Doppler measurements in the edge of the Alcator C-Mod tokamak using a high-resolution visible spectrometer

A versatile, high spectral resolution, transmission grating spectrometer appropriate for visible light (3500 - 6700 A) has been constructed and used for various spectroscopic plasma diagnostic applications at multiple facilities. The final characteristics of the spectrometer include a time resolution of 8 ms per spectra and an instrumental line width of 0.4 A (i.e. a resolving power, lambda/Deltalambda, of up to 14000 at 5780 A). There are 4 spatial channels which are fiber optically connected to the plasma source at a multitude of viewing geometry possibilities.;The diagnostic was fielded at the Alcator C-Mod tokamak located at the Plasma Science and Fusion Center at MIT. It has been used to investigate intrinsic plasma rotation and ion temperature profiles from Doppler shifts and broadening of both impurity and majority ion species during a multitude of plasma discharges. Most significantly, localized (via gas puff or diagnostic neutral beam), spatially and temporally resolved, Doppler measurements of the majority species at the inner and outer wall mid-plane have been obtained. Radial profiles of parallel flow at the inner wall is shown to match that derived from Mach probe based measurements in the various magnetic topologies available to diverted tokamak plasmas. Magnetic topology is found to have a strong influence on parallel plasma flows both in the scrape off layer (as has been known) and just inside the last closed magnetic flux surface. In experiments offering an abrupt topology change the affected parallel flow is followed from various species at multiple radial locations. The flow change is found to propagate from the edge to the core. This establishes the strong edge flow as an influential boundary condition, which has been linked to the L-H transition. It is suggested that the inner wall parallel flow is composed of a combination of outer wall ballooning transport driven flow and Pfirsch-Schluter flows.;Applications include Doppler velocity and temperature measurements of both impurity and majority ion species. The diagnostic was tested at the Compact Toroid Injection Experiment (CTIX) and the Sustained Spheromak Plasma Experiment (SSPX) at the Lawrence Livermore National Laboratory. Time resolved Doppler velocity measurements of multiple impurities (He II, O II and N II) and a high-resolution spectral survey from the CTIX plasma are given. A single point, time averaged toroidal rotation measurements from O III and Cl II emission were possible from the SSPX plasma.