It lowers the temperature of a particle beam by reducing its energy dispersion and emittance, effectively increasing its brightness (brilliance).
The cooling must take place within a confining field in order to counteract the thermal diffusion that results from the ion-atom collisions.
Despite its long history, high-sensitivity high-accuracy mass measurements of atomic nuclei continue to be very important areas of research for many branches of physics.
At facilities such as ISOLDE at CERN and TRIUMF in Vancouver, for instance, measurement techniques are now being extended to short-lived radionuclei that only occur naturally in the interior of exploding stars.
Using a light neutral background gas, typically helium, charged particles originating from on-line mass separators undergo a number of soft collisions with the background gas molecules resulting in fractional losses of the ions' kinetic energy and a reduction of the ion ensemble's overall energy.