Plasma fluctuations in the scrape-off layer and at the divertor target in Alcator C-Mod and their relationship to divertor collisionality and density shoulder formation

•A combination of divertor rail Langmuir probes and midplane scanning probes were used to interrogate scrape-off layer fluctuations.•Increasing core averaged Greenwald fraction results in a clear density shoulder formation in the midplane profiles as per previous measurements.•In addition, fluctuations become more intermittent in the far scrape-off layer of both the divertor and the midplane.•Using nitrogen seeding in the divertor, the divertor plasma temperature is reduced and collisionality increases over two orders of magnitude at the strike point.•However, there appears to be little to no effect on midplane density profiles and far scrape-off layer fluctuation statistics.