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Ask me anything: Raghavendra Srinivas – ‘Experimental physics is never boring’

What skills do you use every day in your job?

One of my favourite parts of being an atomic physicist is the variety. I get to work with lasers, vacuums, experimental control software, simulations, data analysis and physics theory.

As I’m transitioning to a more senior position, the skills I use have changed. Rather than doing most of the lab-based work myself, I now have a more supervisory role on some projects. I go to the lab when I can but it’s certainly different. I’m also teaching a second-year quantum mechanics course, which requires its own skillset. I try to use my experience to impart more of an experimental flavour. The field is now in an exciting place where we can not only think about experiments with single quantum systems, but actually do them.

It’s important to have the right structures in place to deliver complex projects with many moving parts

I also work part-time at a trapped-ion quantum computing company, Oxford Ionics, which has grown from about 20 to over 60 people since I started in 2021. Being involved in a team with so many people has taught me a lot about the importance of project management. It’s important to have the right structures in place to deliver complex projects with many moving parts. In addition, most of my company colleagues are also not physicists; it’s important to be able to communicate with people across a range of disciplines.

What do you like best and least about your job?

Experimental physics is never boring, as experiments always find new and wonderful ways to break: 90–99% of the time something needs fixing, but when it works it’s just magical.

I’ve been incredibly lucky to work with a fantastic group of people wherever I’ve been. Experimental physics cannot be done alone and I feel very privileged to work with colleagues who are passionate about what they do and have a wide variety of skills.

I also love the opportunities for outreach activities that my position affords me. Since I started at Oxford, I have led work placements as part of In2scienceUK and more recently helped start a week-long summer school for school students with the National Quantum Computing Centre. In many ways, I think promoting the idea that a career in quantum physics is accessible to anyone as long as they are willing to work hard is the most impactful work I can do.

I do dislike that as you spend longer in a field, more and more non-lab-based tasks creep into your calendar. I also find it difficult to switch between different tasks but that’s the price to pay for being involved in multiple projects.

What do you know today, that you wish you knew when you were starting out in your career?

It’s a difficult feeling for me to shake off even now, but when I started my career, I used to feel afraid to ask questions when I didn’t know something. I think it’s easy to fall into the trap of thinking it’s your fault, or that others will think less of you. However, I believe it’s better to see these instances as opportunities to learn rather than being embarrassed.

Scientifically, I think it’s also really important to be able to take a step back from the weeds of technical work and have an idea of the big-picture physics you’re trying to solve. I would have encouraged my past self to spend more time thinking deeply about physics, even beyond the field I was in. Just a couple of hours a week adds up over time without really taking away from other work.

It’s easy to pour yourself completely into a project, but it’s important to do this sustainably and avoid burnout

One last thing I’d tell my past self is to think about boundaries and find a healthy work-life balance. It’s easy to pour yourself completely into a project, but it’s important to do this sustainably and avoid burnout. Other aspects of life are important too.

Julia Sutcliffe: chief scientific adviser explains why policymaking must be underpinned by evidence

This episode of the Physics World Weekly podcast, features the physicist and engineer Julia Sutcliffe, who is chief scientific adviser to the UK government’s Department for Business and Trade.

In a wide-ranging conversation with Physics World’s Matin Durrani, Sutcliffe explains how she began her career as a PhD physicist before working in systems engineering at British Aerospace – where she worked on cutting-edge technologies including robotics, artificial intelligence, and autonomous systems. They also chat about Sutcliffe’s current role advising the UK government to ensure that policymaking is underpinned by the best evidence.

Eco-friendly graphene composite recovers gold from e-waste

A new type of composite material is 10 times more efficient at extracting gold from electronic waste than previous adsorbents. Developed by researchers in Singapore, the UK and China, the environmentally-friendly composite is made from graphene oxide and a natural biopolymer called chitosan, and it filters the gold without an external power source, making it an attractive alternative to older, more energy-intensive techniques.

