Sideband cooling of ions in a non neutral buffer gas

We have investigated an extension of the buffer gas cooling technique to a non-neutral buffer gas. The
proposed scheme will allow efficient mass-selective centering of ions confined in a Penning trap in situations
where the use of a neutral damping agent is not possible. The present paper reviews the principle of the
technique and reports on evidence for sideband cooling of antiprotons in an electron gas, obtained with the
ATHENA apparatus at CERN’s Antiproton Decelerator facility.