Simulations of injection optics for an RFQ cooler and buncher

This report is about injection of ions to a new RFQ (which stands for a Radio Frequency Quadrupole) cooler & trap which will be built at ISOLDE, CERN. This device brings very good advantages to existing beamline - for instance, lower emittance in transversal plane and lower energy spread in longitudinal direction. It will be possible to bunch the beam. Lower emittance means that ions can be focused to smaller spot thus improving precision of measurements. For laser experiments bunched beam is much more useful compared to continuous beam. Bunch can be adjusted such that lasers are synchronized with the ion bunch thus increasing signal-to-background ratio. Using buffer gas cooling is also very cost effective and easy to operate - there is only a few tunable parameters in the RFQ. Buffer gas cooling is effective only if ions are much heavier than the buffer gas. Usually this is the case at ISOLDE. One of the most crucial part in the whole RFQ project is the injection. Because of the presence of buffer gas, RF rods must be enclosed in a vessel that holds the buffer gas. To prevent buffer gas from reaching high vacuum areas, there is only narrow hole through which ions must pass. Because of this and deceleration of ions injection is not a straight forward procedure. At present, there exists several working RFQ coolers in the world many of which are in EXOTRAP collaboration. For instance, in Jyväskylä, Finland RFQ cooler is used as an injector to laser experiments and for injector to a Penning trap which requires very high quality beam. Simulations related to this report have been conducted at CERN during the summer 2002.