Getting better at extracting gold from electronic waste, or e-waste, is desirable for two reasons. As well as reducing the volume of e-waste, it would lessen our reliance on mining and refining new gold, which involves environmentally hazardous materials such as activated carbon and cyanides. Electronic waste management is a relatively new field, however, and existing techniques like electrolysis are time-consuming and require a lot of energy.

A more efficient and suitable recovery process

Led by Kostya Novoselov and Daria Andreeva of the Institute for Functional Intelligent Materials at the National University of Singapore, the researchers chose graphene and chitosan because both have desirable characteristics for gold extraction. Graphene boasts a high surface area, making it ideal for adsorbing ions, they explain, while chitosan acts as a natural reducing agent, catalytically converting ionic gold into its solid metallic form.

While neither material is efficient enough to compete with conventional methods such as activated carbon on its own, Andreeva says they work well together. “By combining both of them, we enhance both the adsorption capacity of graphene and the catalytic reduction ability of chitosan,” she explains. “The result is a more efficient and suitable gold recovery process.”

High extraction efficiency

The researchers made the composite by getting one-dimensional chitosan macromolecules to self-assemble on two-dimensional flakes of graphene oxide. This assembly process triggers the formation of sites that bind gold ions. The enhanced extracting ability of the composite comes from the fact that the ion binding is cooperative, meaning that an ion binding at one site allows other ions to bind, too. The team had previously used similar methods in studies that focused on structures such as novel membranes with artificial ionic channels, anticorrosion coatings, sensors and actuators, switchable water valves and bioelectrochemical systems.

Once the gold ions are adsorbed onto the graphene surface, the chitosan catalyses the reduction of these ions, converting them from their ionic state into solid metallic gold, Andreeva explains. “This combined action of adsorption and reduction makes the process both highly efficient and environmentally friendly, as it avoids the use of harsh chemicals typically employed in gold recovery from electronic waste,” she says.

The researchers tested the material on a real waste mixture provided by SG Recycle Group SG3R, Pte, Ltd. Using this mixture, which contained gold in a residual concentration of just 3 ppm, they showed that the composite can extract nearly 17g/g of Au³⁺ ions and just over 6 g/g of Au⁺ from a solution – values that are 10 times larger than existing gold adsorbents. The material also has an extraction efficiency of above 99.5 percent by weight (wt%), breaking the current of limit of 75 wt%. To top it off, the ion extraction process is ultrafast, taking around just 10 minutes compared to days for other graphene-based adsorbents.

No applied voltage required

The researchers, who report their work in PNAS, say that the multidimensional architecture of the composite’s structure means that no applied voltage is required to adsorb and reduce gold ions. Instead, the technique relies solely on the chemisorption kinetics of gold ions on the heterogenous graphene oxide/chitosan nanoconfinement channels and the chemical reduction at multiple binding sites. The new process therefore offers a cleaner, more efficient and environmentally-friendly method for recovering gold from electronic waste, they add.

Flash heating technique extracts valuable metals from battery waste quickly and cheaply

While the present work focused on gold, the team say the technique could be adapted to recover other valuable metals such as silver, platinum or palladium from electronic waste or even mining residues. And that is not all: as well as e-waste, the technology might be applied to a wider range of environmental cleaning efforts, such as filtering out heavy metals from polluted water sources or industrial effluents. “It thus provides a solution for reducing metal contamination in ecosystems,” Andreeva says.

Other possible applications areas, she adds, include sustainable decarbonization and hydrogen production, low-dimensional building blocks for embedding artificial neural networks in hardware for neuromorphic computing and biomedical applications.

The Singapore researchers are now studying how to regenerate and reuse the composite material itself, to further reduce waste and improve the process’s sustainability. “Our ongoing research is focusing on optimizing the material’s properties, bringing us closer to a scalable, eco-friendly solution for e-waste management and beyond,” Andreeva says.

