Term Definition
R major plasma radius
R&D research and development
radiated power Power radiated from the plasma by various mechanisms - line radiation (due to emission of quanta as energetic electrons decay to lower states in partly ionised atoms near the plasma edge), bremmstrahlung (“braking radiation” due to acceleration/decelleration of ionised particles as they come near to collision) and synchrotron radiation (due to particles orbiting the magnetic field lines).
ramp-down time The time necessary to terminate the plasma and quench the burn, involving a phase of decrease (ramp-down) of plasma temperature, followed by a decrease (ramp-down) of plasma current.
ramp-up rates Rate of change of plasma current or temperature during their respective ramp-up times.
ramp-up time The time necessary to initiate the plasma and heat it up to burn temperature, involving a phase of increase (ramp-up) of plasma current, followed by an increase (ramp-up) of plasma temperature.
rampdown rates Rate of change of plasma current or temperature during their respective ramp-down times.
realtime observations Continuous display of the value of a plasma parameter at the current moment. In contrast to observations of plasma behaviour and parameters which are determined some time after their actual occurrrence, e.g by post-processing of diagnostic data gathered during a plasma pulse.
relative resistance ratio (Elec.) RRR, the ratio of the resistance of a piece of a material to the resistance of a piece of specified material, such as annealed copper, having the same dimensions and temperature.
remote handling Handling of tools or components by machines with the controls at a remote location.
remote maintenance Maintenance and modification of the radioactive elements and components of the tokamak using machines and tools controlled remotely to avoid human exposure to radioactivity.
residual heat Heat which is produced after the reactions have been terminated.
See also "decay heat".
resistive wall mode The type of discharges proposed for steady state operation are not stable without a perfectly conducting wall at the plasme edge. In ITER and JT-60SA, with the resistive wall some distance from the edge, the result is that RWMs, a type of MHD instability, occur and grow on the timescale of the magnetic field penetration through the wall. The external control coils are therefore used to control these modes.
retrofit To furnish or provide with new equipment or parts unavailable at the time of original manufacture or construction.
reversed shear A variation in magnetic shear which changes sign as one moves across the plasma.
RF radio frequency
RH remote handling
RO (Technical) Responsible Officer
“rolled up” (Idiom.) The act of summing detailed data into more general summary data.
RRR relative resistance ratio
runaway electrons Those electrons in a plasma that gain energy from an applied electrical field at a faster rate than they lose it through collision with other particles. These electrons tend to "run away" in energy from the remainder of the plasma.

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  Updated 13 February, 2017