Positrons are used to cool antiprotons for the first time. The oppositely charged positrons and antiprotons are first simultaneously accumulated in separate Penning trap volumes, and then are spatially merged in a nested Penning trap. The antiprotons cool until they reach a low relative velocity with respect to the cold positrons, the situation expected to be optimal for the production of cold antihydrogen.

Phys. Lett. B

Gabrielse, G., Estrada, J., Tan, J. N., Yesley, P., Bowden, N. S., Oxley, P., … Hänsch, T. W. (2001). First positron cooling of antiprotons. Phys. Lett. B, 507(1-4), 1–6. doi:10.1016/S0370-2693(01)00450-6