Cosmic antimatter could be created by annihilating WIMPs

Weakly interacting massive particles (WIMPs) are prime candidates for dark matter – but the hypothetical particles have never been observed directly. Now, an international group of physicists has proposed a connection between WIMPs and the higher-than-expected flux of antimatter cosmic rays detected by NASA’s Alpha Magnetic Spectrometer (AMS-02) on the International Space Station.

Cosmic rays are high-energy charged particles that are created by a wide range of astrophysical processes including supernovae and the violent regions surrounding supermassive black holes. The origins of cosmic rays are not fully understood so they offer physicists opportunities to look for phenomena not described by the Standard Model of particle physics. This includes dark matter, a hypothetical substance that could account for about 85% of the mass in the universe.

If WIMPs exist, physicists believe that they would occasionally annihilate when they encounter one another to create matter and antimatter particles. Because WIMPs are very heavy, it is possible that these annihilations create antinuclei – the antimatter version of nuclei comprising antiprotons and antineutrons. Some of these antinuclei could make their way to Earth and be detected as cosmic rays

Now, a trio of researchers in Spain, Sweden, and the US has done new calculations that suggest that unexpected antinuclei detections made by AMS-02 could shed light on the nature of dark matter. The trio is led by Pedro De La Torre Luque at the Autonomous University of Madrid.

Heavy antiparticles

According to the Standard Model of particle physics, antinuclei should be an extremely small component of the cosmic rays measured by AMS-02. However, excesses of antideuterons (antihydrogen-2), antihelium-3 and antihelium-4 have been glimpsed in data gathered by AMS-02.

In previous work, De La Torre Luque and colleagues explored the possibility that these antinuclei emerged through the annihilation of WIMPs. Using AMS-02 data, the team put new constraints on the hypothetical properties of WIMPs.

Now, the trio has built on this work. “With this information, we calculated the fluxes of antideuterons and antihelium that AMS-02 could detect: both from dark matter, and from cosmic ray interactions with gas in the interstellar medium,” De La Torre Luque says. “In addition, we estimated the maximum possible flux of antinuclei from WIMP dark matter.”

This allowed the researchers to test whether AMS-02’s cosmic ray measurements are really compatible with standard WIMP models. According to De La Torre Luque, their analysis had mixed implications for WIMPs.

“We found that while the antideuteron events measured by AMS-02 are well compatible with WIMP dark matter annihilating in the galaxy, only in optimistic cases can WIMPs explain the detected events of antihelium-3,” he explains. “No standard WIMP scenario can explain the detection of antihelium-4.”

Altogether, the team’s results are promising for proponents of the idea that WIMPs are a component of dark matter. However, the research also suggest that the WIMP model in its current form is incomplete. To be consistent with the AMS-02 data, the researchers believe that a new WIMP model must further push the bounds of the Standard Model.

“If these measurements are robust, we may be opening the window for something very exotic going on in the galaxy, that could be related to dark matter, says De La Torre Luque. But it could also reveal some unexpected new phenomenon in the universe”. Ultimately, the researchers hope that the precision of their antinuclei measurements could bring us a small step closer to solving one of the deepest, most enduring mysteries in physics.

The research is described in the Journal of Cosmology and Astroparticle Physics.

First look at prototype telescope for the LISA gravitational-wave mission

NASA has released the first images of a full-scale prototype for the six telescopes that will be included in the €1.5bn Laser Interferometer Space Antenna (LISA) mission.

Expected to launch in 2035 and operate for at least four year, LISA is a space-based gravitational-wave mission led by the European Space Agency.

It will comprise of three identical satellites that will be placed in an equilateral triangle in space, with each side of the triangle being 2.5 million kilometers – more than six times the distance between the Earth and the Moon.

The three craft will send infrared laser beams to each other via twin telescopes in the satellites. The beams will be sent to free-floating golden cubes – each slightly smaller than a Rubik’s cube — that are placed inside the craft.

