<p>Two distinct operating modes have been observed during development and testing of a low-power iodine-fed Hall thruster. These modes, named “jet” and “bell”, are visually identified by the plasma plume appearance and are associated with different performance figures. Thruster integral metrics and plasma properties are inferred and discussed to identify the parameters triggering the mode transition. It is found that a relevant fraction of slow ions appears when the thruster operates in bell mode and that the extracted ion flux spatially features a more diffused structure. Analysis of discharge current temporal dynamics supports the hypothesis that broadening of the discharge ionization length is responsible for the plume mode transition.</p>