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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 13/26 (M)
- Supersedes: <fusion-faq/glossary/m_934543711@rtfm.mit.edu>
- Followup-To: sci.physics.fusion
- Date: 11 Nov 1999 12:25:47 GMT
- Organization: Princeton University
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- Expires: 23 Feb 2000 12:24:17 GMT
- Message-ID: <fusion-faq/glossary/m_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: 1995/02/19
- Originator: faqserv@penguin-lust.MIT.EDU
- Xref: senator-bedfellow.mit.edu sci.physics.fusion:44261 sci.answers:10858 news.answers:170844
-
- Archive-name: fusion-faq/glossary/m
- Last-modified: 18-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 13: Terms beginning with "M"
-
- 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).
- ==================================================================
-
- MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMM
-
- # m, M: variable typically used for mass.
-
- $ MA: MegaAmpere or MegAmpere; see Mega, Ampere
-
- $ m: meters; SI unit of distance
-
- $ M: metric prefix "mega", meaning million
-
- @ MARS: Mirror Advanced Reactor Study; see entry
-
- $ MeV: Millions of electron volts; see mega, electron-volt.
-
- @ MFE: Magnetic Fusion Energy
-
- @ MFTF-B: Mirror Fusion Test Facility; see entry
-
- @ MHD: Magnetohydrodynamics; see entry
-
- @ MHD Instability: see Magnetohydrodynamic instability.
-
- @ MHTGR: Modular High-Temperature Gas-Cooled Reactor; see entry.
-
- @ MIT: Massachusetts Institute of Technology; see entry
-
- @ MITL: Magnetically Insulated Transmission Line; see entry
-
- @ MIX 1: see entry under "MIX 1"
-
- @ MKS: Meters, Kilometers, Seconds - see SI Units
-
- @ MKSA: Meters, Kilometers, Seconds, Amperes - See SI Units.
-
- @ MMX: Multiple Mirror eXperiment; see entry
-
- @ MS: Maryland Spheromak; see entry
-
- @ MTX: Microwave Tokamak eXperiment; see entry
-
- $ MW: Megawatt; one million watts; see entry for watts.
-
- * Mach-Zender Interferometer: This is a variation of the Michelson
- interferometer which is used mainly in measuring the spatial variation
- in the refractive index of a gas (or plasma). A Mach-Zender
- interferometer uses two semi-transparent mirrors and two fully
- reflective mirrors located at the corners of a rectangle. The
- incoming beam is split in two at the first semi-transparent mirror,
- and the two halves of the beam travel along separate paths around
- the edge of the rectangle, meeting at the opposite corner. Typically
- one beam is a control, and the other travels through the system
- under study. The two beams meet at the second semi-transparent
- mirror, after which they are mixed together and interfere.
-
- % Madison: See University of Wisconsin-Madison
-
- * Magnetic Axis: This typically refers to the location of the
- innermost flux "surface" in a toroidal device, the one which
- encloses no volume and has therefore degenerated from a flux
- surface into a single field line. Roughly, the circle through
- the middle of the dough of the donut. Additionally, in systems
- with magnetic islands (see entry below), each island has a
- local magnetic axis, distinct from the overall magnetic axis
- of the torus.
-
- * Magnetic Bottle: Colorful term used to describe a magnetic
- field structure which confines a plasma "like in a bottle".
-
- * Magnetic Confinement: Use of magnetic fields to confine a
- plasma. (Confinement involves restricting the volume of
- the plasma and/or restricting particle or energy transport
- from the center of the plasma to the edge.)
-
- * Magnetic Confinement Fusion: Method of fusion which uses
- magnetic fields / magnetic bottles to confine a hot plasma
- until fusion occurs.
-
- * Magnetic Diffusion:
-
- * Magnetic Field:
-
- * Magnetic Field Coil: Coiled current-carrying wires used to
- generate magnetic fields.
-
- * Magnetic Flux Surfaces:
-
- * Magnetic Force Parameter: A dimensionless number equal to
- [(magnetic permeability squared) * (magnetic field strength squared) *
- electrical conductivity * characteristic length of system in question] /
- [(mass density) * (fluid velocity)]. This measures the strength
- of magnetic forces relative to the plasma's inertia.
-
- * Magnetic Island: A magnetic topology near a "rational surface"
- (see entry) where the flux surface is broken up into tubes which
- are not connected with each other poloidally. Islands may develop
- in non-ideal magnetohydrodynamic fluids, where electrical
- resistance becomes important and magnetic field lines are no
- longer "frozen-in" to the fluid. Then magnetic tearing and
- reconnection may allow field lines to link up and form "islands"
- with a local magnetic axis (see entry) in a narrow region near
- a rational surface (see entry). (See also MHD, frozen-in law).