The system will be able to measure the separation between the cubes down to picometers, or trillionths of a meter. Such subtle changes in the distances between the measured laser beams will indicate the presence of a gravitational wave.

The prototype telescope, dubbed the Engineering Development Unit Telescope, was manufactured and assembled by L3Harris Technologies in Rochester, New York.

It is made entirely from an amber-coloured glass-ceramic called Zerodur, which has been manufactured by Schott in Mainz, Germany. The primary mirror of the telescopes is coated in gold to better reflect the infrared lasers and reduce heat loss.

On 25 January ESA’s Science Programme Committee formally approved the start of construction of LISA.

Orbital angular momentum monopoles appear in a chiral crystal

Magnets generally have two poles, north and south, so observing something that behaves like it has only one is extremely unusual. Physicists in Germany and Switzerland have become the latest to claim this rare accolade by making the first direct detection of structures known as orbital angular momentum monopoles. The monopoles, which the team identified in materials known as chiral crystals, had previously only been predicted in theory. The discovery could aid the development of more energy-efficient memory devices.

Traditional electronic devices use the charge of electrons to transfer energy and information. This transfer process is energy-intensive, however, so scientists are looking for alternatives. One possibility is spintronics, which uses the electron’s spin rather than its charge, but more recently another alternative has emerged that could be even more promising. Known as orbitronics, it exploits the orbital angular momentum (OAM) of electrons as they revolve around an atomic nucleus. By manipulating this OAM, it is in principle possible to generate large magnetizations with very small electric currents – a property that could be used to make energy-efficient memory devices.

Chiral topological semi-metals with “built-in” OAM textures

The problem is that materials that support such orbital magnetizations are hard to come by. However, Niels Schröter, a physicist at the Max Planck Institute of Microstructure Physics in Halle, Germany who co-led the new research, explains that theoretical work carried out in the 1980s suggested that certain crystalline materials with a chiral structure could generate an orbital magnetization that is isotropic, or uniform in all directions. “This means that the materials’ magnetoelectric response is also isotropic – it depends solely on the direction of the injected current and not on the crystals’ orientation,” Schröter says. “This property could be useful for device applications since it allows for a uniform performance regardless of how the crystal grains are oriented in a material.”

In 2019, three experimental groups (including the one involved in the latest work) independently discovered a type of material called a chiral topological semimetal that seemed to fit the bill. Atoms in these semimetals are arranged in a helical pattern, which produces something that behaves like a solenoid on the nanoscale, creating a magnetic field whenever an electric current passes through it.

The advantage of these materials, Schröter explains, is that they have “built-in” OAM textures. What is more, he says the specific texture discovered in the most recent work – an OAM monopole – is “special because the magnetic field response can be very large – and isotropic, too”.

Visualizing monopoles

Schröter and colleagues studied chiral topological semimetals made from either palladium and gallium or platinum and gallium (PdGa or PtGa). To understand the structure of these semimetals, they directed circularly polarized X-rays from the Swiss Light Source (SLS) onto samples of PdGa and PtGa prepared by Claudia Felser’s group at the Max Planck Institute in Dresden. In this technique, known as circular dichroism in angle-resolved photoemission spectroscopy (CD-ARPES), the synchrotron light ejects electrons from the sample, and the angles and energies of these electrons provide information about the material’s electronic structure.

“This technique essentially allows us to ‘visualize’ the orbital texture, almost like capturing an image of the OAM monopoles,” Schröter explains. “Instead of looking at the reflected light, however, we observe the emission pattern of electrons.” The new monopoles, he notes, reside in momentum (or reciprocal) space, which is the Fourier transform of our everyday three-dimensional space.

Complex data

One of the researchers’ main challenges was figuring out how to interpret the CD-ARPES data. This turned out to be anything but straightforward. Working closely with Michael Schüler’s theoretical modelling group at the Paul Scherrer Institute in Switzerland, they managed to identify the OAM textures hidden within the complexity of the measurement figures.

