Cartoon of transformation of a wiggler to an undulator 

This animation is a cartoon of the radiation produced by a wiggler as an electron passes through its magnet array, followed by a reduction of the oscillation amplitude of the electron path until the individual radiation lobes overlap, resulting in the sharper and more intense radiation of an undulator. The cartoon is over-simplistic insofar that the transformation is not realised simply by reducing the amplitude, but also by reducing the periodicity of the magnet array. This added complexity seemed unnecessary here.