Spectroscopic temperature measurements in high temperature gases and plasmas

Various methods of determining temperature distributions in hot gases and plasmas by spectroscopic techniques are reviewed. A large range of temperature from approximately 10 3 to 20*10 3 K is considered. Particular attention is paid to the meaning of temperature at these high temperatures, and in this context the concept of 'local thermodynamic equilibrium' is introduced and approximate conditions for its validity are discussed. A brief account is given of recent work on the use of a wall-stabilized arc as a standard of very high temperature and standard of radiation in the vacuum ultraviolet.