particle (or neutron) sputtering, and spallation
- or exfoliation of layers of the surface.
-
- & Radioactive Decay: Spontaneous transformation of one
- nuclide into a different nuclide or into a different energy
- state of the same nuclide. This process results in a decrease,
- with time, in the number of originally radioactive atoms
- in a sample. See Decay Modes for a listing of the different
- mechanisms by which radioactive decay can occur.
-
- & Radioactive waste: Equipment and materials from nuclear
- operations which are radioactive and for which there is
- no further anticipated use. Wastes are generally classified
- as high-level (having radioactivity concentrations of
- hundreds to thousands of curies per gallon or cubic foot),
- low-level (in the range of 1 microcurie per gallon or
- cubic foot), or intermediate (between high and low).
- See also curie.
-
- & Radioactivity: Characteristic property of unstable nuclei
- which decay to other nuclei by emission of radiation. A list
- of common decay / transmutation modes is given under "decay
- modes".
-
- * Radio Frequency or radiofrequency: Term used to
- describe electromagnetic radiation with frequencies
- less than infrared, but greater than "audio frequencies,"
- i.e., greater than about 15,000 Hz. Wavelengths are
- therefore less than about 20,000 km and greater
- than about 0.01 mm. (These numbers are not precise.)
-
- * Radio Frequency Current Drive: Plasma waves in the
- radio-frequency range can be used to push plasma particles
- in such a way that current forms in the plasma; this is a
- method of non-inductive current drive (see entry) which
- would allow for steady-state fusion reactors to operate.
-
- * Radio Frequency Heating: Process for heating the plasma by
- transferring energy to ions or electrons using waves generated
- by an external oscillator at an appropriate frequency. (This is
- similar to how a microwave oven heats food.) There are various
- types: see also ECRH, ICRH, and Lower Hybrid...
-
- * Radiofrequency Plugging: Use of axial ponderomotive force
- to plug an open-ended device. First demonstrated on RFC-XX,
- Institute of Plasma Physics, Nagoya University, Nagoya, Japan,
- and later demonstrated in the Phaedrus device at the
- University of Wisconsin.
-
- * Radiofrequency Trapping: Use of RF waves to pitch angle
- scatter particles flowing axially into a magnetic mirror cell.
- The particles are scattered out of the loss cone and are
- trapped. (See entries for pitch angle scattering, magnetic
- mirror, loss cone.)
-
- * Railgun Accelerator: Projectile accelerator which
- accelerates the particle using electromagnetic forces which
- arise when the particle completes an electrical circuit between
- two conducting rails connected to a source of high current.
-
- * Raman Effect: A phenomenon observed in the scattering of
- light as it passes through a transparent medium; the light
- undergoes a change in frequency and a random alteration
- in phase due to a change in rotational or vibrational
- energy of the scattering molecules.
-
- * Ramsauer Effect: Term for a quantum-mechanical effect
- allowing free electrons within a narrow range of energies
- to pass through a noble gas with very little elastic scattering.
-
- * Rational Surface: (related to q-factor, see entry)
- Magnetic flux surface (see entry for this too) where the ratio
- of toroidal to poloidal field strengths is a rational number;
- this means that a particle travelling along this surface makes
- an integer number of turns in each direction and then its orbit
- closes in on itself. The result is that the particle doesn't
- sample the entire flux surface in its motion, which is important
- for various technical reasons (which mostly result in reduced
- confinement); see also magnetic island.
-
- * Reactor: See fission reactor, fusion reactor.
-
- & Recombination Coefficient: The rate of recombination of
- positive ions with electrons (or negative ions) in a gas,
- per unit volume, divided by the product of the particle
- densities of the two species (positive ions and
- electrons/negative ions) involved.
-
- * Recombination Radiation: radiation produced when a
- free electron in a plasma is captured by an ion.
-
- & Reflectivity: Fraction of incident radiant energy which
- is reflected by a given surface. (The power which is not
- reflected is either absorbed or transmitted.)
-
- & Refraction: Bending of waves as they pass from a medium
- having one refractive index to a medium (or region within
- a medium) having a different refractive index.
-
- $ Rem: Radiation (or Roentgen) Equivalent for Man. Unit of
- absorbed radiation dose based on the definition rem = rad * quality.
