Buffer-gas cooling of a single ion in a multipole radio frequency trap beyond the critical mass ratio

Understand

We theoretically investigate the dynamics of a trapped ion immersed in a spatially localized buffer gas.

• For a homogeneous buffer gas, the ion reaches a stable equilibrium only if the mass ratio of the buffer gas atom to the ion is below a critical value.
• We show how this limitation can be overcome by using multipole traps and a spatially confined buffer gas.
• Using a generalized model for elastic collisions of the ion with the buffer gas atoms, the ion's energy distribution is derived for arbitrary buffer gas distributions and trap parameters.