Professor Xavier Garbet, the Temasek Chair in Clean Energy at NTU’s School of Physical and Mathematical Sciences.
In his cool, air-conditioned office at Nanyang Technological University (NTU), Singapore, Professor Xavier Garbet is thinking about some of the hottest matter in the universe.
Professor Garbet, the recently-installed Temasek Chair in Clean Energy at NTU’s School of Physical and Mathematical Sciences (SPMS), is an expert on plasma physics. His research aims to understand turbulence in hot plasmas, a topic that is critical for designing nuclear fusion reactors. One day, such reactors could be a source of abundant and sustainable energy for humanity.
In nuclear fusion, two or more lighter atomic nuclei combine, or “fuse”, into a heavier one. Tremendous amounts of energy are released in the process, which powers stars like our Sun. Unlike nuclear fission (the splitting of heavier nuclei into lighter ones), nuclear fusion does not directly produce any long-lived radioactive elements. This and other advantages have inspired generations of physicists and engineers to find a way to use nuclear fusion for energy generation.
And yet, the dream of creating a nuclear fusion plant has remained unfulfilled for over eighty years.
Nuclear fusion occurs in a hot plasma: a fluid of fast-moving atomic nuclei, usually trapped by strong magnetic fields. In some reactor designs, the temperature of the plasma is required to be over a hundred million degrees Celsius, hotter than the core of the Sun. Unfortunately, such a fluid is prone to turbulent motion, like the chaotic swirl of air in a car driven with the windows down. This unpredictable motion makes the plasma incredibly difficult to confine to the center of a reactor. And if it escapes, its high temperature can damage or even destroy the rest of the reactor.
To tame the turbulence problem and open the way to working nuclear fusion reactors, Professor Garbet is using a variety of methods to better understand how hot plasmas flow: theoretical modeling, computer simulations, and machine learning. His research is part of a crescendo of global efforts that have recently raised fresh hopes for nuclear fusion technology. At NTU, Professor Garbet hopes to tap into Singapore’s technological know-how and skilled manpower, in preparation for a possible clean energy future with nuclear fusion.
We recently sat down with Professor Garbet to learn about his research.
Please tell us a little more about your current role as the Temasek Chair in Clean Energy.
Prof. Garbet: My activities as Temasek Chair in Clean Energy are multi-faceted. The overall aim is to prepare for when technology matures enough to build a commercially viable fusion reactor. I am coordinating a range of research activities that leverage on the strong expertise in NTU, namely mathematics, physics, computer science and experimentation.
One priority is to develop computer models suitable for designing a reactor. There has been a lot of progress in this, thanks to improvements in ab initio simulation methods, and the arrival of artificial intelligence techniques.
A second objective is to develop devices that can characterise the properties of a fusion plasma, at temperatures as hot as 100 million degrees.
A third objective is to train students and research staff, to build up skills in this topic in Singapore. As part of this, I started teaching a course about plasma physics for fusion clean energy in August 2023.
This research and education programme is jointly funded by the investment firm Temasek, Singapore’s National Research Foundation, and NTU. Discussions are also ongoing with A*STAR, and also private companies to extend this course of action.
Last but not least, I am in the process of establishing a joint research laboratory with CEA, the French agency for atomic and alternative energies in France. A master research collaboration agreement (MRCA) was signed between CEA and NTU on 23 October 2023.
What got you first interested in this area of research?
Prof Garbet: I was attracted by the prospect of developing a clean and safe source of energy. Fusion is a source of energy that offers many advantages.
First, the fuel makes use of deuterium and lithium, elements that are abundant on Earth.
Second, a reactor produces little radioactive waste, with a lifetime of around a hundred years, not hundreds of thousands of years like with fission reactors.
Third, it is very safe, since a burning plasma is easy to stop. Unlike in a fission reactor, no chain reaction is possible.
But to get to a working fusion reactor, there are many interesting challenges to address. Fusion in a terrestrial reactor requires very high temperatures, over a hundred million degrees Celsius in some designs. At the same time, the fusion energy needs to be delivered to electrical turbines, which must be at a much lower temperature, several hundreds or thousands of Celsius. These two requirements – a very hot reactor core, and a strong temperature gradient between inside and outside the core – set up the conditions for turbulence in the plasma. Controlling these turbulent flows is a major ongoing research problem.
Fusion research is fascinating because it is at the forefront of a wide spectrum of challenges in modern science and technology. It has connections with other enthralling fields of research like astrophysics, hydrodynamics, and geophysical fluid dynamics.
What do you hope your research will lead to in the future?
Prof Garbet: I hope that my research will lead one day to a reliable fusion reactor that produces clean energy at an affordable cost. I also wish that some of the basic research in maths, physics and computer sciences will be useful to other fields.
What questions pertaining to your work are deeply interesting to you right now?
Prof Garbet: The short answer is many! One issue is to improve the stability of a plasma. In that regard, the gamma ray spectrometer we are presently developing in NTU, and that will be implemented on the WEST fusion device in France, should improve our knowledge of a fusion plasma.
Another challenge is how to enhance the confinement of a plasma with a 100 million degrees temperature. This is done by playing with the intense magnetic field that guides the particles in the plasma. I hope that the modelling tools we are currently developing in NTU will help to improve both stability and confinement capabilities of a fusion plasma.
What excites you most about the work that you do?
Prof Garbet: My favourite activity is to understand observations via theory and modelling, then devise strategies to improve the quality of a fusion plasma. A nice aspect of this work is that I get to interact with a variety of scientists with different forms of expertise, and different points of views.
The path from an idea to its materialisation usually takes some time. Success is thus quite rewarding!
What has been the proudest moment of your career so far?
Prof Garbet: Devising a strategy that proves successful during experimentation is something that makes me proud – this does not occur that often though. Developing a model able to reproduce an observation is quite easy. Predicting what will occur in an experiment is much more rewarding.
One achievement I am quite proud of is the elaboration of mechanisms to increase the density in a fusion plasma. Fusion power increases like the square of the density. Theory came first, and proved correct after experiments on the Tore Supra tokamak.
Another achievement was to predict that turbulence can spread from one part of the plasma to another (an unfavourable effect, unfortunately). This was demonstrated recently in Japan, Korea and China, nearly 30 years after my first paper on the topic.
Could you tell us about any challenges that you faced during your career and how you overcame it?
Prof Garbet: Challenges in fusion science often come from physical or technology limits. Also information is often missing due to a simple lack of measurements: a plasma with a temperature of 100 million degrees is not easy to probe!
Solutions have usually come by confronting sparse experimental data with intensive modeling. Many times, improvement came after a breakthrough in technology. For instance, modeling has benefited greatly from improvements in high performance computing. The amount of computing time my colleagues and I have been using, each year, has increased by a factor of 1000 during the past two decades.
What advice do you have for aspiring scientists?
Prof Garbet: Good science is led by observation, but observation may be useless without a theoretical framework. This is certainly true in fusion sciences, but I believe is also true in many other fields or research.
So, my advice is to combine as much as possible: measurements, theory and modeling.
My second piece of advice is to broaden your scope. Very often, inspiration comes from other fields of research – pluridisciplinarity is always a plus.