An ion implantation system has an ion source forming an ion beam. An mass analyzer defines and varies a mass analyzed beam along a beam path. A moveable mass resolving aperture assembly has a resolving aperture whose position is selectively varied in response to the variation of the beam path by the mass analyzer. A deflecting deceleration element positioned selectively deflects the beam path and selectively decelerate the mass analyzed beam. A controller selectively operates the ion implantation system in both a drift mode and decel mode. The controller passes the mass analyzed beam along a first path through the resolving aperture without deflection or deceleration in the drift mode and deflects and decelerates the beam along a second path in the decel mode. The position of the resolving aperture is selectively varied based on the variation in the beam path through the mass analyzer and the deflecting deceleration element.