RFQ
ion guides are special versions of a mass filter that operate in a buffer gas
environment in order to damp (cool) the ions’ axial and transverse motion.
In addition to the RF field needed for the confinement of ions a DC gradient
along the axis of the device is required to drag ions to the exit of the
device. This axial field is usually set up by segmenting the rods and applying
suitable voltages to the pieces. In the LEBIT project novel wedge-type
electrodes will be used that avoid segmentation.
For
accumulation and bunching of ions a portion of an RFQ ion guide can be
operated as a linear Paul trap. In this mode some segments near the end of the
ion guide form an axial potential depression where injected ions accumulate
(see figure). In order to eject ion bunches the voltages of the last segments
of the linear Paul trap are lowered sufficiently.