The Magnetics and Radiation Sources (MaRS) group at ASTeC and the Low Energy Beams Group (LEBG) at ISIS have developed a permanent magnet dipole for charge state selection in a low-energy beamline of a novel carbon-free accelerator concept for Ion Beam Analysis. The work was funded from STFC’s Net Zero programme.
The magnetic field required for the ion beam selection can be produced with permanent magnets, which do not consume power but cannot be turned off either. Their use in low-energy beamlines for ion species selection has been hindered by the loss of versatility in comparison to electromagnets. This is especially true for ion beam analysis and nuclear physics facilities requiring a selection of ion beams, i.e. various elements and ion charge states, for elemental analysis of samples or nuclear physics experiments. The magnetic field of the new instrument can be adjusted by moving part of the permanent magnet structure, which makes the design appealing for Ion Beam Analysis (IBA) facilities, Low Energy Beam Transport (LEBT) of large-scale heavy ion accelerator facilities, and isotope separation systems, e.g. for precursors of medical isotopes.
The dipole magnet was built by STFC’s Technology Department, and its magnetic field was measured at Daresbury Laboratory. After passing the verification procedure where the field adjustment range of the magnet was confirmed, the device was sent to the JYFL accelerator laboratory (University of Jyväskylä, Finland), where the magnet was integrated into the low energy beamline of a prototype permanent magnet ion source. The CUBE-ECRIS is a novel permanent magnet ion source developed in collaboration between ISIS and JYFL. The first tests of the permanent magnet front-end, i.e. the high charge state ion source and LEBT developed for sustainable accelerator for IBA, were carried out in May 2024. These first experiments with argon ion beams demonstrated that IBA-relevant charge states and beam currents can be produced with the novel concept.
The next step towards a sustainable IBA facility is to build a 500 kV high voltage platform, accelerating highly charged argon ions to 3-6 MeV energies required for IBA of thin film samples revealing their elemental depth profiles. The platform and its acceleration column will be air-insulated, which eliminates the use of SF6 gas, which has 23,900 times “global warming potential” of CO2 and is used in all existing tandem-accelerators used for IBA.
The permanent magnet dipole field measurement at ASTeC’s Magnet Measurement Laboratory.
The prototype front-end of the sustainable IBA-facility. The CUBE-ECRIS permanent magnet ion source (left), the adjustable-field permanent magnet dipole (middle), and beam diagnostics (right).
