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Subject: Conventional Fusion FAQ Glossary Part 16/26 (P)

This article was archived around: 11 Nov 1999 12:26:02 GMT

All FAQs in Directory: fusion-faq/glossary
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Archive-name: fusion-faq/glossary/p 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 16: Terms beginning with "P" 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). ================================================================== PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP # p, P: Variables used for plasma (kinetic) pressure. # p: also used as symbol for the proton $ p: also the metric prefix for pico (10^-12 * base unit) @ PBFA-II: Particle Beam Fusion Accelerator-II; see entry @ PBX-M: Princeton Beta eXperiment-Modified; see entry @ PCS: Plasma Control System (Alcator C-Mod) @ PCX: Neutral Particle Analyzer @ PDX: Poloidal Divertor eXperiment; see entry @ PEOS: Plasma Erosion Opening Switch; see entry for Plasma Opening Switch (POS) @ PEP: Pellet Enhanced Performance; see entry on pellet injection @ PEST: Plasma Equilibrium and STability code; see entry @ PF: Poloidal Field; Poloidal Field Magnet Coil @ PLT: Princeton Large Torus; see entry @ PNL: Pacific National (Northwest?) Laboratory; no entry yet. @ POS: Plasma Opening Switch; see entry @ PPPL: Princeton Plasma Physics Lab; see entry @ PV: Photo-Voltaic; see entry @ PWR: Pressurized Water Reactor (fission); see entry * Parametric Instability: Instability which occurs in a system whose equilibrium is weakly modulated in time or space. The modulation produces a coupling of the linear eigenmodes of the system and can lead to destabilization. & Particle: > Particle Beam Fusion Accelerator II: Light ion accelerator inertial confinement fusion research system at Sandia National Laboratories. & Particle Density: number of particles present per unit volume (typically a cubic centimeter). See also density; typically represented by the variable "n". * Pellet Injection / Pellet Injector: This is a device which accelerates (shoots) small (less than 4 mm diameter) frozen pellets of hydrogen (or other) isotopes; these are then launched at high speed (ca. 1000 m/sec) into the inner regions of hot plasmas. Use of lithium and boron pellets allows coating of the vacuum vessel walls, and is useful for impurity control. Pellet injection can also be used to fuel the plasma, and the light emitted by the pellet's ablation cloud is useful for diagnostic purposes. * Pfirsch-Schluter Regime, P-S Transport: One of the neoclassical transport parameter regimes in a tokamak plasma; characterized by the collisional mean free path being shorter than the connection length. (This is the high-collisionality end of the spectrum; plateau transport is in the middle, and the banana regime is on the low-collisionality end.) In this regime the diffusion coefficient is q^2 times greater than the classical value (q being the safety factor, q > 1). See also classical transport, neoclassical transport, plateau transport, banana transport, safety factor. & Phase Velocity: Defined as w/k, this describes the rate of propagation of a wave through space. & Photoionization: The ionization of an atom or molecule by the collision of a high-energy photon (i.e., electromagnetic radiation) with the particle. & Photo-voltaic: Adjective used to describe devices which convert light, particularly solar energy, into electricity. $ pico-: Metric prefix indicating 10^-12 times the base unit. * Pinch effect: General term for a class of phenomena whereby the plasma is compressed or restricted ("pinched"). There are a variety of types of pinches. The Z-pinch is a constriction of a plasma carrying a large current, caused by the interaction of that current with its own encircling magnetic field. The Theta pinch is a constriction of a plasma by an increase in the axial magnetic field generated by an external solenoidal current. The Ware pinch arises in tokamaks due to neoclassical effects. And there are others. > Pinch Device or Pinch Machine: Device which confines plasma using a pinch effect. (Typically the Z or Theta pinch.) * Pinch Reflex Diode: A self-insulated ion diode in which the magnetic field from the ion and electron flow alone provide electron control, and the ion source is an anode plasma formed by relexing the electrons through a thin plastic foil. * Pitch Angle: For a charged particle moving in a magnetic field, this is the angle arctan (v-perp/v-parallel), where v-parallel is the component of the particle's velocity parallel to the magnetic field, and v-perp is the perpendicular component. The pitch angle is zero when the particle moves purely parallel to the field, and 90-degrees when the particle has no parallel velocity at all. * Pitch Angle Scattering: Scattering (collisional, or due to wave-particle effects) of particles in velocity space, in which the pitch angle (see entry above) is changed. * Plant Factor: Another term for Capacity Factor; see entry. * Plasma: A "Fourth State of Matter" in which many of the atoms or molecules are ionized. Plasmas have unique physics compared to solids, liquids, and gases. (Most plasmas can be thought of at