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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 7/26 (G)
- Supersedes: <fusion-faq/glossary/g_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:25:22 GMT
- Organization: Princeton University
- Lines: 190
- Approved: news-answers-request@MIT.EDU
- Distribution: world
- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/g_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:44255 sci.answers:10852 news.answers:170838
-
- Archive-name: fusion-faq/glossary/g
- 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 7: Terms beginning with "G"
-
- 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).
- ==================================================================
-
- GGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGGG
-
- $ G: abbreviation for Gauss; see entry
-
- @ GA: General Atomic; see entry.
-
- @ GDC: Glow Discharge Cleaning; see entry.
-
- @ GN2: Gaseous diatomic Nitrogen (N2)
-
- @ GNP: Gross National Product; see entry.
-
- @ GW: Gigawatt; see entry
-
- @ GWe: Gigawatt - electrical energy; see gigawatt
-
- @ GWt: Gigawatt - thermal energy; see gigawatt
-
- & Gain: (Amplification) Increase in a signal transmitted
- from one point to another through an amplifier.
-
- # gamma: Third letter in the Greek alphabet; variable used for
- a number of things in phyics; in plasma physics gamma is often
- used as the variable for growth rates of instabilities.
-
- * Gamma Emission: Nuclear decay process whereby the nucleus goes
- from an excited state to a more stable state by emitting a gamma
- ray. (See entry for gamma ray.)
-
- * Gamma Rays: Electromagnetic radiation (photons) with energies
- greater than (roughly) 100 keV (that is, 100,000 electron volts).
- Gamma radiation frequently accompanies alpha and beta decays,
- and always accompanies fission. Gamma rays are highly penetrating
- and are best shielded against using dense materials, such as
- lead or depleted uranium. (Gamma rays are similar to X-rays, but
- are generally higher in energy and nuclear in origin.) See
- relevant entries for more info.
-
- % Garching: A town in Germany just north of Munich, where the Max
- Planck Institute for Plasma Physics (see entry) is located. "Garching"
- in plasma physics frequently refers to the Max Planck Institute.
-
- * Gas Blanket: A cold, dense volume of gas surrounding a hot
- plasma and used to protect a material wall from bombardment
- by hot ions (with subsequent sputtering and impurity production).
-
- ! Gauss, Carl Friedrich: (1777-1855) German mathmetician, astronomer
- and physicist.
-
- $ Gauss - unit of magnetic field strength (CGS units)
- 10,000 gauss = 1 tesla (see also Tesla)
-
- & Gaussian Units - See CGS Units
-
- % General Atomic: U.S. corporation involved in fusion research;
- operates the DIII-D device in San Diego; see also Doublet III-D.
- (Officially known as GA Technologies, I believe; or is that the
- name of the parent company???)
-
- & Getters: Materials which absorb ("get") atoms and can be
- used in purifying near-vacuum atmospheres.
-
- $ Gigawatt: Unit of power equal to 10^9 watts, 1000 megawatts,
- or 1 million kilowatts. See entry for watt. 1 gigawatt is a typical
- size for a nuclear fission reactor, and is expected to be the typical
- size of a fusion reactor.
-
- * Glow Discharge: Low-density, low-temperature plasma discharge
- (such as in a fluorescent light) which, well, glows. Sputtering
- in glow discharges is useful in plasma processing of materials.
- The voltage applied to the plasma must be greater than the
- ionization potential of the gas used; most of the plasma voltage
- drop is near the cathode, where the majority of ionization occurs.
- Discharge is sustained by secondary electrons emitted when ions
- or recombination radiation impact on the cathode; electrons are
- accelerated away from the cathode and ionize neutral gas in the
- discharge.
-
- * Glow Discharge Cleaning: Cleaning in which impurities are
- removed by sputtering in a glow discharge. (?)
-
- * Grad-Shafranov Equation: Reduced MHD-equilibrium equation for
- an axisymmetric, toroidal plasma. (Similar reduced equations
- can be derived for the cases of helical symmetry and for
- the straight cylinder.) Analytic and numerical studies of these
- equations are important in exploring potential plasma
- configurations.
-
- -> Additional info Contributed by James Crotinger, with minor
- revisions:
-
- The lowest order force balance in the plasma is simply that
- the Lorentz force must be balanced by the pressure force.
- This balance, combined with Maxwell's equations, determines
- the equilibrium configuration of the magnetic field. When
- the toroidal configuration is axisymmetric, and the equilibrium
- plasma flow is zero, the magnetic field may be written in
- terms of a stream function \psi that satisfies the
- Grad-Shafranov equation
-
- \Delta*\psi = - \mu_0 R^2 p'(\psi) - FF'(\psi).
- Here p is the plasma pressure and F = R B_\phi.
- (R is the radial distance from the axis of the machine)
-
- (Alternatively, leaving out the equation):
- In an axisymmetric torus, in the absence of equilibrium plasma
- fluid flows, the magnetic field may be written in
- terms of a scalar potential. When the plasma is in equilibrium
- (forces balance and the plasma is stationary), this scalar
- potential obeys a non-linear elliptic equation known as the
- Grad-Shafranov equation.
-
-
- & Gradient: Mathematical term for the operator which determines
- the magnitude and direction of the greatest rate-of-change of a
- given function with position. Similarly used to describe such
- a rate-of-change. For instance, at a given point on a hill, the
- slope of the hill in the steepest uphill direction is the gradient
- of the altitude funtion for the hill.
-
- & Gravitational Force: Force which attracts two bodies together
- based on the product of their masses and the reciprocal of
- the square of their distances. "Gravity" is the force field
- created by one massive body (like the earth) which another body
- (like you) will experience.
-
- * Gross National Product: Total value of goods and services
- produced in a country; measure of economic strength of a nation.
-
- $ Gray: A unit of absorbed dose of radiation, equal to one
- joule of energy per kilogram of mass. 1 Gray = 100 rads.
- Defined relative to the material into which such radiation passed,
- which should therefore be specified.
-
- & Group Velocity: This is derived from the dispersion relation
- (see entry) as Vgroup = dw/dk; the group velocity is the rate
- at which modulations or information within a wave travel through
- a given medium.
-
- * Guiding Center: Particles placed in a magnetic field will
- gyrate in circles around the magnetic field lines, and drift in
- various directions. The guiding center represents the
- instantaneous center of the circular motion. The idea is that
- you can think of the guiding center as drifting, and the particle
- as orbiting the guiding center.
-
- * Gyrofrequency: See cyclotron frequency.
-
- * Gyromagnetic Ratio: Ratio of the magnetic moment to the
- angular momentum of a particle. (see magnetic moment, angular
- momentum)
-
- * Gyroradius: radius of charged particle in magnetic field.
- Same thing as cyclotron radius, Larmor radius.
-
- * Gyrotron: A device for producing microwave energy that
- utilizes a strong axial magnetic field in a cavity resonator
- to produce azimuthal bunching of an electron beam.
-
-
-
-