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Conventional Fusion FAQ Glossary Part 16/26 (P)

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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
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Glossary Part 16:  Terms beginning with "P"


Edited by Robert F. Heeter,

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).


# 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 

& 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 

> 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

* 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,

* 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

* 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 

* 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 

& Proton: (from Herman) An elementary particle found in the
nucleus of all atoms.  It carries a single positive electrical

& 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.

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