Target Ion Source for Short-Lived Ion Production – TULIP

The stable ion beams of GANIL range from carbon to uranium, and their energy covers the range from a few MeV/A to 100 MeV/A. This specificity offers possibilities for producing RIBs via cross-section-optimized nuclear reaction conditions, and facilitates the adaptation of the device design in terms of geometry, material, and principle to be implemented.

The final intensity of RIB results from the product of production in the target by the efficiency of transformation of atoms into ions (TAI). The originality of the approach lies in the fact of favoring TAI efficiency rather than the production of nuclei in the target. Once the optimal nuclear reaction is chosen, each mechanism involved in the TAI process is optimized, namely release outside of the nucleus-stopping material, release outside of the production cavity and ionization.

The releases of different carbon material structures, including carbon nano-tubes, were studied at the IJCLab (Orsay). Target developments for hostile environments and original technical combinations were developed and tested offline, during experiments on a test bench at GANIL. Once at the point, the systems were tested on-line, using GANIL beams and fusion-evaporation reactions. Each aspect of the project, nuclear reactions, targets, materials for the cavity, thermo-, mechanic- and electro-technologies were individually addressed and then gradually assembled during an experimental development program.

The release measurements of Rb atoms outside 4 carbon-based materials have been successfully conducted and have shown that the best structure of the catcher material is that of a carpet of small diameter nano-tubes (J. Guillot et al., NIM B 526 (2022) 9-18). In the case of 74Rb atoms, 82% of the nuclei should be relaxed. While waiting to dispose of this material, it will be replaced by a sheet of "graphite paper", outside of which 47% of the atoms of 74Rb are released (at a temperature of 1400 °C).

The production of ions 74 to 78Rb+ measured at the end of the reaction 20Ne@90MeV/A+nat58Ni is as expected, with an atom-to-ion transformation efficiency of about 10%.

The production of 74Rb+ ions was increased to several hundred ions/s using the reaction 20Ne@117MeV/A+nat58Ni, and a cavity temperature above 1500 °C (experiment 3-7 September 2025). The results must be analyzed in detail. They are already very promising and should still be significantly improved.

For these ions, the measured transformation time (~20 μs) is much lower than the lifetime of 74Rb (65 ms), and consistent with the transformation time measured offline prior to the project (P. Jardin et al., NIM A 1055 (2023)168332).

A minimum ionization efficiency of 10% for the stable elements Sn, In and Ag was measured under nominal operating conditions of the TULIP-FEBIAD device intended for the production of radioactive metal ions around 100Sn.

All of these results support the possibility of producing a beam of several ions/s of 100Sn+, the objective of the project.

At the end of the project, two devices for radioactive ion production were realized, TULIP for alkaline ions and TULIP-FEBIAD for metal ions. Their behavior has been made reliable to function stably during the minimum operating time in SPIRAL1. Their performance was measured using stable atoms on bench, and radioactive (74 to 78Rb+) in the case of the TULIP device for alkaline ions.

A rotating target has also been developed to increase the maximum intensity of the incident primary beams, thus the production rates up to a factor 7 while limiting the risk of damage induced by irradiation and high temperature.

A database on the diffusion of atoms in solids at high temperatures has been built up as well as an exploitation code (A. Ribet et al., doi.org/10.4028/p-u7wKGE).

A production target based on Mo and natural Ni has been achieved and proven (P. Jardin et al., doi.org/10.1051/epjconf/202328508001). Combined with different primary beams, it allows the production of a wide range of isotopes (around Rb and Sn so far).

A device for producing thin targets by electrodeposition has been built to provide other targets and extend the production range of neutron-deficient isotopes.

The performances of these target-source sets pave the way for ambitious experiments in subatomic physics at SPIRAL1/GANIL, as a preliminary to SPIRAL2/DESIR experiments targeting very exotic nuclei, observable only at the price of exceptional production efficiency.

In the short term, these devices will demonstrate that thanks to an optimization approach of the production process, it is possible to produce very exotic radioactive ions with competitive or even unmatched intensities. This demonstration was done first for the 74Rb+ ions in September 2025, whose intensity was greater than one hundred pps. The production of 100Sn+ metal ions, which will be tested during 2026, should be greater than 1 pps. These results will confirm the good-founded of the approach and will immediately pave the way for the production of many other isotopes thanks to the significant adaptability of the device and the variety of beams delivered by GANIL.

The advance taken by GANIL in mastering this technique ensures it to be for several years among the world leaders for the production of ions in the region of short-lived neutron-deficient isotopes.

In the longer term, mastering this technique could be transposed to an ISOL installation using the intense beams of the SPIRAL2 accelerator.

In the immediate future, it is envisaged to mix the TULIP technique and that of thick-target production devices to increase the intensity of production of intermediate life elements (on the order of seconds) such as 39Ca.

...coming soon

The study of exotic nuclei, or short-lived radioactive nuclear systems, is one of the main avenues of research with a high potential for discoveries worldwide, in modern physics. The production of these systems, in the form of ions, is an essential pre-requisite to advance our understanding of the subatomic world. The national flagship for radioactive ion beam production is the SPIRAL facility and the SPIRAL2 ESFRI roadmap project, based at the Grand Accélerateur National d’Ions Lourds (GANIL) in Caen [1]. The Target Ion Source for Short-Lived Isotope Production (TuLIP) project aims to enhance the near-term nuclear physics research possibilities by creating unique radioactive ion beams for ambitious subatomic experiments at GANIL. This collaborative effort between GANIL and the Institut de Physique Nucléaire in Orsay (IPN) will explore fusion-evaporation nuclear reactions in a new Target-Ion Source System, associated with innovative nano-structured materials specifically developed for nuclear physics research. In-beam tests of common R&D will be carried out using the accelerated tandem beams of the Transnational Access facility ALTO [2], at the IPN. This is a short-term project complementary to other on-going SPIRAL developments and could provide an essential stepping-stone to facilitate the launch of the emblematic research program dedicated to first observations of exotic nuclei.

The first prototype could make post-accelerated alkali radioactive ion beams for near-term experiments a reality by 2021, with low energy metallic beams by 2023 on success of a second R&D prototype. Selective laser-ionization will be investigated at ALTO in 2020 to explore metallic ion production with the first prototype. Results of this work will be openly presented at conferences and appear in peer-reviewed papers. It is expected to benefit a wide community of physicts and stimulate unique physics opportunities.

One of the most promising regions for new physics focusses on the unusual symmetry present in the 100Sn nucleus. This self-conjugate doubly magic nucleus, composed of 50 protons (Z) and 50 neutrons (N) is the most exotic symmetrical nucleus of this type that be created. We aim to produce short-lived radioactive metallic ions around N=Z=50, and this will be our marker of success.

[1] pro.ganil-spiral2.eu/spiral2
[2]http://ipnwww.in2p3.fr/installation-ALTO, ENSAR2 EU HORIZON2020, contrat n°654002