Electron trapping in crossed electric and magnetic fields is an important mechanism by which electrical discharges can develop in low pressure gasses. We report observations of discharges produced by this mechanism around a spherical anode in two space simulation chambers, namely the Space Plasma Interaction Experiment (SPIE) at the University of Maryland, and the NASA-Lewis B-2 chamber. We have identified two types of discharges in these experiments. In the B-2 chamber, the breakdown takes the form of a runaway discharge with spherical topology, limited only by the ability of the power supply to provide the current. In the SPIE chamber this type of discharge also occurs, in addition to a low current toroidal discharge which is observed at higher magnetic fields. We present measurements of both types of discharge and show how the trapping effect of the magnetic field together with secondary electron emission by high energy ion bombardment of the chamber walls may initiate and sustains these discharges. ¿ Copyright 1990 by the American Geophysical Union