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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 4/26 (D)
- Supersedes: <fusion-faq/glossary/d_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:24:59 GMT
- Organization: Princeton University
- Lines: 303
- Approved: news-answers-request@MIT.EDU
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/d_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:44252 sci.answers:10849 news.answers:170835
-
- Archive-name: fusion-faq/glossary/d
- 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 4: Terms beginning with "D"
-
- 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
-
- The list of Acknowledgements is in Part 0 (intro).
- ==================================================================
-
- DDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDDD
-
- @ D: nuclear/chemical symbol for deuterium/deuteron
-
- @ DC, dc: Direct Current; see entry
-
- @ DCLC: Drift Cyclotron Loss Cone instabilities; see entry.
-
- @ DT: Deuterium-Tritium; see entry labeled DT Fuel
-
- @ DIII-D: not an acronym (anymore); see entry
-
- @ DOE: Department of Energy (United States); see entry
-
- @ dpa: Displacements per atom; see entry
-
- @ DPP: Division of Plasma Physics; see APS-DPP
-
- * D-shaped plasma: A toroidal plasma whose cross section
- (poloidal plane) is a D (instead of a circle). A D-shape
- has a higher beta limit (see entry) than a circular shape.
-
- * Debye Length: The characteristic distance over which charges are
- shielded in a plasma. See also: Debye shielding.
- lambda_D = ( epsilon_0 k_B T_e / (n_e e^2) )^(1/2)
- lambda_D[m] = (7.434*10^3)*(_e[eV])^(1/2)*n[m^(-3)]^(-1/2)
- (Arthur Carlson, awc@ipp-garching.mpg.de)
-
- ! Debye, Peter Joseph: Physical chemist, studied behavior of
- conductive solutions (plasmas have some similar behaviors).
-
- * Debye Radius: See Debye Length.
-
- * Debye Sheath: The region of strong electric field in front of
- a material surface in contact with a plasma. Its characteristic
- thickness is the Debye length, and it is caused by Debye shielding
- of the negative surface charge resulting from electrons flowing to
- the surface much faster (initially) than the ions. The lost
- electrons leave behind a region of net positive charge which
- gradually diminishes the strength of the electric field
- over the debye length. See also: Debye Length, Debye Shielding.
- (Arthur Carlson, awc@ipp-garching.mpg.de, with modifications by
- John Cobb, johncobb@uts.cc.utexas.edu)
-
- * Debye Shielding: If a positive (or negative) charge is inserted
- into a plasma, it will change the local charge distribution by
- attracting (repelling) electrons. The net result is an additional
- negative (positive) charge density which cancels the effect of the
- initial charge at distances large compared to the Debye length.
- (There is a corresponding effect of shielding by the ions, which,
- for various and subtle reasons, usually is less important.)
- See also: Debye Length.
- (Arthur Carlson, awc@ipp-garching.mpg.de)
-
- * Debye Sphere: Sphere around a charged test particle whose
- radius is equal to the Debye length.
-
- & Decay, Radioactive: See radioactive decay.
-
- * Decay Modes: Different pathways for decay of radioactive nuclei.
- The decay modes for a given unstable state can include beta
- emission (negative = electron, positive = positron), electron
- capture, alpha emission, fission, and gamma emission.
- (Did I miss any?) See entries for each mode for more information.
-
- * Dee-Shaped: see D-shaped plasma above.
-
- * Degenerate Configuration: Magnetic field configuration in
- which the magnetic lines of force close exactly on themselves
- after passing around the configuration a finite number of times.
-
- * Dense Plasma Focus: See Plasma Focus. (Densities of up
- to 10^26 particles/m^3 have been reported.)
-
- & Density: amount per unit of volume, or per unit surface area, or
- per unit length. (Usually specified or clear from context which
- of these is meant). Several types:
- Charge density - amount of charge per unit (volume, area, length)
- Current density - current flow per unit transverse surface area.
- Energy density - amount of energy per unit volume.
- Flux density - flux per unit of transverse surface area.
- Mass density - mass per unit volume.
