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INJECTED BEAM IMAGING AT SPEAR 3 WITH A DIGITAL OPTICAL MASK

At SPEAR3, the 3GeV synchrotron light source operates in top-up injection mode with 273nC charge circulating in the storage ring (350mA). Each individual injection pulse contains only 40-80 pC, or a contrast ratio between stored to injected charge about 5000:1. In order to monitor injected beam dynamics during user operations, it is desirable to optically image the injected charge distribution on a turn-by-turn basis in the presence of the bright stored beam. The measurement is made by imaging the beam in visible synchrotron radiation onto a digital micro-mirror-array device (DMD) which is used to 'mask' light from the central stored beam while observing the weak injected beam signal on an image intensified, fast-gated CCD camera. Complex beam dynamics are observed after only a few tens of turns around the synchrotron. In this paper we report on the DMD optical configuration, masking considerations, measurement timing and initial tests imaging the injected beam in the presence of stored beam.