The physics of impurity transport in response to a local gas injection in the scrape-off-layer (SOL) of Alcator C-Mod is investigated. Carbon "plumes'' are formed at variable locations in the SOL -- up to the separatrix -- by puffing deuterated ethylene gas (C2D4) through the end of a reciprocating fast-scanning probe. CCD cameras are used to simultaneously record C+1 and C+2 emission patterns from two near-perpendicular views. The plume dispersal patterns are found to yield direct qualitative information about plasma flow, including the direction of VExB near the separatrix. Impurity transport and plasma-surface interaction physics implicit in the 3-D plume structure is explored in detail using a Monte Carlo impurity transport code, with the aim of extracting background plasma-flow quantities. A number of important local effects involving plasma-probe interaction have been identified: a vertical ExB drift near the probe surface, a parallel electric field above the probe tip arising from plasma recycling off the probe surface, and sputtering of a carbon layer that dynamically forms on the probe surface. The emission patterns are also found to yield important information on flows in the SOL: radial electric field (Er) in the near SOL and volume-averaged values of the parallel Mach number in the far SOL. Er values obtained from plume data compare favorably with estimates of Er based on the poloidal propagation velocity of edge plasma fluctuations measured by the scanning probe. Comparisons between parallel Mach numbers obtained from the plume data and probe measurements indicate that the probe over-estimates the parallel flow towards the divertor in the far SOL. This result supports the picture of particle balance in the SOL of Alcator C-Mod being dominated by main-chamber recycling, with weak plasma flow into the divertor.

A Charge-Exchange Recombination Spectroscopy (CXRS) diagnostic has been installed on Alcator C-Mod to study the transport of light impurities in plasma. The system provides spatially (1 cm) and temporally (12.5 msec) resolved measurements of the impurity density, temperature and flow velocities of the particular impurity. Two optical arrays: poloidal (19 channels) and toroidal (10 channels), collect the light emitted from excited impurity ion populated by charge exchange process from the Diagnostic Neutral Beam (DNB) particle. The attention of this dissertation is focused on the B4 (n = 7 [-->] 6) spectral line emitted by B4 ion formed in the following charge exchange reaction (H0 + B5+ [-->] H+ + B4+*). A complex spectral model was developed to simulate emission. The high magnetic fields of C-Mod result in broad Zeeman patterns which must be taken into account for the interpretation of the line shift and broadening in terms of impurity ion velocity and temperature. After the spectral line fitting and careful identification of the charge exchange component, the calculated Doppler broadening and shifts of the spectral line profile yield information on the ion temperature and rotation. Together with the calculation of the beam density, the absolute calibration of the CXRS optical system provides us with B5+ density measurement capabilities. One of the main objectives of this work was to use the acquired impurity density, temperature and flow velocity profiles to investigate plasma transport behavior and infer the radial electric field E[subscript R] from plasma force balance equation. The focus here was placed on the region of the Internal Transport Barrier (ITB) formation 0.35