first as extremely hot gases, but their properties are generally quite different.) Some (but not all!) Examples: the sun, fluorescent light bulbs and other gas-discharge tubes, very hot flames, much of interplanetary, interstellar, and intergalactice space, the earth's ionosphere, parts of the atmosphere around lightning discharges, and of course fusion plasmas. * Plasma Beta: see Beta * Plasma, Cold: See Cold Plasma Model * Plasma Containment: (quoting from the PPPL Glossary of Fusion Terms) "In plasma physics experiments or nuclear fusion experiments, operation is intended to prevent, in an effective and sufficiently prolonged manner, the particles of a plasma from striking the walls of the container in which this plasma is produced. Plasma confinement is a fundamental requirement for obtaining net energy from a fusion plasma. The reason is that scattering (hence diffusion) is at least an order of magnitude more probable than fusion reactions. Hence, without confinement, the plasma fuel would disperse before enough fusion reactions could take place." * Plasma Equilibrium and STability Code: (PEST) This is a widely-used, well-developed computer simulation ("code") used to calculate MHD equilibrium and stability in various fusion devices. > Plasma Focus: The Plasma Focus is another device which depends on the pinch effect. Possible applications include both fusion and plasma propulsion, as well as other plasma research. In essence the plasma focus is generated by discharge of a current across the ends of two coaxial insulated conducting pipes. The Plasma Focus caused a huge stir when they generated copious neutrons, until it was discovered that the source of the neutrons was knockoffs from deuterium due to pinch accelerated electrons or ions. Plasma focus is sort of a point version of the "Z"pinch. For more information on the plasma focus, see the entry in the section on confinement approaches (4B). * Plasma Frequency: The natural collective oscillation frequency of a charge species (electrons, ions, etc.) in a plasma, in the absence of (or at least parallel to) a magnetic field. Also known as Langmuir or Langmuir-Tonks frequency; see also electrostatic waves, plasma oscillations. * Plasma Oscillations: Class of electrostatic oscillations which occur at/near the plasma frequency (see entry) and involve oscillations in the plasma charge density. Also known as Langmuir Oscillations; In Stix's _Waves in Plasmas_ these are called Langmuir-Tonks Plasma Oscillations. * Plasma-Plasma Reaction: Fusion reaction which occurs from the collision of two thermal plasma ions. (See also beam-wall, beam-beam, and beam-plasma reaction entries.) * Plasma Wave: A disturbance of a plasma away from equilibrium, involving oscillations of the plasma's constituent particles and of an electromagnetic field. Plasma waves can propagate from one point in the plasma to another without net motion of the plasma. > Plasmak: Controversial advanced spheromak-type concept using a fluid rather than solid conducting shell and a plasma with purely internal magnetic fields, whose pressure is supported by a surrounding gas; for more information see entry in section 4. * Plasmoid: An isolated plasma which holds together for a duration much longer than the collison times for the consituent particles. * Plateau Region, Plateau Transport: The collision frequency (and transport) regime characterized by an effective coulomb scattering rate equal to or greater than the poloidal transit ("bounce") frequency, but where collisional mean free path is less than the connection length (2qR*PI). In this regime, the transport coefficients are independent of the collision frequency. (Thus a plot of transport coefficients vs. frequency becomes horizontal line in this regime, forming a "plateau" in the graph; hence the name.) & Plutonium: Radioactive metallic element (Pu). The primary isotope, plutonium-239, is a product of neutron absorption by U-238, esp. in fission reactors. Pu is used in nuclear weapons and as a fission reactor fuel. * Poisoning: Buildup of ash and impurities in a fusion plasma tends to reduce the quality of the plasma and reduce the fusion output; this sort of process is sometimes called "poisioning" the reactor or the plasma. See also ash, impurities. & Polarization: * Polarization of Reacting Particles: See Spin-Polarized Fusion. * Poloidal: In toroidal geometries, the direction along the circumference of a slice through one side of the torus. "The short way around a torus". - Albert Chou, albert@seas.ucla.edu * Poloidal Divertor: A divertor (see entry) which takes a bundle of poloidal field lines, forming a separatrix in the poloidal magnetic field which creates separate plasma regions (which can then have different physical parameters, since transport is reduced across the separatrix where q => infinity). > Poloidal Divertor Experiment: (PDX) A medium-size, high-current divertor tokamak which was operated at Princeton, whose primary research objective was to determine the effectiveness of poloidal magnetic divertors in controlling impurities in reactorlike fusion plasmas. PDX was modified and became PBX, which was modified again and is now PBX-M (see entry for Princeton Beta