Resistive cooling of ions' center-of-mass energy in a Penning trap on millisecond time scales

We have performed systematic measurements of the resistive cooling behavior of bunches of highly charged ions in a Penning trap after injection from an external source. In particular, we have been able to measure the exponential cooling rate of the axial center -of -mass motion and experimentally show its linear dependence on the ion number within the bunch, as expected from theory. The common center -of -mass energy of the ions is reduced by more than four orders of magnitude on the time scale of milliseconds while the single -ion cooling occurs on the scale of seconds, representing a highly effective way to remove the dominating part of the ion kinetic energy.