Antiproton Losses at Large Transverse Amplitudes in the CERN Antiproton Accumulator and Corrective Measures Using Skew Quadrupoles and Sextupoles

The CERN Antiproton Accumulator captures 3.5 GeV/c antiprotons with a nominal transverse acceptance of 100¿ mm. mrad in each plane. The transverse phase space population has been predicted by tracking antiprotons, created in the production target, through the transport line into the Accumulator. The predicted betatron amplitude distributions have been compared to those measured using internal scrapers in a zero momentum dispersion region. It is found that the antiproton population fits the predictions at low amplitudes, but for amplitudes beyond about half of the maximum values there is a progressive depopulation resulting in an overall shortfall in integrated antiproton yield by a factor of about two. This is attributed to the effects of linear and non-linear transverse coupling. After correction by skew quadrupoles and sextupoles the shortfall is reduced significantly but not entirely eliminated due to the practical difficulties in achieving complete compensation of the coupling forces.