Using beryllium and polypropylene-aluminium absorbers to measure the TBR-1 tokamak electron temperature

Abstract

Beryllium foils of di erent thickness have been employed for measuring the electron temperature in tokamaks using the absorbing method based on ratio of the bremsstrahlung intensities, emited by the plasma. However, in the case of small tokamaks with low electron temperatures, such as TBR-1, the foils must be very thin, becoming very fragile, hard to handle and with insu cient absorbing power of line radiation from impurities. Also they are very expensive. In this work, we h a ve i n vestigated whether other absorber materials, obtained by depositing Aluminium on polypropylene lms, for example, could give similar results. These new kind of lters have good mechanical properties and are light tight, as opposed to the thin beryllium foils which h a ve shown, very often, the presence of pinholes. Also, the attenuation of the line emission from impurities, with the use of such lters, is more e ective. Silver foils have also been manufactured and used, but with unsatisfactory results due to the TBR-1 low plasma temperature. However, silver foils should be considered a good candidate for measuring T e through the absorbing method in large tokamaks with higher plasma temperatures.