Contrary to what was previously thought, they found that the CD-ARPES signal was not directly proportional to the OAMs. Instead, it rotated around the monopoles as the energy of the photons in the synchrotron light source was varied. This observation, they say, proves that monopoles are indeed present.

The findings, which are detailed in Nature Physics, could have important implications for future magnetic memory devices. “Being able to switch small magnetic domains with currents passed through such chiral crystals opens the door to creating more energy-efficient data storage technologies, and possibly also logic devices,” Schröter says. “This study will likely inspire further research into how these materials can be used in practical applications, especially in the field of low-power computing.”

The researchers’ next task is to design and build prototype devices that exploit the unique properties of chiral topological semimetals. “Finding these monopoles has been a focus for us ever since I started my independent research group at the Max Planck Institute for Microstructure Physics in 2021,” Schröter tells Physics World. The team’s new goal, he adds, is to “demonstrate functionalities and create devices that can drive advancements in information technologies”.

To achieve this, he and his colleagues are collaborating with partners at the universities of Regensburg and Berlin. They aim to establish a new centre for chiral electronics that will, he says, “serve as a hub for exploring the transformative potential of chiral materials in developing next-generation technologies”.

On the proper use of a Warburg impedance

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Recent battery papers commonly employ interpretation models for which diffusion impedances are in series with interfacial impedance. The models are fundamentally flawed because the diffusion impedance should be part of the interfacial impedance. A general approach is presented that shows how the charge-transfer resistance and diffusion resistance are functions of the concentration of reacting species at the electrode surface. The resulting impedance model incorporates diffusion impedances as part of the interfacial impedance.

A Q&A session follows the presentation.

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Mark Orazem obtained his BS and MS degrees from Kansas State University and his PhD in 1983 from the University of California, Berkeley. In 1983, he began his career as assistant professor at the University of Virginia, and in 1988 joined the faculty of the University of Florida, where he is Distinguished Professor of Chemical Engineering and Associate Chair for Graduate Studies. Mark is a fellow of The Electrochemical Society, International Society of Electrochemistry, and American Association for the Advancement of Science. He served as President of the International Society of Electrochemistry and co-authored, with Bernard Tribollet of the Centre national de la recherche scientifique (CNRS), the textbook entitled Electrochemical Impedance Spectroscopy, now in its second edition. Mark received the ECS Henry B. Linford Award, ECS Corrosion Division H. H. Uhlig Award, and with co-author Bernard Tribollet, the 2019 Claude Gabrielli Award for contributions to electrochemical impedance spectroscopy. In addition to writing books, he has taught short courses on impedance spectroscopy for The Electrochemical Society since 2000.

Multi-qubit entangled states boost atomic clock and sensor performance

Frequency measurements using multi-qubit entangled states have been performed by two independent groups in the US. These entangled states have correlated errors, resulting in measurement precisions better than the standard quantum limit. One team is based in Colorado and it measured the frequency of an atomic clock with greater precision than possible using conventional methods. The other group is in California and it showed how entangled states could be used in quantum sensing.

Atomic clocks are the most accurate timekeeping devices we have. They work by locking an ultraprecise, frequency comb laser to a narrow linewidth transition in an atom. The higher the transition’s frequency, the faster the clock ticks and the more precisely it can keep time. The clock with the best precision today is operated by Jun Ye’s group at JILA in Boulder, Colorado and colleagues. After running for the age of the universe, this clock would only be wrong by 0.01 s.

The conventional way of improving precision is to use higher-energy, narrower transitions such as those found in highly charged ions and nuclei. These pose formidable challenges, however, both in locating the transitions and in producing stable high-frequency lasers to excite them.

