Speaker
Description
Most commonly, ISOLDE uses positively charged ion beams produced by a variety of ion sources such as the positive surface ion source, the Resonance Ionization Laser Ion Source (RILIS) or the Forced Electron Beam Induced Arc Discharge (FEBIAD) ion source. In recent years, the availability of negative ion beams at ISOLDE was re-established and the development program for negative ion sources was revitalized. Recently, the first measurement of the electron affinity of the isotope iodine-128 using the GANDALPH experimental beam line marked a milestone on the way to a first experimental determination of the electron affinity (EA) of the radioactive element astatine. During the first campaigns, it was evident that the astatine experiment would not be successful under the current conditions. The development program, presented here, addresses the issues from both sides: increasing the production efficiency of low affinity elements and improving the experimental setup.
To accelerate the negative ion source development, a dedicated ion source test stand was conceived and constructed. The two main features are an ion extraction system that allows measuring the total ion beam current, and a residual gas analyzer that allows us to monitor source degradation and outgassing. A data acquisition and control system facilitates the automation of repeated measurement tasks, thereby also enabling long-term performance tests, rigorous quality control and stress testing. Eventually we will perform destructive tests, which will give insight in to failure modes and operational limits, the lack of knowledge of which is often a limiting factor in achieving optimal ion source performance under on-line conditions.
The GANDALPH experimental setup is undergoing several upgrades in order to improve its suitability for the study of low intensity beams of negative radioactive astatine ions that are expected at ISOLDE. A dedicated off-line negative ion source has been designed which is to be coupled to the GANDALPH beamline. This will facilitate testing and fine-tuning of the neutral atom detector and the new electrostatic elements in the beam-line.
We will introduce the general concept of the GANDALPH experimental beam line and the envisioned measurements at ISOLDE. A detailed description of the ion source and its parameters will be given in addition to a summary of the first results obtained from the work at the new ion source test stand.
