MEASUREMENT OF VELOCITY FLUCTUATIONS IN PLASMAS BY A CONVENTIONAL VISIBLE SPECTROMETER

A conventional visible spectrometer system has been applied to velocit y fluctuation measurements in plasmas. By measuring the number of phot ons, the effect of quantum noise is subtracted, and real velocity fluc tuations are obtained. The first measurements in a reversed-held-pinch plasma show finite velocity fluctuations of about 1.7 x 10(3) m/s whe n the system views off-center chords. When it views the central chord, finite fluctuations are not found. These results impose an upper limi t to spurious Doppler broadening, which could arise from fast and larg e vibrations of cold plasma. The effect of the spurious Doppler broade ning is found to be small. (C) 1995 American Institute of Physics.