Standard quantum limit

An alternative is to operate existing clocks in more sophisticated ways. “In an optical atomic clock, you’re comparing the oscillations of an atomic superposition with the frequency of a laser,” explains JILA’s Adam Kaufman, “At the end of the experiment, that atom can only be in the excited state or in the ground state, so to get an estimate of the relative frequencies you need to sample that atom many times, and the precision goes like one over the square root of the number of samples.” This is the standard quantum limit, and is derived from the assumption that the atoms collapse randomly, producing random noise in the frequency estimate.

If, however, multiple atoms are placed into a Greenberger–Horne–Zeilinger (GHZ) entangled state and measured simultaneously, information can be acquired at a higher frequency without increasing the fundamental frequency of the transition. JILA’s Alec Cao explains, “Two atoms in a GHZ state are not just two independent atoms. Both the atoms are in the zero state, so the state has an energy of zero, or both the atoms are in the upper state so it has an energy of two. And as you scale the size of the system the energy difference increases.”

Unfortunately the lifetime of a GHZ state is inversely proportional to its size. Therefore, though precision can be acquired in a shorter time, the time window for measurement also drops, cancelling out the benefit. Mark Saffman of the University of Wisconsin-Madison explains, “This idea was suggested about 20 years ago that you could get around this by creating GHZ states of different sizes, and using the smallest GHZ state to measure the least significant bit of your measurement, and as you go to larger and larger GHZ states you’re adding more significant bits to your measurement result.”

In the Colorado experiment, Kaufman, Cao and colleagues used a novel, multi-qubit entangling technique to create GHZ states of Rydberg atoms in a programmable optical tweezer lattice. A Rydberg atom is an atom with one or more electrons in a highly-excited state. They showed that, when interrogated for short times, four-atom GHZ states achieved higher precisions than could be achieved with the same number of uncorrelated atoms. They also constructed gates of up to eight qubits. However, owing to their short lifetimes, they were unable to beat the standard quantum limit with these.

Cascade of GHZ qubits

The Colorado team therefore constructed a cascade of GHZ qubits of increasing sizes, with the largest containing eight atoms. They showed that the fidelity achieved by the cascade was superior to the fidelity achieved by a single large GHZ qubit. Cao compares this to using the large GHZ state on a clock as the second hand while progressively smaller states act as the minute and hour hands. The team did not demonstrate higher phase sensitivity than could theoretically be achieved with the same number of unentangled atoms, but Cao says this is simply a technical challenge.

Meanwhile in California, Manuel Endres and colleagues at Caltech also used GHZ states to do precision spectroscopy on the frequency of an atomic clock using Rydberg atoms in an optical tweezer array. They used a slightly different technique for preparing the GHZ states. This did not allow them to prepare such large GHZ states as their Coloradan counterparts, although Endres argues that their technique should be more scalable. The Caltech work, however, focused on mapping the output data onto “ancilla” qubits and demonstrating a universal set of quantum logic operations.

“The question is, ‘How can a quantum computer help you for a sensor?’” says Endres. “If you had a universal quantum computer that somehow produced a GHZ state on your sensor you could improve the sensing capabilities. The other thing is to take the signal from a quantum computer and do quantum post-processing on that signal. The vision in our [work] is to have a quantum computer integrated with a sensor.”

Saffman, who was not involved with either group, praises the work of both teams. He congratulates the Coloradans for setting out to build a better clock and succeeding – and praises the Californians for going in “another direction” with their GHZ states. Saffman says he would like to see the researchers produce larger GHZ states and show that such states can not only confer an improvement on a clock with the same limitations as a similar clock measured with random atoms, but can produce the world’s best clock overall.

The research is described in two papers in nature Nature (California paper, Colorado paper).

Gems from the Physics World archive: Isaac Asimov

Cartoon illustration of Isaac Asimov — (Courtesy: Shutterstock/Mei-Zendra)

Since 1988 Physics World has boasted among its authors some of the most eminent physicists of the 20th and 21st centuries, as well as some of the best popular-science authors. But while I am, in principle, aware of this, it can still be genuinely exciting to discover who wrote for Physics World before I joined the team in 2011. And for me – a self-avowed book nerd – the most exciting discovery was an article written by Isaac Asimov in 1990.

