  Aims: Emission line profiles from solar coronal loops exhibit properties that
are unexplained by current models. We investigate the non-thermal broadening
associated with plasma heating in coronal loops that is induced by magnetic
field line braiding. Methods: We describe the coronal loop by a 3D
magnetohydrodynamic model of the turbulent decay of an initially-braided
magnetic field. From this we synthesize the Fe XII line at 193 Angstroms that
forms around 1.5 MK. Results: Key features of current observations of extreme
UV lines from the corona are reproduced in the synthesised spectra: (i) Typical
non-thermal widths range from 15 to 20 km/s. (ii) The widths are approximately
independent of the size of the field of view. (iii) There is a correlation
between line intensity and the non-thermal broadening. (iv) Spectra are found
to be non-Gaussian, with enhanced power in the wings of order 10-20%.
Conclusions: Our model provides an explanation that self-consistently connects
the heating process to the observed non-thermal line broadening. The
non-Gaussian nature of the spectra is a consequence of the non-Gaussian nature
of the underlying velocity fluctuations, interpreted as a signature of
intermittency in the turbulence.