-
- The development of islands may be caused by a small perturbation,
- whether internal or external, whether deliberate or accidental,
- and is usually associated with enhanced transport (i.e., reduced
- confinement). The centers of the islands are magnetic O-points,
- while the boundaries between islands are marked by X-points (see entries).
-
-
- * Magnetic Limiter: See divertor.
-
- * Magnetic Mach Number: A dimensionless number equal to the
- ratio of the velocity of a fluid to the velocity of Alfven
- waves in that fluid. (See also entry for Alfen waves.)
-
- > Magnetic Mirror: See mirror effect, mirror device
-
- * Magnetic Moment: (a) A vector associated with a magnet, current
- loop, or particle; the cross product of this vector with the
- magnetic field is equal to the torque which the field exerts on
- the system. (b) The adiabatic invariant associated with the
- rapid gyromotion of a charged particle in a slowly varying
- magnetic field. (The value of the magnetic moment in sense (b)
- is the magnitude of the vector in sense (a).)
-
- * Magnetic Number: A dimensionless number equal to the square
- root of the magnetic force parameter.
-
- * Magnetic Pressure: Pressure which a magnetic field is capable
- of exerting on a plasma; equal to the magnetic energy density;
- proportional to B^2. (The proportionality constant
- is 1/(2*mu-o) in SI units, 1/8pi in CGS units).
-
- * Magnetic Probe: A conducting coil (sometimes insulated and
- inserted into the plasma) will have an induced voltage due
- to changes in the magnetic flux through the coil, and can therefore
- be used to measure changes in magnetic field strength. Small
- coils used to measure the local field strength are known as
- probes. (Other plasma diagnostics using this effect are the
- Rogowski coil, the voltage loop, and the diamagnetic loop.)
- Magnetic probes placed outside a toroidal plasma which are used
- to measure the poloidal magnetic field are also called Mirnov coils.
-
- * Magnetic Pumping: Form of plasma heating where the plasma is
- successively compressed and expanded by means of a fluctuating
- external magnetic field. (See also adiabatic compression, frozen-in
- law.)
-
- * Magnetic Reconnection: (entry by John Cobb, with some
- modifications) When a plasma has some resistivity, then the
- frozen-in flow requirement is relaxed (see frozen-in flow). In that
- case, the magnetic field can move through the plasma fluid on the
- resistive (magnetic diffusion) time scale. (Typically slow compared
- to MHD timescales.) This allows field lines to reconnect with each
- other to change their topology in response to magnetic and other
- forces in the plasma. (see also Helicity, which is not conserved when
- reconnection is significant.) The predominant theory for solar
- flares is based on the transfer of energy from magnetic fields to
- plasma particles which can occur in reconnection. Reconnection can
- also be studied in the laboratory.
-
- * Magnetic Stress Tensor: A second-rank tensor, proportional
- to the dyadic product of the magnetic field (B) with itself.
- The divergence of the magnetic stress tensor gives that part
- of the force which a magnetic field exerts on a unit volume of
- conducting fluid due to the curvature of the magnetic field lines.
-
- * Magnetic Switching: The use as switches of saturable inductors for
- producing high power pulses without electrical arcs. This is a
- principal technology for extending single-shot accelerators in
- light-ion-beam-driven inertial confinement fusion to repetitively
- pulsed devices for possible reactors. Three terawatt, 200 KJ
- magnetic switches have been developed for fusion drivers at
- Sandia National Laboratories. (Info from the 1985 OSTI Glossary
- of Fusion Energy; may be out of date.)
-
- * Magnetic Viscosity: A magnetic field in a conducting fluid will
- damp fluid motions perpendicular to the field lines, similar to
- ordinary viscosity, even in the absence of sizeable mechanical
- forces or electric fields.
-
- * Magnetic Well: see Minimum-B Configuration.
-
- * Magnetically Insulated Transmission Line (MITL): Used to
- transport power efficiently in vacuum lines at very high
- power densities. Although the cathode is a space-charge
- limited electron emitter, the electron flow is confined
- by self-generated or applied magnetic fields. MITL's are
- used extensively in light-ion-driven inertial confinement fusion.
-
- * Magnetohydrodynamics (MHD): Physical model describing the
- properties of electrically conducting fluids interacting with
- magnetic and electric fields. MHD theory is relevant at
- relatively low frequencies and for distance scales larger than
- the Larmor radius. Also known as hydromagnetics.
-
- * Magnetohydrodynamic Generator: A device that extracts
- kinetic energy from a jet of plasma and generates electricity.
-
- * Magnetohydrodynamic Instability (MHD instability):
- Class of unstable (growing, not damped) waves and other
- modes of oscillation which are described by MHD theory.
-
- * Magnetohydrodynamic Turbulence: Motion of a plasma in which
- velocities and pressures fluctuate irregularly.