- The quality factor depends on the type of radiation involved and
- is used to scale the radiation dose based on the relative
- harmfulness of different sorts of radiation, compared to
- ordinary X-rays. Annual US average dose is about 300 millirem
- (0.3 rem), of which more than 2/3 is natural (primarily radon
- and cosmic rays), and the majority of the human-generated dose
- is due to medical uses (primarily X-rays). See also radiation
- dose, roentgen, sievert, rad, gray.
-
- * Reserves: Amount of a substance which can be extracted from
- the earth with current technology at current prices. Typically
- much smaller than resources (see entry for resources).
-
- & Resistance (electrical): Ability of a given object to
- resist the flow of electrical current. To drive a given
- current a voltage must be applied to overcome the resistance
- according to V = I * R (V = voltage, I = current, R = resistance).
- Resistance is determined by resistivity and geometrical factors.
-
- * Resistive Instability: Instability resulting from macroscopic
- equations used to model a plasma of finite conductivity / nonzero
- resistivity.
-
- & Resistivity: Tendency for a material/substance
- to resist the flow of electrical current and to dissipate its
- energy. Resistivity, when combined with certain geometry
- factors (generally length and cross-sectional area for wires)
- determines resistance.
-
- * Resource: Total amount of a substance which exists in the
- earth and could conceivably be extracted someday at some price
- with some technology. Typically much larger than reserves.
- (See also reserve.)
-
- > Reversed-Field Pinch (RFP): A toroidal magnetic confinement scheme
- which could constitute an alternative to the Tokamak for building a
- fusion reactor. It is characterized by a magnetic field mostly
- generated by the plasma itself, with toroidal and poloidal components
- of comparable intensities, in contrast with the Tokamak where most of
- the field is toroidal and externally applied. The name of the
- configuration is given by the fact that the toroidal component of the
- magnetic field changes sign in the outer region of the plasma. The
- main attractivness of the Reversed Field Pinch is that, according to
- presently established scalings, it could reach ignition without the
- need of auxiliary heating.
- (Emilio Martines, martines%pdigi3.igi.pd.cnr.it)
-
- > Reversed-Field eXperiment (RFX): It is the largest Reversed Field
- Pinch device presently in operation. Located in Padova (Italy) it
- is planned to reach a plasma current of 2 MA.
- (Emilio Martines, martines%pdigi3.igi.pd.cnr.it)
-
- * Roentgen: Unit of exposure to ionizing radiation. The Roentgen
- is that amount of gamma or X-rays (electromagnetic radiation)
- required to produce ions carrying one electrostatic unit of
- electrical charge (either positive or negative) in 1 cubic
- centimeter of dry air under standard conditions. Named after
- Wilhelm Roentgen. (Compare with curie, rad, gray, sievert.)
-
- ! Roentgen, Wilhelm: German scientist who discovered X rays in 1895.
-
- * Rogowski Loop or Coil: A coiled wire loop which encircles a
- current-carrying plasma. Changes in total plasma current induce a
- voltage in the loop; integrating (adding up) the voltage over time
- gives the plasma current.
-
- * Rotational Transform: (labels: \iota = 2*PI/q)
- Due to the combination of applied toroidal field and induced
- poloidal field, the magnetic field lines wind helically around
- the torus (and on most flux surfaces they fill the surface
- ergodically). The rotational transform is a measure of this
- helicity, and is defined as the average angle the field line
- shifts in the poloidal direction per complete circuit in the
- toroidal direction. The quantity q = 2*\pi / \iota is known
- as the ``safety factor'' because of its role in stability theory.
- (Contributed by James Crotinger)
-
- Entry from 1985 OSTI Glossary: A magnetic field configuration
- is said to posses rotational transform if the lines of force,
- after one complete circuit around the configuration (e.g., a torus)
- do not simply close exactly on themselves, but are instead
- rotated through some angle about the magnetic axies.
- (See entries for flux surface, magnetic axis, toroidal and poloidal
- field, helicity, safety factor.)
-
-
- * Runaway Electrons: Those electrons in a plasma that gain energy
- from an applied electrical field at a faster rate than they lose
- it through collisions with other particles. These electrons tend
- to "run away" in *energy* (not position) from the cooler remainder
- of the background plasma, because the collision cross-section
- decreases as the particle's velocity increases, so that the faster
- the particle goes, the less likely it is to be stopped.
- See also: collision cross-section.
-
-
-
-