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UCLA FIR scattering

195 R-0

UCLA FIR scattering

The laser-based far-infrared scattering system (lambda=1.22 mm) on DIII-D has been upgraded by the addition of a backward wave oscillator or carcinotron. By supplying up to 300 mW at lambda=1.06 mm, the carcinotron  increases the scattered power and signal-to-noise ratio by more than ten times.  The carcinotron-based system will use an IF tracking system to simultaneously remove the excessive phase noise, frequency drift typical of high-frequency tubes, and the effects of frequency pulling. This should allow more reliable measurements of low-frequency asymmetric spectra under all discharge conditions. The local oscillator will be provided by a frequency doubled and locked klystron, to enable heterodyne detection of the scattered signal.