Numerical simulation of a system for ion temperature measurement by Thomson scattering in a tokamak

• Published in: Journal of applied physics 1981-05, Vol.52 (5), p.3249-3254
• Main Authors: Watterson, R L, Siegrist, M R, Dupertuis, M A, Morgan, P D, Green, M R
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.329195

A numerical simulation of tokamak ion temperature measurement by collective laser Thomson scattering was performed including a Monte-Carlo technique to model the statistical properties of power spectrum estimation. The accuracy to which the ion temperature Ti, may be determined under the influence of a finite laser pulse length, a limited signal-to-noise ratio, unequal electron and ion temperatures, and the presence of heavy impurities was investigated. It is found that the effects of low-frequency plasma turbulence and heavy impurities on the scattered spectrum may be mitigated (and the required heterodyne receiver intermediate frequency bandwidth reduced) by considering only the high-frequency portion of the scattered spectrum. A ratio of total scattered power to total noise power of 1 to 2 is shown to be sufficient to determine Ti. A higher signal-to-noise ratio provides little enhancement in the accuracy of Ti determination. Improved values of Ti may be achieved by a longer laser pulse. A laser pulse at least 1 μsec long is required to measure Ti to within 10% with a signal-to-noise ratio of 2- and 2-GHz heterodyne receiver intermediate frequency bandwidth.