P
 
 
 
Term Definition
pancake winding A method of winding a conductor for a magnet (c.f. layer winding). A conductor is wound in a circumferential direction rather than along the axis of a magnet, and forms a unit module like a pancake. 'Pancakes' are wound separately, stacked together, and then jointed electrically (pancake-to-pancake joint) in a series.
particle exhaust Various methods of exhausting particles from a plasma, such as with a divertor or pumped limiter.
passive component A component which does not need any external input to operate.
PBS plant breakdown structure
pedestal physics The transport barrier that occurs just inside the magnetic separatrix in H-mode provides a thin layer where the pressure increases sharply. At the top of this profile “pedestal” density and temperature values serve as boundary conditions for the core profiles. This may be very important if the core temperature gradient turns out to be constrained. The energy content of the pedestal is generally about one third of the total core energy content, and scales differently from the core global scaling. Pedestal physics is a study of this region.
pellet injector A device that shoots small frozen quantities of hydrogen isotopes at high speed into the inner regions of a hot plasma. This method has some penetration advantages over conventional gas injection.
PF poloidal field
PFC plasma-facing component
physical separation
Separation by geometry (distance, orientation, etc.), by appropriate barriers, or a combination thereof.
PID plant intergration document
PL Project Leader
plant subsytem Each component forms part of some functional subsystem of the “plant”. There are about 20 major subsystems, covering every part of the tokamak, the buildings, and all peripheral plant out to the point of interaction with the environment around the plant.
plasma The fourth state of matter. A collection of electrically charged electrons and ions that is approximately "charge neutral" macroscopically.
plasma confinement phenomena Phenomena which affect plasma core energy confinement. The energy confinement time in plasma has been characterised empirically by various machine parameters (e.g. size and current). Explaining why confinement scales in this way requires an understanding of how the different physical processes affecting confinement might interact. This involves a study and modelling of the possible phenomena, and then comparison with experimental results.
plasma current The electrical current going the long way around the torus.
plasma disruption A rapid deposition of plasma energy resulting from the loss of plasma confinement to part of the plasma-facing structure as a result of instabilities.
plasma elongation The ratio of the height of the plasma cross section to its width.
plasma facing components Tokamak components which directly interact with the plasma, and are subject to high heat fluxes. Typical plasma facing components include the first wall, limiter and divertor.
plasma processes Plasma confinement, heating, and energy and particle loss, in the central plasma core, across transport barriers, and in the plasma edge region.
plasma profiles The variation in amplitude of plasma parameters (most often density and temperature of the electrons or ions) across the minor radius of the plasma.
plasma purity The degree to which the plasma is contaminated by items other than the fuel species (deuterium and tritium). The plasma may be contaminated by impurities coming fromthe wall, deliberately or accidentally fed into the bulk plasma, or as a result of the fusion reactions themselves (e.g.helium). Measured by the parameter Zeff.
plasma shutdown The orderly process of extinguishing the plasma at the end of a plasma burn pulse, involving reduction of the plasma thermal energy, and reduction of plasma current to zero.
plasma temperature Temperature expressed in degrees K (thermodynamic temperature) or electron volts (kinetic temperature). A measure of the random kinetic energy (energy of motion) of the ions or electrons present.
plasma volume The volume encompassed by a given plasma in a tokamak or stellarator.
PM Project Manager
PMI plasma-material interaction
PMY professional-man-year, see “PPY”
P-NBI positive ion neutral beam injector
poloidal direction Movement in the vertical plane intersecting the plasma torus along projections in that plane of any of the tokamak’s nested toroidal flux surfaces.
poloidal field PF, the magnetic field generated by an electric current flowing in a ring.
poloidal field coils Components of a tokamak that assist in stabilizing the plasma.
port axis direction The radial symmetry axis of the port extension.
port plugs The vacuum vessel contains a large number of ports. During operation these are filled with specialised equipment for plasma diagnostics, heating, vacuum pumping, limiters, etc.. Each item of this equipment is housed in a specialised port plug which provides a consistent interface with the adjacent vessel and blanket, adequate shielding, and links for port plug services to external supplies.
POS plasma operation state
position/reaction force detection sensors A system of mechanical or piezoelectric driven strain gauges.
postulated initiating events Identified events that lead to anticipated operational occurrences or accident conditions and their consequential effects.
power tubes Radio-frequency heating systems produce electromagnetic waves of the required power and frequency using high power valves (“tubes”). e.g., the gyrotron, used for ECRH. This consists of an electron gun, an acceleration chamber, a resonance chamber immersed in a strong magnetic field produced by superconducting magnets, and finally a collector to accommodate any energy not transmitted. An electron beam is accelerated into the strong magnetic field. The electrons gyrate at high speed round the field lines and emit an electromagnetic wave with the gyro-frequency. The wave is strongly amplified in the resonance chamber and then transmittted out of the cavity to the target.
PPM professional-person-month
PPY professional-person-year
prescribed limits Limits established or accepted by the Regulatory Body.
primary coolant The fluid circulated through the tokamak to remove heat.
PS power supply
pulse length The interval of time when fusion reactions are taking place in the plasma.

To add a definition, correct an existing one or to request a definition.

 
   
   
   
  Updated 13 February, 2017