The experimental investigation of the formation of coherent structures in an electron beam of very low energy produced in a Malmberg‐Penning trap is presented. A rapid development of the structures is observed when, by increasing the emission current of the cathode, a sharp transition to a space charge dominated regime occurs, where a region unaccessible to beam electrons is found around the axis, and is characterized by a sharp density gradient at the edge. The transport of the structures along the beam is studied by varying the strength of the axial magnetic field. A 3D PIC simulation code is used to interpret the results. A modification of the configuration is under way, in which a pulsed electron source is used, and plasma effects in the beam transport, of relevance for X‐ray SASE‐FELs, can be investigated. © 2003 American Institute of Physics