Experiment). * Poloidal Field: In toroidal devices, the magnetic field that encircles the plasma axis. (i.e., loops around the torus "the short way".) * Poloidal Field Coils: In toroidal devices (eg, tokamaks), the sets of windings which are (typically) aligned along the plasma axis and produce poloidal fields. These include ohmic heating, shaping, vertical, equilibrium, and divertor windings. * Poloidal Field Windings: See Poloidal Field Coils above. * Positive Column: The luminous glow, often striated, which occurs between the Faraday dark space and the anode in a glow discharge plasma tube. & Positron: Antiparticle to the electron; this particle has the mass of the electron but the opposite charge. * Positron Emission: Form of nuclear decay where a proton disintegrates into a neutron, positron, and some sort of neutrino. (?) & Power: Defined as amount of work per unit time, or change in energy per unit time. * Power Density: In fusion, the rate at which energy is generated per unit volume in the reactor core. (See also entries for power, density.) & Pressure: Defined as force per unit area. * Pressure Tensor: A generalized pressure (can be anisotropic) which plays a role in MHD (see entry) analogous to that of pressure in ordinary fluid mechanics. > Pressurized-Water Reactor (fission): Type of nuclear reactor where the coolant is water kept under pressure to prevent it from turning to steam inside the plant. (I think!) * Price-Anderson Act: U.S. Federal law passed in the 1950s (?) which limits utility liability for nuclear fission plant accident damages. U.S. Government effectively insures the utilities against external costs associated with nuclear accidents. * Primary Energy: Energy before conversion. For instance, the United States uses about 30,000 megajoules of electricity per capita per year, but electricity is generally obtained by converting other forms of energy (primarily chemical/heat) at an efficiency of around 30%, so the U.S. consumes 90,000 megajoules of primary energy per capita for electrical use. (Total U.S. primary energy consumption is 300,000 megajoules per capita.) % Princeton - See Princeton University and/or Princeton Plasma Physics Lab > Princeton Beta Experiment-Modified (PBX-M): mid-sized tokamak research device at Princeton, which evolved from the Poloidal Divertor Experiment (PDX) machine. Research on PBX is aimed at investigating advanced tokamak regimes, such as indented plasmas (kidney-bean cross sections) with high-beta, providing access to the second-stability regirme. > Princeton Large Torus (PLT): Large tokamak formerly operated at the Princeton Plasma Physics Laboratory (PPPL). Was operated in the 1970s and 80s and studied RF heating and current drive, as well as neutral beam injection heating and other aspects of tokamak physics. Roughly a predecessor to TFTR. % Princeton Plasma Physics Lab (PPPL): Located in Princeton, New Jersey. Single largest fusion research facility in the United States; sole U.S. single-purpose plasma physics laboratory; operated by Princeton University for the Department of Energy. Site of PLT, PBX-M, TFTR, several other past and present experiments, and future site of TPX. (Refer to entries for relevant machines, both here and in FAQ.) % Princeton University: Among other research activities, the University operates the Princeton Plasma Physics Laboratory for the Department of Energy (see above entry for PPPL). * Process Heat: Heat produced by a powerplant (could be a nuclear reactor, or a fusion reactor someday) and used directly for industrial processes, such as metals manufacturing or chemical production. * Project Matterhorn: Code name of the United States' first secret controlled fusion project, started by Lyman Spitzer at Princeton University in 1951. Became a subprogram within Project Sherwood (see entry below.) * Project Sherwood: Name often used to describe the U.S. controlled fusion program in the 1950s and '60s. * Proliferation (nuclear): Proliferation generally describes the way something spreads (rapidly) from one area to another; in the case of nuclear weapons, nuclear proliferation refers to the spread of nuclear bomb-building technology from one state to another. > Proto II: A high-power (10 TW) pulsed (24 ns) electron accelerator which was (is?) used for inertial-confinement research. & Proton: (from Herman) An elementary particle found in the nucleus of all atoms. It carries a single positive electrical charge. & Pulse Height Analyzer: Instrument which records and stores pulses and indicates ("Analyzes") the number of pulse occurrences falling within each of a set of amplitude ("height") ranges. * Pulsed Power: The technology of using electrical energy stores for producing multi-terawatt (10^12 Watts or higher) pulses of electrical power for inertial confinement fusion, nuclear weapon effects simulation, and directed energy weapons. High efficiency and cost effectiveness make it desirable technology for large energy experiments. * Pumpout: Name given to the anomalously high loss of particles to the walls in (some) stellarator discharges; the loss rate when pumpout occurs is substantially greater than that expected from normal classical diffusion processes.