Ion beam transport in gas-filled radio-frequency quadrupoles at intermediate pressures

Ion transport and focusing in radio-frequency (rf) quadrupole channels filled with a buffer gas at an intermediate pressure (100–1000 Pa) are studied theoretically through numerical simulation based on a combined model of ion-molecule interactions. The simulations uncovered specific effects that appear in the considered gas pressure range: “quasi-absolute” stability of motion of small-mass ions and radial boundedness of the ion focusing region.