Speaker
Description
The OEDO system was proposed to produce focused slow-down radioactive-ion (RI) beams in RIBF, and has been installed in the High-Resolution Beamline (HRB) in the end of fiscal year 2016.
Generally, the momentum dispersive focal plane has a strong correlation property between the pass point and the timing of the beam. The OEDO system was designed to tune separately energy degrading and beam focusing of the RI beams by using such a property of the dispersive focus. To obtain a mono-energetic beam, a wedge-shaped degrader on a dispersive focus is efficient tool. However a wide beam size at the dispersive focus become a defect to produce a small spot at a downstream focus for experimental measurements. We developed a new ion-optical scheme where the time-of-flight difference at the dispersive focus can be utilized for the beam focusing in parallel with use of a mono-energetic degrader for the beam-energy condensation.
The main components of the OEDO system are a Radio-Frequency deflector (RFD) synchronized with the accelerator cyclotron's RF and 2 sets of superconducting triplet quadrupole (STQ) magnets. The OEDO configures STQ-RFD-STQ on the straight beamline. At the entrance of the OEDO, the ion optics of HRB is tuned to be a momentum dispersive focus of approximately 10 mm/%, and a mono-energetic Al degrader is located there to slow down RIs to less than 50 MeV/u. The first STQ provides point-to-parallel transport, resulting in a strong correlation between the angular and time components of the beam. The second STQ works as inverse transformation of the first one. The RFD, locating in the middle of the two STQs, periodically changes the RI's horizontal angles in order to align them into parallel. The aligned RI's make a focus at the exit of the OEDO system through the parallel-to-point optics of the second half of the system.
The commissioning of the OEDO beamline has been performed in June, 2017 and we have successfully confirmed energy-degraded RI beams focused by the OEDO scheme.
In the commissioning run, we have produced long-lived fission products $^{79}$Se and $^{107}$Pd at around 40 MeV/u from a 345-MeV/u $^{238}$U beam. The slow-down $^{79}$Se beam obtained by the OEDO was at $45 \pm 2$ MeV/u, and its spot size at the secondary target position was 15 mm in FWHM.
In this presentation, we will show the details about the ion-optical design and about achieved performance of the OEDO system. We are also going to discuss upcoming physics experiments and physics plans developed at the OEDO beamline.
This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan).
