Abstract
A novel phase contrast imaging is employed for diagnostics of plasma density fluctuations on LHD. With the use of two dimensional 48 ch (6×8) detector array and CO2 laser probe beam this technique permits observation of radial profiles of density fluctuation during a single discharge either within the entire plasma diameter in overview mode or within some fraction of the diameter in zoom mode. The velocity of density fluctuations in laboratory frame can be determined simultaneously with fluctuations of velocities. Analysis of system performance was made with the use of numerical calculations. The targets for the analysis include wave number and spatial resolution of the method, contrast of instrumental function, which is determined by low k signal leakage into the high k spectral region, and focal depth of the optical system for different fluctuation wave numbers. The role of shortcomings of optical system like distortion of the optical front by diffraction is studied. Suggestions for future upgrade of the diagnostics are advanced.
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