The effect of the instrument function on Doppler ion temperature measurements of the JET plasma
Measurements of the ion temperature of the JET plasma are made from the Doppler broadening of XUV spectral lines recorded with the KT4, Schwob-Fraenkel survey spectrometer. Calculations are used to demonstrate that the shape of the instrument function can have a significant effect on the measurement, in that the neglect of the line wings can lead to the ion temperature being systematically overestimated by up to 30%. A consideration of the random errors suggests that with the often used, 600g/mm grating (slit 20microm), measurements obtained from short wavelength lines (-30Å) are of questionable value, even if higher orders are used. At longer wavelengths (>200Å) the measurements can be useful providing a low temperature limit (~4keV for C lines, ~5kEV for O lines and ~10keV for Ni lines) is set, below which any measurement is disregarded. The general assumption that the precise shape of the instrument function can be neglected when making ion temperature measurements if the broadening is large (~10x) compared with the instrument function, is found to be untenable. A possible explanation of the discrepancy between the charge exchange and X-ray ion temperature measurements is suggested.
Bibliographic Reference: Report: JET-R(88)12 EN (1988)
Availability: Available from the Publications Officer, JET Joint Undertaking, Abingdon, Oxon. OX14 3EA (GB)
Record Number: 198910435 / Last updated on: 1994-12-01
Original language: en
Available languages: en