AN INVESTIGATION OF THE ACCURACY OF DOPPLER BROADENED LINE PROFILE ANALYSIS APPLIED TO PLASMA DIAGNOSTICS

Abstract A method for spectral line width measurements has been developed in order to compute the impurity ion temperature from Doppler broadening in the EXTRAP-T1 Reversed Field Pinch experiment. The equipment used is a 1-m Czerny-Turner spectrometer and a gated, intensified 1024 pixel Optical Multichannel Analyser. This paper describes the numerical methods used to extract the ion temperature from Doppler broadened line profiles. Extensive simulations have been made in order to estimate the error introduced in the Doppler broadening (ion temperature) and Doppler shift due to the lineshape fitting process and photon statistics. The noise characteristics of the Optical Multichannel Analyser has been shown to deviate from any simple distribution function, e.g. Poisson statistics, over a line profile. It instead shows an intensity dependent distribution. A lowest measurable limit of line broadenings has also been estimated.