Fusion glossary
S
The scrape-off layer (or SOL) is the plasma periphery—the critical buffer region between the hot core and the solid wall elements.
Defines the plasma edge and acts as a boundary between open and closed magnetic field lines.
The technique selected for disruption mitigation on ITER. A shattered pellet injector pre-empts plasma disruptions by releasing a spray of frozen deuterium-neon pellets into the plasma. The frozen pellet fragments, injected at speeds up to 250 metres per second, rapidly decrease the plasma temperature, thereby dissipating energy and minimizing potential damage to plasma-facing surfaces during a disruption.
In ITER, the blanket is subdivided in modules to allow it to be relatively easily replaced through equatorial access ports. There are 440 individual segments, each measuring 1 x 1.5 metres and weighing approximately 4.5 tonnes. Each segment has a detachable first wall which directly faces the plasma and removes the plasma heat load, and a semi-permanent blanket shield dedicated to neutron shielding. (see also "First Wall").
The time span between the end of burn and the end of the plasma state; part of the operating time.
The Indian Steady State Superconducting Tokamak (SST-1) was fully commissioned in 2013 at the Institute for Plasma Research in Gujarat, and upgraded in 2019. SST-1 is a medium-sized tokamak producing repeatable plasma discharges up to ~ 500 ms with plasma currents in excess of 75000 A at a central field of 1.5 T. See this website.
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 that, in principle, can continue indefinitely.
A tokamak in which conditions such as temperature, reaction rate, and neutron flux do not change appreciably with time.
A device invented by Lyman Spitzer (USA) for the containment of a plasma inside a racetrack-shaped tube. The toroidal device produces a poloidal field in a plasma with the use of external magnetic field coils.
Magnetic coils which use superconductors that have zero resistivity when cooled below the critical temperature.
The flow of electric current without resistance in certain metals and alloys at temperatures near absolute zero.
A type of electrical conductor that permits a current to flow with zero resistance.
Helium will remain liquid in a bath at 1 atmosphere pressure provided the temperature does not rise above 4.2 K. If the ITER 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 of ITER 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.