Abstract: A system and method is described for obtaining a spatial characterization of a particle beam, including the beam direction, position, divergence, aberrations and intensity profile. A mechanism is also provided for adjusting the beam propagation to a desired state in response to the sensed characteristics. A fiber array in the path of a neutral particle beam casts shadows which are sensed at a downstream location to characterize the beam. Various mechanisms can be used to sense the shadow positions and/or widths relative to the fibers, from which the various beam characteristics can be derived. By magnetically removing charged particles from the neutral beam shadows, the shadows can be sensed by their effect upon the secondary emission currents generated in downstream conducting sensor wires, by their effect upon the fluorescence of downstream optical fibers, or by their effect upon the thermal heating of various types of downstream heat sensors.