Measuring and Manipulating an Accumulated Stack of Antiprotons in the CERN Antiproton Accumulator

The antiproton stack is observed through Schottky scans, both longitudinal and transverse. A particular feature is the wide dynamic range needed for observing both the dense core and the freshly-deposited tail. Separating batches of antiprotons from the stack (unstacking) is a highly automated process including the measurement of the momentum distribution and the generation of a suitable RF function to remove a slice of the desired density. Multiple slices may be removed successively and a process for locally flattening the distribution to obtain equal batch intensities is used. When successive batches are unstacked and ejected, the process may have to be aborted if the particles do not arrive correctly at the user. A "restack" facility is provided to return any antiprotons to the stack that have been unstacked but not ejected. A missing-bucket scheme for unstacking low-intensity batches for LEAR is also described.