Relativistic Effect in the Light-Scattering Spectrum of a<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>θ</mml:mi></mml:math>-Pinch Plasma

Precise measurements of incoherently scattered light from a $\ensuremath{\theta}$-pinch plasma revealed a blue shift of the spectrum which could not be accounted for either by the diamagnetic drift velocity of the electrons or by the motion of the plasma as observed stereoscopically by a streak camera. We find that a major part of the blue shift can be attributed to a relativistic effect. We discuss the consequences of ignoring the relativistic corrections and point out the possibility of making large systematic errors in electron-temperature measurement in certain experimental arrangements employing Thomson scattering. Even at temperatures well below 1000 eV the effect is not negligible.