  Beam halo is an important factor in any high intensity accelerator. It can
cause difficulties in the control of the beam, emittance growth, particle loss
and even damage to the accelerator. It is therefore essential to understand the
mechanisms of halo formation and its dynamics in order to control and minimize
its effects. Experimental measurement of the halo distribution is an important
tool for such studies. In this paper, we present a new adaptive masking method
that we have developed to image beam halo, which uses a digital
micro-mirror-array device (DMD). This method has been thoroughly investigated
in the laboratory using laser and white light sources, and with real beams
produced by the University of Maryland Electron Ring (UMER). A high dynamic
range ~10(5) has been demonstrated with this new method and recent studies
indicate that this number can be exceeded for more intense beams by at least an
order of magnitude. The method is flexible, easy to setup and can be used at
any accelerator or light source. We present the results of our measurements of
the performance of the method and images of beam halos produced under various
experimental conditions.