- Number density - number of particles per unit volume.
- Particle density - same as number density.
-
- % Department of Energy: (DOE) Department within the
- executive branch of the U.S. government (at the cabinet
- level) which has managed and overseen federally-sponsored
- energy research. The DOE was formed in 1977 from ERDA,
- the Energy Research and Development Administration,
- and (I think) the Atomic Enegy Commission (AEC).
-
- & Deuterium: A heavy isotope of hydrogen whose nucleus
- contains both a neutron and a proton.
-
- * Deuteron: A deuterium ion; nucleus consisting of a proton
- and a neutron.
-
- * Diagnostics: (from Herman) Procedures for determining
- (diagnosing) the state of a plasma during an experiment;
- also refers to the instruments used for diagnosing.
-
- * Diamagnetic Effects: Application of a magnetic field to a plasma
- will tend to create circulating current within the plasma that will
- reduce the strength of the magnetic field.
-
- * Diffusion: The interpenetration of one substance into another
- as a result of thermal / random motion of the individual particles.
- (e.g., the diffusion of a plasma across a magnetic field as a
- result of collisions which cause particles to move along new
- field lines.) See also classical diffusion, neoclassical diffusion,
- anomalous diffusion, transport.
-
- * Direct Conversion: The generation of electricity by direct
- recovery of the kinetic energy of the charged fusion reaction
- products.
-
- & Direct Current: Electric current which is unchanging in
- time, or at least not oscillating. Opposite of Alternating Current.
-
- * Direct Drive: An approach to inertial-confinement fusion
- in which the energy of the driver (laser or particle beam)
- is directly incident on the (usually spherical) target,
- causing compression heating via ablation of the target surface.
-
- * Dispersion Relation: For a given wave, the dispersion relation
- relates the temporal frequency of a wave (w, or omega) to its
- wavenumber k and other physical quantities characteristic of
- the system. Dispersion relations can be quite simple
- (e.g., w = k * c for light; c being the speed of light),
- and they can also be quite complex, with interesting
- mathematical structure. The dispersion relation and its
- mathematical structure provide important information
- about the wave, including the phase and group velocities.
- (See relevant entries.) Note that the meaning of "dispersion
- relation" is different in plasma physics than in other fields.
-
- * Displacements Per Atom: (dpa) This is a measure of the
- amount of radiation damage in neutron-irradiated materials;
- e.g., 10 dpa means each atom in the material has been
- displaced from its structural lattice site and average of
- 10 times (due to interactions between the atoms and the
- energetic neutrons irradiating the material.)
-
- * Disruption: Plasma instabilities (usually oscillatory modes)
- sometimes grow and cause disruptions of the carefully-engineered
- plasma conditions in the reactor. Major disruptions can cause
- an abrupt temperature drop and the termination of the plasma.
- Stored energy in the plasma is rapidly dumped into the rest
- of the plasma system (vacuum vessel walls, magnet coils, etc.)
- and can cause significant damage if precautions are not taken.
-
- * Disruptive Instability: Instability which causes a disruption;
- see entry for disruption.
-
- * Dissociative Recombination: The combination of an electron
- with a positive molecular ion, followed by dissociation of
- the molecule in which the resulting atoms/molecules carry
- off the excess energy released in the recombination.
-
- & Distribution Function: Function characterizing the density of
- particles located at a given point in phase space (a combination
- of either velocity or position coordinates) at a given time.
- The velocity-space distribution function gives the number of
- particles with a particular velocity; the position-space
- distribution function is synonymous with the particle density
- in position-space. Different combinations of position and
- spatial coordinates are useful in different problems.
-
- * Divertor: Component of a toroidal fusion device that diverts
- charged particles on the outer edge of the plasma into
- a separate chamber where they strike a barrier and become
- neutralized. In a reactor, the divertor would incorporate a
- system for pumping out the neutralized particles as exhaust
- from the machine. A divertor, like a limiter, prevents the
- particles from striking and degrading the chamber walls
- and dislodging secondary particles that would cool and
- contaminate the plasma. Whereas a limiter is a material
- object used to limit the shape of the plasma, a divertor is a
- magnetic-field construction. The advantage of the divertor
- is that it allows the neutralization region to be
- removed from the main plasma. See also: limiter.
