RA1. RIB Development
(D. W. Stracener)
Significant progress has been made in the last few months on a number of ion source and target development projects. The efforts of the ISOL development group are devoted to developing techniques to improve the quality of radioactive ion beams at the HRIBF. The following is a summary of capabilities and recent activities at the facilities that are available at the HRIBF for testing RIB production targets and ion sources.
Ion Source Test Facility I (ISTF-1)
There are two facilities at the HRIBF where ion sources are developed. Operation of production ion sources on the RIB production platform has benefited greatly from the operational experiences gained at these facilities. Researchers at the ISTF-1 (including two summer students) have recently designed, installed, and tested an improved RFQ negative-ion beam cooler, which will be implemented at the new IRIS-2 production facility when it becomes available. This cooler is used in a beam purification technique where a laser interacts with a slow-moving ion beam and in specific cases where the electron affinities are favorable, unwanted negative ions are removed from the beam via photodetachment (see the August 2006 HRIBF Newsletter). This change in design will improve transmission through the cooler and allow it to be used with beams having energies that are typical of those from the ion source.
Ion Source Test Facility II (ISTF-2)
Development of an ion source based on resonant laser ionization using Ti:Sapphire lasers has been the primary focus of efforts at the ISTF-2 for the last few years. This project has been quite successful and the HRIBF laser ion source will be ready for utilization at the new IRIS-2 production platform. The laser system uses a Nd:YAG laser to pump three tunable Ti:Sapphire lasers, which provide the laser beams tuned to the frequencies needed to selectively ionize the atoms of interest. The last two Ti:Sapphire lasers have been ordered from Photonics and they should be delivered by October of this year. We are preparing to test the complete system with all HRIBF-owned lasers later this year.
On-Line Test Facility (OLTF)
At the OLTF, low intensity beams (up to 50 nA of 40-MeV protons) are available from the Tandem to irradiate RIB production targets. The separator at the OLTF was formerly known as the University Isotope Separator at Oak Ridge (UNISOR) where experiments with low-energy radioactive beams have been conducted since 1971. Recent efforts have focused on off-line testing of a novel ion source, which may result in purified beams of radioactive strontium isotopes. This source uses a quartz tube in the transfer line between the production target and the ion source to selectively slow down some elements such as rubidium and cesium. On-line characterization of this ion source was started in July and the analysis of the yield data has begun. Another recent on-line test measured the yields from a medium-density (6 g/cm3) uranium carbide target. The results are preliminary, but it appears that the beam intensities are lower than are extracted from the standard HRIBF uranium carbide targets, which have densities in the range of 1-2 g/cm3.
High Power Target Laboratory (HPTL)
High intensity production beams from ORIC are available at the HPTL to irradiate RIB production targets. This is the newest of the ISOL test facilities and will be co-located with the second RIB production platform (IRIS2). At the HPTL, we have begun off-line testing of a niobium silicide target coupled to a hot plasma ion source. In an upcoming on-line test, the yields of Al-25 and the short-lived isomer of Al-26 will be measured as a function of target temperature and production beam intensity. The yields of these radioactive aluminum isotopes will be compared to the measured yields extracted from previously-tested silicon carbide targets. These on-line tests have been delayed due to the installation of the high-voltage platforms and conduits for the IRIS2 project but we are now poised to take full advantage of the unique capabilities of the HPTL.