Asimov is best remembered for his hard science fiction. His Foundation trilogy (1951–1953) and decades of robot stories first collected in I, Robot (1950) are so seminal they have contributed words and concepts to the popular imagination, far beyond actual readers of his work. If you’ve ever heard of the Laws of Robotics (the first of which is that “a robot shall not harm a human, or by inaction allow a human to come to harm”), that was Asimov’s work.

I was introduced to Asimov through what remains the most “hard physics”-heavy sci-fi I have ever tackled: The Gods Themselves (1972). In this short novel, humans make contact with a parallel universe and manage to transfer energy from a parallel world to Earth. When a human linguist attempts to communicate with the “para-men”, he discovers this transfer may be dangerous. The narrative then switches to the parallel world, which is populated by the most “alien” aliens I can remember encountering in fiction.

Underlying this whole premise, though, is the fact that in the parallel world, the strong nuclear force, which binds protons and neutrons together, is even stronger than it is in our own. And Asimov was a good enough scientist that he worked into his novel everything that would be different – subtly or significantly – were this the case. It’s a physics thought experiment; a highly entertaining one that also encompasses ethics, astrobiology, cryptanalysis and engineering.

Of course, Asimov wrote non-fiction, too. His 500+ books include such titles as Understanding Physics (1966), Atom: Journey Across the Subatomic Cosmos (1991) and the extensive Library of the Universe series (1988–1990). The last two of these even came out while Physics World was being published.

So what did this giant of sci-fi and science communication write about for Physics World?

It was, of all things, a review of a book by someone else: specifically, Think of a Number by Malcolm E Lines, a British mathematician. Lines isn’t nearly so famous as his reviewer, but he was still writing popular-science books about mathematics as recently as 2020. Was Asimov impressed? You’ll have to read his review to find out.

Negative triangularity tokamaks: a power plant plasma solution from the core to the edge?

The webinar is directly linked with a special issue of Plasma Physics and Controlled Fusion on Advances in the Physics Basis of Negative Triangularity Tokamaks; featuring contributions from all of the speakers, and many more papers from the leading groups researching this fascinating topic.

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In recent years the fusion community has begun to focus on the practical engineering of tokamak power plants. From this, it became clear that the power exhaust problem, extracting the energy produced by fusion without melting the plasma-facing components, is just as important and challenging as plasma confinement. To these ends, negative triangularity plasma shaping holds unique promise.

Conceptually, negative triangularity is simple. Take the standard positive triangularity plasma shape, ubiquitous among tokamaks, and flip it so that the triangle points inwards. By virtue of this change in shape, negative triangularity plasmas have been experimentally observed to dramatically improve energy confinement, sometimes by more than a factor of two. Simultaneously, the plasma shape is also found to robustly prevent the transition to the improved confinement regime H-mode. While this may initially seem a drawback, the confinement improvement can enable negative triangularity to still achieve similar confinement to a positive triangularity H-mode. In this way, it robustly avoids the typical difficulties of H-mode: damaging edge localized modes (ELMs) and the narrow scrape-off layer (SOL) width. This is the promise of negative triangularity, an elegant and simple path to alleviating power exhaust while preserving plasma confinement.

The biggest deficiency is currently uncertainty. No tokamak in the world is designed to create negative triangularity plasmas and it has received a fraction of the theory community’s attention. In this webinar, through both theory and experiment, we will explore the knowns and unknowns of negative triangularity and evaluate its future as a power plant solution.

