AXIALISATION, COOLING AND QUENCHING OF BA+ IONS IN A PENNING TRAP

Collisions of ions, stored in a Penning trap, with neutral background molecules usually lead to rapid ion loss from the trap unless the ions are excited by tile sum of the frequencies of the reduced cyclotron a nd magnetron motion. Then the ions are cooled by collisions and are dr iven to the trap centre leading to substantial increase of the storage time. Furthermore in a three level system including a long living met astable state collisions deexcite this metastable state and increase t he population density in the ionic ground state. In a laser spectrosco pic experiment we demonstrate the advantages of collisions on Ba+ ions stored in a Penning trap. The combined action of metastable state que nching, axialisation and cooling leads to a significantly enhanced las er induced fluorescence signal. The cross section for collisional rela xation of the ground state Zeeman levels has been determined and we fi nd that it is of the same order of magnitude as quenching cross sectio n for a metastable state. Cooling and increased signal strength allows us to observe extremely narrow resonances and motional sidebands in m icrowave induced Zeeman transitions in the Ba+ electronic ground level .