This component completely intercepts the x-ray photon beam via a fast-acting mechanism. It functions to isolate the downstream components from radiation. Closing time for the shutter is about one (1) second. The photon shutter acts as a safety device to protect the safety shutter (SS1) from direct beam impingement. Therefore, the photon shutter is interlocked to close before the closing of the safety shutters (to be discussed later). The position of the safety shutter is redundantly indicated in both up (open) and down (closed) positions.

The shutters of both PS1 and PS2 have the same configuration employing a “hockey stick” shaped copper absorber blade. The first photon shutter (PS1) serves as the traditional shutter in the front end and is interlocked to the front-end vacuum system. As such, it is acted upon during vacuum triggered shutdown events. The second photon shutter (PS2) is used exclusively by the experimenters and, as such, is very frequently actuated. This photon shutter, PS2, is the experimenter’s shutter for allowing beam into the First Optical Enclosure (FOE), i.e., the A-Station. Alarm points for PS1 include trips and faults on the PSS or faults on the Front-End Equipment Protection System (FEEPS). Faults and associated material shall be presented in Module A-7. The reader does not need knowledge of the details at this time.