A whole range of nuclei will be accessible for the first time for experiments at DESIR

Following the laying of the foundation stone on 10 November, the DESIR project is now taking shape at GANIL. Expected to be completed in 3 to 4 years’ time, this experimental hall will provide unprecedented resources for analysis, using exotic beams from the recently upgraded GANIL SPIRAL1 facility and its brand-new linear accelerator, LINAC SPIRAL2, through the new superconducting separator spectrometer S3. DESIR will provide extensive purification with state-of-the art instrumentation. Bertram Blank, the project’s scientific manager, tells us more about the project.

What new scientific opportunities will the DESIR project bring to GANIL?

DESIR is a new experimental hall that will complement GANIL’s experimental facilities for the study of exotic nuclei. Exotic nuclei are nuclei far from the stable nuclei on the nuclide map and they are very difficult to produce. Production with S3 will give access to nuclei of certain chemical elements, such as the refractory elements zirconium, niobium, molybdenum and many others, which are not produced at all in other laboratories, or only in very, very small quantities. This means that a whole range of nuclei will be accessible for the first time for experiments at DESIR, and this potential is based on two key factors: the diversity of GANIL’s beams and our ability to purify them prior to the experiments.

How does the diversity of GANIL’s beams play a key role?

To explore the full range of exotic nuclei, we need to use different production methods: fragmentation, fusion or fission of the existing nuclei. With GANIL’s various accelerators, it is possible to implement two of these methods: fragmentation, in the SPIRAL1 facility, using stable nuclei accelerated by GANIL’s original cyclotron accelerators, and fusion-evaporation in the SPIRAL2 S3 facility, using stable nuclei accelerated by SPIRAL2’s superconducting linear accelerator.

And why is the purification of these beams so important?

As with many experiments in existing facilities, the main problem is not so much the production of nuclei of scientific interest, but rather the simultaneous production of many contaminating nuclei, and hence the lack of purity of the beams made available to users. DESIR will therefore benefit from a purification chain that is unique of its kind, starting with a very high-resolution magnetic separator for this type of instrument. It consists of two powerful magnetic magnets coupled to other beam optics. It has a very high separation speed (a few microseconds). The next element in this purification chain will be a ‘MR-ToF’ type time-of-flight spectrometer, which is much slower than the magnetic separator (separation time of a few milli-seconds), but has a separation capacity 10 to 100 times
greater than the magnetic separator. The final element will be a separator consisting of a double Penning trap that will increase the separation power by another factor of 10 to 100, but the separation process will typically last 100 milli-seconds. These separation means are independent, but can also be coupled. In this way, each user can choose the separation means required for their experiment and benefit from ultra-pure beams. It is this separation chain that really sets DESIR apart from all the other facilities of this type in the world.

What about measuring instruments?

Various scientific collaborations will be setting up their experiments in the DESIR hall. Some of these experiments have already been developed and are in operation or commissioning in other European laboratories (Jyväskylä in Finland) or French laboratories (IJCLab in Orsay). Others are currently under construction. These instruments will be dedicated to mass measurements or measurements of angular correlations as part of the study of beta decay, grouped together under the name DETRAP, then experiments for laser spectroscopy grouped together under the name LUMIERE and finally instruments for the decay spectroscopy of exotic nuclei grouped together under the name BESTIOL. State-of-the-art equipment will thus be installed in DESIR, equipment that will obviously have benefited from the know-how of French nuclear physicists, engineers and technicians and their European and international colleagues.

Do these instruments have equivalents anywhere in the world? Is their design a technical feat?

A new research instrument is never an exact copy of another instrument, but is often inspired by existing instruments. It’s through national and international collaboration that new ideas and new instruments are born. And of course, we always try to do better than in the past, to take advantage of previous experience and also of new technical possibilities. For example, one of the beam ‘coolers’ used in DESIR will be able to ‘manage’ a factor of 10 to 100 more beam than its ‘brothers’ or ‘sisters’ elsewhere. A Penning double trap will also have a capacity 10 to 100 times greater than other equipment of the same type. Obviously, cutting-edge technical developments have been necessary to set up these instruments.

Will DESIR give France’s nuclear competitive edge to France’s nuclear research centre?

In any case, we’re doing everything we can to get there. I think that from an ‘equipment’ point of view we’ll be in a very good position. But the quality of the equipment available is only one of the conditions needed to create great experiences. It is now up to us to attract our French, European and international colleagues and to attract young talent to use our facilities. Obviously, our supervisory bodies must continue to support GANIL, SPIRAL2 and future projects. An important factor in the success of DESIR will be, for example, the construction of a new facility at GANIL
for the production of fission fragments. Such a facility was recently identified as the highest priority for GANIL beyond current projects by a committee of international experts.

How many countries and laboratories are contributing to its construction, and what are their different contributions?

The construction of DESIR is being carried out mainly by France via five nuclear physics laboratories belonging to IN2P3. GANIL’s contribution is obviously the most important, with the construction of the infrastructure and the preparation of its commissioning. Other laboratories are making essential contributions to the development of beam lines (IJCLab Orsay), purification facilities (LP2i Bordeaux and LPC Caen) and the identification and characterisation of beams sent to DESIR (IPHC Strasbourg). Others are developing experimental devices that will be installed in DESIR (SUBATECH Nantes). Other devices will be added to DESIR as part of collaborations with Germany, Spain, the United Kingdom and Belgium, to mention only the main European collaborators.

How was the project financed?

The final cost of the project, excluding extensions and contingencies, is 33 millions euros. Initial major funding of 9 millions euros was obtained by EQUIPEX DESIR as part of the Plan Investissement d’Avenir (now called France 2030) in 2011. This was followed in 2015 by major funding of 14 millions euros from Germany as part of a bilateral FAIR-SPIRAL2 agreement. GANIL’s supervisory bodies, the CNRS and CEA, and the local authorities, in particular the Normandy and New Aquitaine regions, have also made decisive contributions.

What is the roll-out schedule for this hall?

It’s a project that’s been around for a very long time. Initial discussions began in 2005. But a number of ‘events’ outside the project (postponement of part of SPIRAL2, changes in legislation, etc.) meant that the project slipped a long way behind schedule. Nevertheless, construction has now begun and the building is due to be delivered in full by mid-2025. The beamlines will then be installed, followed by the scientific equipment. The current plan calls for the first stable beam tests to be carried out by the end of 2026, and the facility to start up with the first scientific experiments using radioactive ion beams in 2027.