Important Milestone for REX-ISOLDE

The key to REX-ISOLDE is the process of accumulating and cooling unstable ions in a trap and then stripping them of electrons in a so-called charge breeder before accelerating them in a linear accelerator. The first part of this process is the job of REXTRAP, the largest particle trap of its kind, which was successfully tested in 1999 (Bulletin 49/99). Last week it was the turn of REXEBIS (Electron Beam Ion Source), which strips the ions of electrons, to be put through its paces. By increasing the charge of the ions by removing electrons, the length of the linear accelerator needed to accelerate the ions can be reduced, since higher charge means more acceleration per unit length. This will make REX-ISOLDE is a compact and cost-effective energy booster.
To test REXEBIS, stable potassium ions with charge +1 were produced and injected into REXTRAP where they were accumulated, bunched and cooled. From there, the ions were extracted and transported to REXEBIS, where they were bombarded by a beam of electrons, stripping them of some of their own electrons and increasing their charge. After a short time, the ions were extracted from REXEBIS and detected with a charge of +4.
A stable isotope was used for this first test. When REX-ISOLDE is running with unstable isotopes, however, speed will be of the essence since many of the most interesting isotopes are very short lived. In this test, the ions spent just 5 milliseconds inside REXEBIS, giving a powerful demonstration that the new device can work comfortably within its 20 milliseconds design goal. Moreover, since many of ISOLDE's unstable ions are produced in small quantities, only a modest current of potassium ions was used to simulate realistic operating conditions. The successful injection of a limited ion current gives much promise for the future, but the REX-ISOLDE team is careful to point out that much work remains before the high efficiency required is achieved.
The remaining link in the REX-ISOLDE chain is the accelerator itself, scheduled for commissioning later this year. When that is complete, REX-ISOLDE will provide physicists with multiple radioactive beams of exotic isotopes for a whole range of new experiments. Uncommon nuclear structures for isotopes far from stability will be mapped. Nuclear astrophysical processes important in the early Universe will be investigated. And in solid state physics, where surface implantation of ions plays an important role today, scientists will begin to explore the possibilities opened up by deep implantation. After several years of hard work REX-ISOLDE is nearing completion and an accelerated radioactive beam is expected before the end of the year. Then the real physics can start.