Development of a LiF filter for plasma fluctuation measurements in the VUV spectral region
Anomalous transport of energy and particles in a tokamak is associated with fluctuations in plasma potential and in particle density. For research into this poorly understood phenomenon, transport across the separatrix into the edge plasma is of particular interest. A new diagnostic tool has been developed on ASDEX, which measures fluctuations in the intensity of impurity lines in the VUV region. A pinhole camera, incorporating LiF crystals as a cutoff filter, was used and the radiation intensity between two cutoff wavelengths (for filters at room temperature and at -60 C respectively) was measured. The signal differences were, however, far smaller than expected. A further problem was transmission loss, as the LiF filters gradually discoloured. This report describes a laboratory experiment aimed at establishing precisely how transmission behaviour of LiF is affected by temperature and radiation and by surface changes, and identifying the cause of the unsatisfactory results obtained so far. The diagnostic technique was also developed further. It was possible, for example, to restore the LiF crystals to full transmissivity by means of thermal annealing. Possible solutions for diagnostics with LiF on ASDEX-Upgrade were also proposed.
Bibliographic Reference: Report: IPP1/263 DE (1991) 79 pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 8046 Garching bei München (DE)
Record Number: 199111619 / Last updated on: 1994-12-02
Original language: de
Available languages: de