Chronos: New access mode for investigating slow processes

A volcano is erupting at the BM18 beamline. Not a real volcano of Krakatoan proportions,
 but something dynamically similar – an alumina vessel the size of a piece of chalk, part filled with synthetic rock. Suspended in the beamline well away from anything that is likely to catch fire, this model volcano is heated above 800°C until the rock melts, becoming a magma that bubbles and rises. Depending on the experimental conditions, the magma erupts with Hawaiian fluidity – or, as in Krakatoa, it explodes.

In real volcanoes, the precise conditions that result in an explosion rather than calm, “effusive” lava flow are highly contested. Studying his model at BM18, ESRF scientist Benoît Cordonnier has a major advantage in this debate, in that he can directly observe the dynamics of the processes leading to the eruption, in particular the key parameters of decompression rate and apparent magma viscosity. His results point towards new modes of decompression, never observed before, with the implication that explosive volcanoes can occur at lower rates of pressure drop than previously thought. Such insights are thanks partly to his novel volcano model, but also to the matchless flux of EBS X-rays, which are able to image much thicker apparatuses and samples of rock and magma than those of any other synchrotron. “We need to take more measurements, but so far we’re very enthusiastic about our results,” says Cordonnier. “What’s more, they’re attracting well-known European volcanological teams from Manchester in the UK to Camerino in Italy – they all want to use this instrumentation, too.”
 

Benoît Cordonnier’s model volcano at the BM18 beamline.

Still, there has been a limit to how accurately volcanoes can be modelled at synchrotrons, even for a skilled experimenter such as Cordonnier. Although eruptions can happen quickly, underlying geological conditions can develop over years – far longer than typical synchrotron experiments, which usually take place over a single six-month scheduling period. And volcanoes are not the only geological systems that present timing problems. Earthquakes – or more specifically, the fault-healing processes that occur post-quake to make an active zone dangerous again – also have characteristic timescales up to several years, if not centuries or millennia. So too do many processes and technologies related to climate change, from storing carbon dioxide underground to testing the longevity of rechargeable batteries over many charge–discharge cycles.

No rush

This is the motivation for Chronos, a new block allocation group (BAG) of independent principal investigators (PIs) who are all interested in long and slow processes. Coordinated by Cordonnier, together with Jessica McBeck, a geoscientist and computer scientist at the Norwegian University of Science and Technology of Trondheim who won the 2024 ESRF Young Scientist Award, Chronos allows PIs to perform experiments up to two years in duration by sharing beamtime among themselves in the most efficient manner. It is a type of community access that has long been used by structural biologists to maximize the rate of protein diffraction data that can be captured in a given timeframe, only here the emphasis is on establishing a new provision for the imaging of very slowly changing systems.

Chronos is the fourth new ESRF community-access BAG, following those for shock physics, 
historical materials and additive manufacturing. Although the way of working can take a while for PIs to get used to, the bigger challenge with the Chronos BAG is physical: how to operate numerous different experiments over long timeframes, without any one experimental set-up being disturbed?

This is where Cordonnier’s expertise comes in – although he insists he has no natural gift. “I played with Lego and Mechano when I was little, but so do a lot of kids,” he says. “And like a lot of people I get stressed trying to build IKEA furniture. It’s just that at some point early on I dedicated time to making experiments.” For Cordonnier, who trained as a volcanologist at the Ludwig Maximilians University of Munich in Germany in the late 2010s, that point came in a post-doctoral position at the University of California, Berkeley, in the US, where he first developed volcano analogues under synchrotron light. Later, at ETH Zurich in Switzerland, he used and maintained two of the Rock Deformation Laboratory’s legendary Paterson presses, which are capable of subjecting large samples to conditions equivalent to those in the first half of the Earth’s crust.

Now at the ESRF, he has turned his attention to the problem of how to continually mount and dismount apparatuses without losing alignment. His answer: magnets. The idea is not entirely new – think of the charging cables on Apple Macbooks and certain other laptops – but Cordonnier has shown that, when combined with references on the devices for small displacement corrections, a three-point magnetic mounting system can sustain a long-term precision of 10 μm. It will be used for all 11 projects that initially form the Chronos BAG at the BM18 and BM05 beamlines. “With more than one beamline, it turns out to be extremely flexible,” says Cordonnier. “The experiments can easily be interlaced with commissioning. Also, as they are all long-term runs, they don’t require precise timing and can be switched with other experimental shifts.”

It is too soon to tell what the results of this unique BAG will be. But Cordonnier points out that after he briefly mentioned it during a couple of talks, three attendees submitted proposals, and two others prepared to align projects backed by the European Research Council with the new capability. In this age of instant gratification, it may be reassuring to know that, in many research areas, the fastest route to new results is to take it slow. 
 

Text by Jon Cartwright

Top image: Postdoc Catherine Dore-Ossipyan (left) and scientist at BM18 Benoit Cordonnier (right)