  In the Alcator C-Mod tokamak, relativistic runaway electron (RE) generation
can occur during the flattop current phase of low density, diverted plasma
discharges. Due to the high toroidal magnetic field (B = 5.4 T), RE synchrotron
radiation is measured by a wide-view camera in the visible wavelength range
(~400-900 nm). In this paper, a statistical analysis of over one thousand
camera images is performed to investigate the plasma conditions under which
synchrotron emission is observed in C-Mod. In addition, the spatiotemporal
evolution of REs during one particular discharge is explored in detail via a
thorough analysis of the distortion-corrected synchrotron images. To accurately
predict RE energies, the kinetic solver CODE [Landreman et al 2014 Comput.
Phys. Commun. 185 847-855] is used to evolve the electron momentum-space
distribution at six locations throughout the plasma: the magnetic axis and flux
surfaces q = 1, 4/3, 3/2, 2, and 3. These results, along with the
experimentally-measured magnetic topology and camera geometry, are input into
the synthetic diagnostic SOFT [Hoppe et al 2018 Nucl. Fusion 58 026032] to
simulate synchrotron emission and detection. Interesting spatial structure near
the surface q = 2 is found to coincide with the onset of a locked mode and
increased MHD activity. Furthermore, the RE density profile evolution is fit by
comparing experimental to synthetic images, providing important insight into RE
spatiotemporal dynamics.
