Feasibility study into the use of mechanical choppers to alter the natural time structure of the APS

Abstract

In standard operating mode, the Advanced Photon Source (APS) is projected to be with 20 equally spaced bunches of positrons separated by 177 ns. This time structure may not be optimal for all experiments, particularly those experiments that require long periods (microseconds to milliseconds) of darkness preceding and/or succeeding the x-ray burst. As a result, an ongoing study is being made into the possibility of altering the natural time structure of the x-ray bursts from the APS. One possibility is through the use of fast kicker magnets (wobblers). A more passive approach is through the use of high-speed mechanical choppers. Using choppers rotating between 18 000 and 20 000 rpm (typical rotational speeds for currently operational neutron choppers), a single burst of x rays can be passed while blocking the surrounding bursts. Interpulse periods are adjustable from approximately 3 to 300 μs depending on the slit configuration of the chopper wheels. Even longer periods of darkness can be achieved by using phased choppers and/or mechanical shutters.