A pulsed drift cavity to capture 30 keV ion bunches at ground potential

To capture radioactive ion beams of tens of keV in an ion trap, the use of a pulsed drift cavity allows one to avoid placing the complete setup on a high voltage (HV) platform. By pulsing down the voltage on a long electrode while the ion bunch is inside it, the electric potential zero level can be shifted down over a range equal to the initial beam energy, thus allowing the ions to be captured in a trap at ground potential. The pulsed drift cavity of the WITCH setup, which is completely HV-platform free, is described here. It is demonstrated that bunched beams with energies of typically 30–60 keV, as will become available to all users at the ISOLDE facility after the installation of an RFQ buncher, can be transported over distances of tens of meters to the experiments and by means of a pulsed drift cavity directly be injected into a purification Penning trap. Simulation work showing the efficiency of such a system is discussed and tests showing the feasibility of such a system are presented. An estimate of the pulse down time is made from TOF spectra. An outlook on how the system can be improved is presented too.