Fluctuations and RF Measurements by Phase Contrast Imaging on Alcator C-Mod
Abstract
The Phase Contrast Imaging (PCI) system has been upgraded for fluctuations and RF measurements. For turbulence the line-integrated density fluctuations are measured along 12 vertical chords centered around the plasma axis. Two distinct modes have been observed, one coherent (exists only in H-mode) and one turbulent. Fourier analysis shows that both modes have well defined dispersion relations. For ICRF wave measurements an optical heterodyning system is used, where the laser beam is modulated slightly offset from the RF frequency and the low frequency detector array monitors the beat signal. We are also developing a computer simulation of the PCI system. Scalar diffraction analysis is used to model the system resolution by propagating the beam through the various apertures, lenses, phase plate and other system components. Recent upgrades include a new detector array, increased digitizer times, larger plasma access and the heterodyne configuration. We will present recent fluctuation measurements, the first ICRF measurements, and the system modeling results.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 1999
- Bibcode:
- 1999APS..DPP.KP141S