-
- * Magnetohydrodynamic Waves: Material waves in an electrically
- conducting fluid in the presence of a magnetic field, which
- are described by magnetohydrodynamics.
-
- * Marx Generator: A pulsed-power device invented by Erwin Marx.
- Capacitors are charged in parallel and then quickly discharged
- in series to produce high voltage, high current (and thus
- high power) pulses. Used in light-ion-driven and some
- laser-driven inertial confinement fusion systems.
-
- > Maryland Spheromak: A University of Maryland spheromak
- facility, used to investigate the production, equilibrium,
- stability, and confinement properties of spheromaks.
- (What happened to it?)
-
- * Mass Defect: The energy from fusion reactions comes from the
- difference in mass between the reactants and the products. In an
- energy-releasing reaction, some mass is converted to energy via
- Einsteins famous equation E (energy) = m (mass) * c^2 (speed of
- light squared). The energy released is the difference between
- the binding energies of the reactants and the products (see
- entry on binding energy).
-
- % Massachusetts Institute of Technology (MIT): Located in Cambridge,
- MA (just outside Boston). Home of the Plasma Fusion Center and the
- Alcator series of compact tokmaks.
-
- % Max Planck Institute for Plasma Physics (IPP): In Garching (near
- Munich). The largest plasma physics institute in Germany. Presently
- home of ASDEX-Upgrade and Wendelstein-7AS. (See entries)
-
- ! Maxwell, James Clerk: 19th-century British physicist, responsible
- for the synthesis of the equations of electromagnetism and the
- prediction of electromagnetic waves, among other things.
-
- & Maxwell-Boltzmann Distribution: Distribution function of particle
- velocities (or energies) corresponding to a system in thermal
- equilibrium with a temperature value of T. See also: distribution
- functions, temperature.
-
- & Maxwellian Distribution: see Maxwell-Boltzmann Distribution
-
- & Maxwell ('s) Equations: The key equations governing
- electrical and magnetic phenomena. These are a set of four
- vector partial differential equations relating electric and
- magnetic fields to each other and to electric charges and
- currents.
-
- & Mean Free Path (for a given event, e.g., collisons): Average
- distance a particle travels between occurrences of the given
- event; e.g., between collisions. For collisions, the mean free
- path is roughly equal to unity divided by the product of the
- collision cross section times the particle density.
-
- & Mega-: Metric prefix indicating 1,000,000 times a given quantity.
- e.g., a megawatt is 1,000,000 watts.
-
- * Meltdown: In a fission reactor, if there is insufficient coolant
- or the fission chain reaction proceeds too rapidly, heat can
- build up in the reactor fuel, causing it to melt. In extreme
- cases the whole fission core can melt down to (or even through) the
- reactor floor. Fusion reactors are not vulnerable to this.
-
- & Metastable state: several types
- Electronic
- Nuclear
-
- & Micro-: Metric prefix indicating 1/1,000,000th of a given
- quantity. e.g., a microampere is 1/1,000,000th of an ampere.
-
- * Microinstability: Instabilities due to particle / kinetic-
- theoretical effects, typically occuring on small scales, as opposed
- to those derivable from fluid models valid on larger scales.
- As with other instabilities, these are driven by various types
- of available free energy. (See also kinetic theory.)
-
- * Microwave Interferometer: See interferometer, interferometry.
- A microwave interferometer uses radio waves in the microwave
- frequency (or wavelength) range as the electromagnetic signal.
- Microwave interferometers are used to measure the line-averaged
- density of a plasma along the path through which the microwave
- beam is passed, through phase shifts in the propagated beam.
-
- * Microwave Tokamak eXperiment (MTX): a reincarnation of Alcator C
- at LLNL, now shut down.
-
- > Migma devices: Non-thermal, non-pulsed devices in which fusion
- occurs among the ions of a self-colliding particle beam.
-
- $ mill: financial unit equal to 0.1 cents or 0.001 dollars;
- standard unit which electrical utilities use in charging for
- electricity (e.g., 50 mills/kwh = $0.05/kwh).
-
- > Minimum-B Configuration: Confinement configuration where the
- magnetic field strength is a minimum where the plasma is to be
- confined, and increases in all directions away from the confinement
- region. Stability is favorable in such a configuration because the
- magnetic pressure increases in all directions away from the plasma.
-
- * Mirnov Oscillations: Fluctuations in the poloidal magnetic
- field (of a toroidal magnetic confinement system) which rotate
- in the electron diamagnetic drift direction at a speed comparable
- to the electron diagmagnetic drift velocity and with frequencies
- due to 5-20 kHz. Mirnov oscillations arise from tearing modes.
- Poloidal magnetic probes used to measure the poloidal field in order
- to diagnose Mirnov oscillations (and other MHD phenomena) are
- often called Mirnov coils or Mirnov loops. See relevant entries...
