Collision Cooling of Ions Stored in Quadrupole Radio-Frequency Trap

We present a novel model for collisional energy transfer between ions and neutral molecules in the quadrupole radio-frequency trap. Calculated results quantitatively reproduce the dependence of the ion temperature T i on the buffer gas pressure P n , observed on Mg + ions and several collision partners (H 2 , He, and CH 4 ). It is deduced from the present model that T i is proportional to P n -1/3 in the low-pressure range below 10 -6 Torr, in good agreement with the experimental results.