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left to right: Justin Ball, Alessandro Balestri, Andrew “Oak” Nelson, Tim Happel, Haley Wilson, Olivier Sauter

Justin Ball (chair) is a research scientist at the Swiss Plasma Center at EPFL in Lausanne, Switzerland. He earned his Masters from MIT in 2013 and his PhD in 2016 at Oxford University studying the effects of plasma shaping in tokamaks, for which he was awarded the European Plasma Physics PhD Award. In 2019, he and Jason Parisi published the popular science book, The Future of Fusion Energy. Currently, Justin is the principal investigator of the EUROfusion TSVV 2 project, a ten-person team evaluating the reactor prospects of negative triangularity using theory and simulation.

Alessandro Balestri is a PhD student at the Swiss Plasma Center (SPC) located within the École Polytechnique Fédérale de Lausanne (EPFL). His research focuses on using experiments and gyrokinetic simulations to achieve a deep understanding on how negative triangularity reduces turbulent transport in tokamak plasmas and how this beneficial effect can be optimized in view of a fusion power plant. He received his Bachelor and Master degrees in physics at the University of Milano-Bicocca where he carried out a thesis on the first gyrokinetic simulations for the negative triangularity option of the novel Divertor Tokamak Test facility.

Andrew “Oak” Nelson is an associate research scientist with Columbia University where he specializes in negative triangularity (NT) experiments and reactor design. Oak received his PhD in plasma physics from Princeton University in 2021 for work on the H-mode pedestal in DIII-D and has since dedicated his career to uncovering mechanisms to mitigate the power-handling needs faced by tokamak fusion pilot plants. Oak is an expert in the edge regions of NT plasmas and one of the co-leaders of the EU-US Joint Task Force on Negative Triangularity Plasmas. In addition to NT work, Oak consults regularly on various physics topics for Commonwealth Fusion Systems and heads several fusion-outreach efforts.

Tim Happel is the head of the Plasma Dynamics Division at the Max Planck Institute for Plasma Physics in Garching near Munich. His research centres around turbulence and tokamak operational modes with enhanced energy confinement. He is particularly interested in the physics of the Improved Energy Confinement Mode (I-Mode) and plasmas with negative triangularity. During his PhD, which he received in 2010 from the University Carlos III in Madrid, he developed a Doppler backscattering system for the investigation of plasma flows and their interaction with turbulent structures. For this work, he was awarded the Itoh Prize for Plasma Turbulence.

Haley Wilson is a PhD candidate studying plasma physics at Columbia University. Her main research interest is the integrated modelling of reactor-class tokamak core scenarios, with a focus on highly radiative, negative triangularity scenarios. The core modelling of MANTA is her first published work in this area, but her most recent manuscript submission expands the MANTA study to a broader operational space. She was recently selected for an Office of Science Graduate Student Research award, to work with Oak Ridge National Laboratory on whole device modelling of negative triangularity tokamaks using the FREDA framework.

Olivier Sauter obtained his PhD at CRPP-EPFL, Lausanne, Switzerland in 1992, followed by post-doc at General Atomics in 1992-93 and ITER-San Diego (1995/96), leading to the bootstrap current coefficients and experimental studies on Neoclassical tearing modes. He has been JET Task Force Leader, Eurofusion Research Topic Coordinator and recipient of the 2013 John Dawson Award for excellence in plasma physics research and nominated since 2016 as ITER Scientist Fellow in the area of integrated modelling. He is a senior scientist at SPC-EPFL, supervising several PhD theses, and active with AUG, DIII-D, JET, TCV, WEST focusing on real-time simulations and negative triangularity plasmas.

About this journal

Plasma Physics and Controlled Fusion is a monthly publication dedicated to the dissemination of original results on all aspects of plasma physics and associated science and technology.

Editor-in-chief: Jonathan Graves University of York, UK and EPFL, Switzerland.

Browse articles by content type

Ask me anything: Raghavendra Srinivas – ‘Experimental physics is never boring’

What skills do you use every day in your job?

What do you like best and least about your job?

What do you know today, that you wish you knew when you were starting out in your career?

Julia Sutcliffe: chief scientific adviser explains why policymaking must be underpinned by evidence

Eco-friendly graphene composite recovers gold from e-waste