IMPROVEMENT OF ION TEMPERATURE-PROFILE DETERMINATION FROM CHARGE-EXCHANGE MEASUREMENTS BY INCLUSION OF TOTAL-NEUTRAL-FLUX DATA

The reconstruction of ion temperature profiles from energy-resolved ne utral flux measurements in the energy range from 20 eV to 20 keV revea ls an uncertainty in positioning the steep gradient region at the plas ma edge, even if the measured energy range of the neutral fluxes inclu des ion temperature values of the gradient region. This empirical obse rvation is studied analytically with a simple model for the neutral pa rticles. Using the line integral of the electron density one finds tha t translations of the whole ion temperature spectrum with respect to t his coordinate cannot be resolved below a certain value. It turns out that the lowest energy for which fluxes can be measured as well as the accuracy of the Bur measurements determine the amount of uncertainty, which is in our case 1 x 10(17) m(-2). To reduce this uncertainty, th e total neutral flux which is determined mainly by neutrals with energ ies of a few eV or less, has been fitted simultaneously with the absol utely calibrated energy-resolved flux spectra. The total neutral Bur c an be measured with an ion gauge and is closely related to the Il, emi ssivity. The fit of the total neutral flux or the Il, signal requires simulation of the ionization zone in the scrape-off layer, i.e. measur ed electron temperatures must be combined with an accurate model for t he dissociation and ionization of molecules and atoms.