-
- * Doppler Broadening: Frequency spreading which causes
- broadening of single-frequency radiation (e.g., spectral
- lines) when the radiating bodies (atoms, molecules, etc.)
- have different velocities. Radiation from each individual
- radiating body has a different Doppler shift, and
- the collection of radiations at different frequencies
- broadens the peak of the line in an intensity-vs-frequency
- plot.
-
- & Doppler Effect: Variation in the frequency of a
- wave (as measured by an observer) due to relative motion
- between the observer and the source of the wave.
- (The observed frequency increases if the source is moving
- towards the observer.)
-
- & Doppler Shift: The amount of change in the observed
- frequency of a wave due to the Doppler effect; sometimes
- called the Doppler frequency.
-
- > DIII-D: Latest in a series of tokamaks designed
- by General Atomics (formerly GA Technologies) in San Diego
- making plasmas with noncircular cross sections, including
- kidney shapes and D-shapes.
-
- * Doublet Device / Doublet Plasma: Tokamak-type devices
- where the plasma cross-section is kidney-shaped, with
- a deep indentation in the middle so that the plasma has
- two major rings of current (on top and bottom).
-
- * Drift Cyclotron Loss Cone Instabilities: (DCLC)
- This is an electrostatic microinstability (frequencies
- at harmonics of the ion cyclotron frequency) which is of
- major concern in small mirror devices. Mode is driven
- by radial gradients in the electron density, and causes
- loss of ions due to non-conservation of magnetic moment
- (see adiabatic invariant) as they interact with the mode,
- and are dispersed in velocity space into the loss cone.
- Stabilization is accomplished by increasing the plasma
- size and by partially filling the loss cone with a
- continuous extermal warm plasma stream.
-
- * Drift Motion: Ordinarily particles placed in a magnetic
- field will simply orbit in circles, but if the magnetic field
- is not uniform, or curves, or there is an electrical field
- perpendicular to the magnetic field, or another force is applied
- perpendicular to the magnetic field, then the "guiding centers"
- of the particle orbits will drift (generally perpendicular to
- the magnetic field and to the applied force). There are several
- sorts of drifts; refer to a plasma physics text for more
- information (see Section 11: Bibliography). For a good
- introduction at the undergraduate physics level, see Chen.
-
- * Drift Pumping: A process that removes ions trapped in
- a thermal barrier using radial transport induced by an
- exterally-applied radiofrequency field tuned to resonate
- with the azimuthal drift frequency.
-
- * Drift Surface: Surface on which the guiding center of
- a particle is constrained to move, due to the effects of
- the laws of adiabatic invariance on its drift motion.
-
- * Drift Velocity: Characteristic velocity at which the center
- of a particle's orbit ("guiding center") drifts when drift motion
- (see above) occurs.
-
- * Drift Waves: Oscillations in a magnetically-confined plasma
- arising in the presence of density gradients (such as at the
- plasma's surface). These resemble the waves that propagate
- at the interface of two fluids with different density in
- a gravitational field.
-
- * DT Fuel: (Deuterium-Tritium) Easiest fuel mixture to use
- in achieving fusion; unless otherwise specified, probably refers
- to a 50-50 (by numbers or by moles) mix of deuterium and tritium.
-
- * Duty Factor: Ratio of the duration of time when a system is
- actually operating to the total time for a complete cycle
- of the system. e.g., if a tokamak experiment runs for 5 seconds
- and then sits for 500 seconds while the power supplies are
- recharged, then the duty factor is 1%. Similar to capacity
- factor for powerplants.
-
- * Dye laser: A type laser in which the active material
- (the material which emits the laser light) is a dye.
- These lasers are tunable when the dye has very large
- molecules (such as acridine red or esculin) and the laser
- action takes place between the first excited and ground
- electronic states, because each of these states contains
- a broad continuum band of vibrational-rotational levels.
-
-
-