High dispersion spectrometer for time resolved Doppler measurements of impurity lines emitted during ISTTOK tokamak discharges

A high dispersion, multichannel, visible spectrometer has been developed for the ISTTOK tokamak, aiming at measuring the evolution of both the edge ion temperature and plasma poloidal velocity, by analysis of a CIII spectral line. It is based on a double monochromator configuration with two high ruling densities (2700 l/mm) and 1 m focal length concave diffraction gratings, a commercial double microchannel plate image intensifier, a fast (f/# = 1) relay lens built with two high diameter condensers in a back-to-back configuration, and a 2048 element photodiode charge coupled device optical multichannel analyzer. Laboratory tests have shown that a high dispersion has been achieved (approximate to1.65 Angstrom/mm), while keeping good temporal resolution (5 ins). Typical values measured for ion temperature (from Doppler broadening) were T-i congruent to 25 eV while for poloidal velocity (from Doppler shift) nu(theta)congruent to6 km/s. (C) 2003 American Institute of Physics.