Line shapes and plasma movements in hot fusion plasmas

Abstract

ABSTRACT Line shapes in hot fusion plasmas can reflect the existence of velocity shear in the plasma. High resolution spectroscopy is needed to differentiate between line broadening by this effect and thermal line broadening. Weused this technique to study plasma rotation on the RTP tokamak and the T2R reversed field pinch. Line shiftsof hydrogen revealed atom speeds of 40 km/s resp. 20 km/s. Observations of the C IV resonance lines on RTPshowed a relation between changes in velocity shear and the deposition of electron cyclotron heating with respectto the location of electron thermal transport barriers as well as a poloidal rotation of several km/s.Keywords: spectroscopy, fusion plasmas, line shapes 1. INTRODUCTION Line broadening or splitting of spectral lines emitted by hot fusion plasmas can be caused by several reasons.1Natural line broadening can in practice always be neglected. Zeeman splitting or broadening is always present,because the devices used to contain these hot plasmas, like tokamaks, use magnetic fields up to several Teslato contain the plasma. Stark broadening is due to electrical fields in the plasma. Doppler broadening is causedby the high temperatures of these plasmas. If the resolution of the specrometer is high enough and the fieldsin the observation volume are sufficiently homogeneous one sees the splitting in components which otherwisemanifests itself only by line broadening. An important but often overlooked source of line broadening is velocityshear, i.e. different groups of ions move with different speeds and/or in different directions with respect of theline of sight of the observations. Each of these groups emits light with a different shift in wavelength due to theDopplereffect, while each component is broadened due to the temperature (see Fig. 2).