A 60 Ghz Electron Cyclotron Resonance Ion Source for Pulsed Radioactive Ion Beam Production

The efficient production of short pulses of radioactive ion beams is a key point of the long term CERN betabeam project. A strong R&D effort in the field of ion sources is required to reach this challenging objective. A summary of the pulsed beta-beam ion source specification is proposed. A discussion follows on the ion source technologies suitable for this demanding project. The proposed solution foreseen (a 60 GHz ECRIS), uses a cusp magnetic configuration based on water cooled copper coils. The 3D magnetic field structure, along with the mechanical design status is presented. An experimental test with an aluminium prototype shows a good agreement with simulation and validates the design. THE BETA-BEAM PROJECT The neutrino physicist community is currently discussing the next generation neutrino beam factory. Nowadays, several projects are still under competition. The Beta-Beam is a project studied by the CERN [1]. The baseline scenario is to generate, ionize, and then accelerate Radioactive Ion Beams (RIB) ~5×10/s Ne or He to high energies (with a Lorentz factor γ>100). These nuclei which undergo a β decay are stored in a long race track decay ring to produce intense neutrino beams (see Figure1, blue arrows). The goal of these beams is to study the neutrino oscillations properties and give constraints on the mixing angle θ13. Figure 1: Baseline scenario of the beta-beam accelerator. The radioactive elements are expected to be produced in the future EURISOL facility. The primary beam, delivered by a proton LINAC, induces nuclear reactions in a set of target stations. Radioactive Gases effuse from the target to the ion source through a high conductance cooled pipe to filter gas and condensable contaminants. The ion source should bunch the beam in order to inject ions as efficiently as possible in the 3 synchrotrons rings included in the project. SPECIFICATIONS FOR THE PULSED ION SOURCE Pulsed Ion beam Current specifications Consider an ideal source able to ionize the RIB of interest with 100% efficiency. If the ion extraction is performed in continuous working (CW) operation, the 5×10 /s Ne flux would result in a 8 pμA extracted CW beam. Such ionic intensity is very easy to extract from a classical Electron Cyclotron Resonance Ion Source (ECRIS). The Beta-Beams pulse width at the source extraction is expected to be <50 μs, with a frequency repetition rate f=1/T ranging within the 10 to 25 Hz range. The highest peak current, derived from these values is ~16 pmA. Moreover, other gases will be extracted from the target and ionized in the source. Thus, an unknown number of contaminants will be added to the peak current. High radioactivity environment constraints The Ne and He half lives T1/2 are respectively 1.67s and 0.807s. The time for a radioactive atom to exit the target and reach a classical ion source located several meters away already approximately reduces the initial atoms flux by a factor 0.4. A key parameter for the project is to design an efficient ion source located as close as possible to the target in order to minimize the radioactive decay losses. Moreover, the source should hold radiation damages for a long time (~1 month). Consequently, the ion source mechanical parts shall not contain permanent magnets, plastic gaskets; even radiation damage on glass fibre may cause problems. Due to the high radiation level, the maintenance of the ion source will not be possible and its cost per unit will have to be moderate, since it may be necessary to change it periodically. Proceedings of ECRIS08, Chicago, IL USA TUCO-A03 Next Generation ECRIS