-
- > Mirror Advanced Reactor Study (MARS): This was a collaborative
- effort between government, academia, and industry to design a
- commercial-scale tandem mirror fusion power plant. Participants
- included the Department of Energy (LLNL); University of Wisconsin;
- TRW, Inc.; General Dynamics; EBASCO Services; Science Applications,
- Inc.; and Grumman Aerospace Corp. System was never actually built.
-
- > Mirror device, mirror machine: Generally, linear fusion machines
- which confine the plasma using the mirror effect. Basically there
- is a weak field in the center, and strong fields at the ends.
- Particles are then reflected at the ends by the strong fields,
- and are confined in the center of the device. (Some particles
- will have enough velocity along the axis of the device to escape
- from the mirror, however.)
-
- * Mirror effect: A charged particle travelling into an increasing
- magnetic field will (if the field becomes strong enough) reverse
- direction and be reflected back. This is a direct result of
- the adiabatic invariance (see entry) of the magnetic moment
- (see entry). Plasmas can be confined by devices which utilize
- this effect; see entry above for mirror device. The effect
- also occurs in some toroidal plasmas, since the toroidal magnetic
- field is stronger on the inboard side than on the outboard side;
- in this case it gives rise to so-called "neoclassical" effects.
- The strength of the mirror is determined by the mirror ratio.
- (See relevant entries. Consult an introductory plasma physics
- text for a more technical explanation.)
-
- > Mirror Fusion Test Facility (MFTF): A large mirror device built
- at LLNL from the late 1970s to the mid-1980s, but mothballed
- for political reasons (decrease in magnetic fusion funding)
- just before it was to begin operation.
-
- * Mirror Ratio: In a magnetic mirror, the mirror ratio is the ratio
- between the strongest value of the magnetic field on the mirror's
- axis, and the value at some other point on the axis. In
- a mirror confinement device, the "other point" is taken to be
- the location of weakest field strength between two confining
- mirrors. The mirror ratio is a key factor in determining
- confinement properties of the system.
-
- > MIX-1: A small, gun-injected mirror machine at the University
- of Maryland; was used to study the drift-cyclotron loss cone
- instability (see entries for DCLC, DCLC instability).
-
- * Mobility: The ease with which a charge in a medium (e.g. a plasma)
- moves in response to an electric field. Related to diffusivity and to
- resistivity. Measured by the average equilibrium drift velocity
- attained by the charged particle when subjected to acceleration
- by a unit electric field and the opposing frictional force of
- collisions with other particles.
-
- * Mode Rational Surface: A magnetic surface on which field
- lines resonate with the helicity of a particular perturbation
- or instability; see also rational surface.
-
- * Moderator: Substance used in a fission reactor to slow down
- ("moderate") energetic fission neutrons so that they are more
- easily captured within the reactor and therefore maintain the
- fission chain-reaction.
-
- > Modular High-Temperature Gas-Cooled Reactor: Class of fission
- reactors under study in the U.S.; designed to run at higher
- temperatures and use gas cooling to achieve greater efficiency
- of conversion from thermal to electric energy.
-
- & Mole: The amount of given substance such that the mass in grams
- is equal to its [atomic weight, molecular weight, mass number].
- The number of particles in a mole of a substance is Avogadro's
- Number N = 6.02497 x 10^23 (see entry). For instance, one mole
- of water weighs 18 grams, since water is H2O, the H's weigh
- one apiece, and the O weighs 16. Heavy water, or D2O, weighs
- 20 grams/mole, because each D weighs 2 instead of 1.
-
- * Molecular ion injection: Heating concept for magnetic
- confinement fusion in which energetic (accelerated) molecular
- ions are injected into the plasma, dissociate, and heat the
- plasma while building up the population of trapped high-energy
- ions. Not widely used (see neutral beam injection).
-
- & Momentum: Basic physical quantity measuring motion; generally
- defined as momentum = mass * velocity. The total momentum of
- all bodies in a system is conserved in all physical processes
- known so far, I believe. Momentum is related to force in that
- force = rate of change of momentum with time. See also force.
-
- * Motor-Generator: Device used to store energy by accelerating
- a rotating flywheel to high speeds; energy may be rapidly discharged
- and converted to shorter-pulse energy. (Used to power TFTR; the
- electric utility would be a little unhappy if TFTR were to suddenly
- draw its 30 MW+ of power at random intervals. :)
-
- > Multiple Mirror eXperiment (MMX): A 10-meter long simple
- mirror facility which was located at the University of California,
- Berkeley.
-
- > Muon-Catalyzed Fusion: Alternative approach to fusion where
- muons are introduced to D-T fluid. The muon is heavy enough that
- it binds more strongly to the D or T than an electron would, and
- the result is that the D and T nuclei in the molecule are drawn
- more tightly together, and fusion results. More detailed discussion
- is given in section 4B.
-
-
-