Slow Extraction of Charged Ion Pulses from the REXEBIS

Abstract

The Isotope mass Separator On-Line DEvice (ISOLDE) facility located at CERN, produces and transports Radioactive Ion Beams (RIBs) at low or high energy through the REX/HIE-ISOLDE linear accelerator, for nuclear physics, astrophysics, solid-state physics and applied-physics purposes. Increasing the charge state of the ions is a prerequisite for efficient acceleration and is accomplished by an Electron Beam Ion Source (REXEBIS). For more effective event discrimination at the experimental detectors, such as the MINIBALL spectrometer, it is advantageous to increase the pulse width of extracted ions from this EBIS. A Slow Extraction scheme is presented which uses a function comprised of discrete voltage steps to apply the extraction potential to the EBIS trap barrier. This function effectively stretches the pulse length of both stable and radioactive ion beams, with different mass-to-charge ratios and provides for extracted pulse widths in the millisecond range. Key operational parameters of the EBIS impacting the average ionic temperature and its axial energy spread are discussed, in order to anticipate changes in the resulting ion pulse time structures during experimental runs.