Listening to invisible waves on the JET tokamak | MIT News

Research scientist Alex Tinguely readjusts to Cambridge and Boston.

As a post-doctoral fellow at the Plasma Science and Fusion Center (PSFC), the MIT graduate has spent the past two years in Oxford, England, a city he recalls can be entirely traversed “in the time qu ‘it takes to walk from MIT to Harvard’. With its ancient stone walls, cathedrals, cobbled streets and winding paths, this small town was his home base for a big project: JETa tokamak which is currently the largest operating magnetic fusion energy experiment in the world.

Located at the Culham Center for Fusion Energy (CCFE), part of the UK Atomic Energy Authority, this key research center of the European Fusion program recently announced a historic success. Using a 50-50 deuterium-tritium fuel mixture for the first time since 1997, JET set a fusion power record of 10 megawatts in five seconds. It produced 59 megajoules of fusion energy, more than double the record of 22 megajoules set in 1997. As a member of the JET team, Tinguely oversaw the measurement and instrumentation (diagnostics) systems brought by the MIT group.

A lucky chance

The postdoctoral opportunity arose just as Tinguely was earning a doctorate in physics from MIT. Managed by Professor Miklos Porkolab as Principal Investigator for more than 20 years, this postdoctoral program has prepared several young researchers for careers in fusion facilities around the world. Collaborative research allowed Tinguely to work on a fusion device that would add tritium to the usual deuterium fuel.

Fusion, the process that powers the sun and other stars, could provide a long-term source of carbon-free energy on Earth, if it can be harnessed. For decades, researchers have tried to create an artificial star in a donut-shaped bottle, or “tokamak,” by using magnetic fields to keep turbulent plasma fuel confined and away from the walls of its container long enough for the merger to occur.

During his graduate studies at MIT, Tinguely worked on the now decommissioned PSFC Alcator C-Mod tokamak, which, like most magnetic fusion devices, used deuterium to create the plasmas for the experiments. JET, since commissioning in 1983, has done the same, later joining a small number of facilities that have added tritium, a radioactive isotope of hydrogen. While this addition increases the amount of fusion, it also creates a lot more radiance and activation.

Tinguely considers himself lucky to have been placed at JET.

“There aren’t many tokamaks in operation in the United States right now,” says Tinguely, “not to mention one that would run on deuterium-tritium (DT), which hasn’t been in operation for over 20 years, and that would make some really big measurements. I had a very lucky place where I was a post-doc at MIT, but I lived in Oxford, working on a very international project.

Scratch magnetic field lines

The measurements that interest Tinguely are low-frequency electromagnetic waves in tokamak plasmas. Tinguely uses antenna diagnostics developed by MIT, EPFL Swiss Plasma Center and CCFE to probe the so-called Alfvén eigenmodes when they are stable, before the energetic alpha particles produced by DT fusion plasmas can lead them to instability.

What makes MIT’s Alfvén Eigenmode Active Diagnostic essential is that without it, researchers cannot see or measure stable eigenmodes. Unstable modes show up clearly as magnetic fluctuations in the data, but stable waves are invisible without antenna prompting. These measurements help researchers understand the physics of Alfvén waves and their potential to degrade fusion performance, providing information that will be increasingly important for future DT fusion devices.

Tinguely compares the diagnosis to fingers on guitar strings.

“The magnetic field lines in the tokamak are like guitar strings. If you don’t have anything to energize the strings – or energize the waves of the magnetic field lines – they sit there, they do nothing. Energetic plasma particles can essentially “play guitar strings”, strum the magnetic field lines of the plasma, and that’s when you can see the waves in your plasma. But if the entrainment of the energetic particles of the waves is not strong enough, you will not see them, so you have to come and “strike the strings” with our antenna. And that’s how you learn information about the waves.

Much of Tinguely’s experience on JET took place during the Covid-19 pandemic, when offsite operations and analysis were the norm. However, because the MIT diagnostic had to be physically turned on and off, someone from Tinguely’s team had to be on site twice a day, a routine that became even less practical when tritium was introduced.

“When you have deuterium and tritium, you produce a lot of neutrons. Thus, certain buildings became prohibited during operation, which meant that they had to be switched on very early in the morning, around 6.30 am, and then switched off very late at night, around 10.30 pm.

To look forward

Now a researcher at the PSFC, Tinguely continues to work remotely at JET. He sometimes wishes he could take that train from Oxford to Culham again – fondly remembered for its clean and comfortable efficiency – to see work colleagues and visit local friends. The life he created for himself in England included training and performing with the 125-year-old Oxford Bach Choiras well as a weekly dinner service at The gatehousea facility that provides free support to local homeless and low-income communities.

“Being back is also exciting,” he says. “It’s fun to see how things have changed, how people and projects have grown, what new opportunities have arisen.”

In particular, he refers to a project that is beginning to take up more of his time: SPARC, the tokamak that the PSFC supports in collaboration with Commonwealth Fusion Systems. Designed to use deuterium-tritium to achieve net fusion gains, SPARC will be able to take advantage of the latest JET research. Tinguely is already exploring how his expertise with Alfvén’s own modes can support the experiment.

“I actually had the opportunity to do my PhD – or DPhil as they would call it – at Oxford University, but instead went to MIT for graduate study,” Tinguely reveals. “So it’s almost like a closure, in a way. I had my Oxford experience at the end, just in a different way, and I have the MIT experience as well.

He adds, “And I see myself being here at MIT for a while.”

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