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Term Definition
saddleblock see “monoblock”
safety actuation system The collection of equipment required to accomplish the necessary safety actions when initiated by the protection system.
safety factor 1) (Elec.) The amount of load, above the normal operating rating, that a device can handle without failure. 2) An overload factor in design to ensure safe operation.
safety systems Systems important to safety, provided to assure the safe shutdown of the plant or to limit the consequences of anticipated operational occurrences or accident conditions.
sawtooth, sawteeth Magnetohydrodynamic instabilities that create oscillations in a plasma, which result in plasma disruptions.
sawtooth stabilization Various methods of stabilizing sawteeth oscillations (which induce disruptions in the plasma) in tokamaks.
scaling laws Laws stating that if two quantities are proportional and are known to be valid at certain orders of magnitude, then they can be used to calculate the value of one of the quantities at another order of magnitude.
scheduled down time The down time of the plant according to plan.
scheduled non-operating state When the plant or component is down according to plan for the length of the scheduled down time.
scrape-off layer SOL, the region of plasma between the last closed flux surface and the surrounding walls.
second stability regime A theoretically predicted regime of a plasma which can sustain very high plasma pressures.
second stable core regime The second stability regime in the central region of a plasma.
separatrix The last closed flux surface.
shear See magnetic shear. Also mechanical shear, due for example to twisting of a body, a stress in the plane parallel to the twisting force.
shut-down time The time span between the end of burn and the end of the plasma state; part of the operating time.
SI (Système International), International Standards
single failure
A random failure which results in the loss of capability of a component to perform its intended safety functions. Consequential failures resulting from a single random occurrence are considered to be part of the single failure.
single-null equilibrium See double-null equilibrium
sintered Agglomeration in metal (or ceramic particles) by heating and compression.
SN single null (divertor)
SOB start of burn
SOF start-of-current flattop
SOFE IEEE Symposium on Fusion Engineering
SOFT Symposium on Fusion Technology
SOL scrape off layer
spectroscopy system A plasma diagnostic system based on observing the light emission from the plasma.
SS stainless steel
stagnation point (Fl. Mech.) A point in a field of flow about a body where the fluid particles have zero velocity with respect to the body.
steady state operation The operation of the plasma in a way in which termination of the pulse is not determined by plasma behaviour, but is rather a choice of the operator. Operation which in principle can continue indefinitely.
steady-state (Phys.) The condition of a body or system in which the conditions at each point do not change with time, that is, after initial transients or fluctuations have disappeared. In dynamic equilibrium, with entropy at its maximum.
superconducting coil Magnetic coils which use superconductors that have zero resistivity when cooled below the critical temperature.
superconducting magnets
Superconducting magnet coils which circumscribe the torus to confine the plasma within and away from its inner surface.
superconductivity The flow of electric current without resistance in certain metals and alloys at temperatures near absolute zero.
superconductor A type of electrical conductor that permits a current to flow with zero resistance.
supercritical Helium will remain liquid in a bath at 1 atmosphere pressure provided the temperature does not rise above 4.2K. If the JT-60SA coils are placed in such a coolant bath and a high pulse of heat ensues in their operation, most of the helium must be vented to avoid large overpressures. To avoid this, the coils operate with pumped supercritical helium, just above the critical temperature, which retains a large measure of the heat transfer properties of liquid helium, without the risk of overpressure.
superinsulation (Chem. Eng.) A multilayer insulation for cryogenic systems, composed of many floating radiation shields in an evacuated double-wall annulus, closely spaced but thermally separated by a poor-conducting fibre.
support systems Systems which provide services to a main plant system or systems. The term is relative. Thus tokamak support systems include heating and cooling, whereas support systems for the heating system include their electrical and cooling systems.
surface contamination Contamination that is the result of the deposition and attachment of foreign materials to a surface.
synchrotron radiation Radiation emitted by very fast, charged particles in a magnetic field as a result of their natural gyration in that field. Particle gyrations are at the cyclotron frequency.
system availability
A figure-of-merit useful in quantifying system effectiveness, normally facility up-time divided by planned up-time.

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  Updated 13 February, 2017