Left: Schematic of the ion source and rf-trap system. a- heated capillary; b- ion funnel; c- accumulation trap; d- octupole ion guide; e- gate valve; f- quadrupole mass filter; g- acceleration/deceleration stages; h- quadrupole deflector; i- cryogenic ring-electrode trap. Right: Photograph of the setup.

The Ion Source Laboratory consists of a beam line for single-pass experiments and tests of ion-production, accumulation, and cooling methods. In this system, ions are produced by e.g. electrospray ionization and guided through several differential pump stages by means of radio frequency multipole devices. There they are accumulated in a linear octupole ion trap in order to bunch the beam into pulses and then the ions are mass-to-charge ratio selected by the quadrupole mass filter. For experiments where internally cold ions are needed, the mass-selected ion bunch is bent 90 degrees into a cryogenically cooled section containing a ring electrode trap. In this trap, ions are stored for at least several milliseconds and are internally cooled by collisions with a 4K helium buffer gas. After the buffer gas has been pumped out, cold ion beam pulses are extracted and accelerated towards single pass experimental stations, as for instance an electrostatic analyzer for recording of fragment mass spectra from laser induced dissociation or from collisions in a cell filled with atomic or molecular gases.