An ultrahigh vacuum system is described which was designed to study particles emitted from surfaces under bombardment by hydrogen ions. Stress has been laid on obtaining pressures ∼10−9Torr in the presence of the ion beam. The beam is mass analyzed and its energy is variable from 5 to 30 keV. A maximum current of 300 &mgr;A over 0.1 cm2is obtainable at the target, so that a beam/neutral gas bombardment ratio of better than 1000/1 can be achieved. A target mounting turntable is described which allows up to six targets to be bombarded in turn. A quadrupole mass filter is incorporated in the target chamber as a residual gas analyzer and as a means of identifying gas species resulting from the bombardment of surfaces.