We have made a direct determination of the diffusion rates in a stored, coasting antiproton beam by observing the decay rates associated with beam echoes in the longitudinal plane. The beam echoes, similar to those observed in other fields of physics, are generated by a sequential impulse excitation at harmonics of the beam revolution frequency. The echo envelope follows a characteristic response which, however, can be modified by the presence of even a very weak scattering process, permitting a sensitive determination of the longitudinal diffusion rate in the beam.

• Received 6 June 1995

DOI:https://doi.org/10.1103/PhysRevLett.76.620