Forty years of working on nuclear fusion research: what’s that like? How has fusion research changed over the years, looking at the progress that has been made and the technological developments that are taking off? Now that his retirement has come, it’s time for DIFFER’s former department head Egbert Westerhof to reflect on his career in fusion.
How did you end up in the world of nuclear fusion?
“I joined FOM Rijnhuizen as a PhD student in 1983 after studying plasma astrophysics at Utrecht University. At that point, I had no connection whatsoever with nuclear fusion. My plan was to continue as a PhD student in astrophysics, but there were four good students and only three positions. I then started looking for other interesting topics and came across a vacancy at FOM Rijnhuizen for plasma physics in the field of fusion. That way, I was still able to apply the knowledge of plasma physics I’d gained during my Master’s.”
What was your PhD research about?
“My research initially focused on heating plasma using Electron Cyclotron Resonance (ECR). The FOM Institute was just about to start one of the first experiments with Electron Cyclotron Resonance Heating (ECRH), which was unique in Europe. For this, three gyrotrons were installed by FOM at the Tokamak de Fontenay-aux-Roses (TFR), just outside Paris. Each had a pulse duration of 100 milliseconds and a maximum power of 200 kilowatts. That was state-of-the-art at the time. I also spent some time at JET (Joint European Torus) in the UK during that period, looking into sawtooth oscillations. I was keen to find out how to simulate them, something we now call integrated modelling. You could actually say that we were pioneers in that field.”
How did you continue your research work after completing your PhD?
“I completed my PhD in 1987. The gyrotrons we’d used in the four-year ECRH project were moved to FOM Rijnhuizen. After a few years, a new gyrotron arrived with a higher frequency and greater power, enabling us to study the heating process even more effectively. As ECRH remained an important topic within the lab and, as a newly qualified PhD graduate, I was one of the few with theoretical expertise in that field, I was offered a permanent position in the theory department. I then began researching the influence of ECRH on instabilities in the plasma.”
What challenges did you face as a fusion researcher at that time?
“In the late 1980s and early 1990s, the Rijnhuizen Tokamak Project (RTP) began at Rijnhuizen. The RTP tokamak was a relatively small tokamak with limitations. We then began collaborating with TEXTOR, a tokamak in Jülich, Germany, which was 1.5 times the size of RTP. The most powerful gyrotron at RTP was subsequently moved to TEXTOR. An even more powerful gyrotron (140 gigahertz, nearly 1 megawatt) was added there later. And there was a vague idea at the start that the Free-Electron Maser (FEM) from Rijhuizen could also be installed at TEXTOR. However, that never happened. With a FEM, you could build a high-power source that could be continuously tuned on a short timescale. If it had been a success and we’d been able to achieve that at TEXTOR, the world would have looked very different now.”
What can be seen as a highlight of the work at TEXTOR?
“At TEXTOR, they had the dynamic ergodic divertor. This divertor had the advantage of being able to generate, in a controlled manner, the very instabilities responsible for disruptions. We had a brilliant idea, namely: if you want to stabilise or suppress those magnetic islands using ECRH, you have to deposit the ECRH power precisely within that island. That’s precision work, and you need a feedback control system for it. My idea was to look through the pipe used to feed the megawatt power into the plasma. Then, by observing the emission, you can see exactly where you are within the plasma. So you take measurements via the same path through which you apply the heat. The project was called Inline ECE and it was one of the highlights of the work we did on TEXTOR.”
And then a pleasant surprise awaited you?
“With Inline ECE, we discovered a new phenomenon in the plasma as an unexpected bonus. Whilst locating the island in the plasma, we suddenly started receiving a lot of interference in our measurements. We discovered that the presence of the island causes a parametric decay instability in the waves you send in. This results in the scattered reflection of that radiation at lower frequencies. It had been predicted that this would occur, but only at much higher power levels. We discovered this by chance on TEXTOR, and it remains an active area of research to this day. During my symposium on 3 September, a Danish researcher will be giving a talk on the subject.”
What was your time at TEXTOR like?
“It was a wonderful time, both personally and professionally. During my time at TEXTOR, my wife and I lived near Jülich for ten years and our children were born there. At the start of that period, JET was also opened up for experiments, and I was involved in that as well. When my children were born, I traveled less, so I temporarily put those kinds of things on hold. From a scientific point of view, this was my most fruitful period. I was able to do a lot of interesting work there, including publishing extensively. The most important thing for me was the Inline ECE development, which resulted in one of the very first experiments to demonstrate genuine feedback control of magnetic islands. In 2008, I returned to the Netherlands where my focus was mainly on the modelling work.”
The way research is conducted has changed considerably over time, given all the technological developments. Could you tell us a bit about that?
“We did have computers in the 1980s and 1990s to carry out calculations, but they were, of course, different from today’s. The programmes were less advanced than they are now, and the theories weren’t as far developed as they are today. We had to run our calculations on the computers in Amsterdam. Down in the cellar of Rijnhuizen Castle, there were terminals that allowed us to connect to those computers. Fortunately, I didn’t have to cycle to the computer centre with stacks of cards!”
What were memorable moments for you in nuclear fusion research?
“The TEXTOR era definitely was. Discovering the effects with Inline ECE, getting the Inline ECE diagnostics up and running in the first place, and establishing feedback control of magnetic islands. As far as I’m concerned, those are the internal highlights. If you compare that with international research, then of course there was the launch of JET in the early 1980s. At one point, JET was upgraded to include a divertor, and that’s when the first DT experiments took place at JET. Yes, those were certainly important moments in fusion research. But of course, the launch of the ITER project was too.”
What major challenges are nuclear fusion researchers currently facing?
“It’s a very interesting time again. You’re seeing all these private initiatives taking off. And the realisation that we’re now very close to achieving nuclear fusion. It’s really a perfect time to be actively involved in fusion research now. You can expect considerable progress over the next 5 to 10 years. Think of the results we’ll be seeing from SPARC (Commonwealth Fusion Systems). A little later, the results from Proxima Fusion’s Alpha stellarator will follow. Then BEST in China will also bring its DT experiments online. And within 10 years, ITER will have started its experiments too.”
Those are truly major milestones in the field of nuclear fusion, aren’t they?
“Yes, and they make the coming decade an incredibly crucial one. After all, we’re not yet certain whether it will all work out or not. It’s experimental, and we’ll have to see whether, once they switch on a tokamak at some point, everything works as it should.”
You were head of the fusion department at DIFFER for six years. What type of leader were you?
“I approached it very much as a form of servant leadership. In doing so, I tried to create the conditions in which team leaders could get the best out of their teams and their work. I also felt it was important that we kept the collective interest in mind.”
How will you remain involved in nuclear fusion research after your retirement?
“I’ll be able to remain active for a while longer. I’m a member of EUROfusion’s E-TASC Scientific Board until the end of 2027. If there are other ways I can make a useful contribution at DIFFER, I’ll be more than happy to continue doing so.”
What advice would you give to the next generation of researchers?
“The focus is shifting more towards technology and less towards getting to the very bottom of the details of physics. There is also lots of fundamental work to be done on the technological side. I would also say: it’s not just about plasma physics, there’s more. The focus is shifting more towards all the peripheral systems of the tokamak. And towards what happens to the materials. The field of research is incredibly broad and multidisciplinary, and the international collaboration that has always existed has become increasingly close over the years. That collaboration remains crucial.”
On 3 September 2026, DIFFER organises a farewell symposium on the occasion of the retirement of Egbert Westerhof: ‘The future of electron cyclotron waves’. We invite you to join us in celebrating Egbert's accomplishments in fusion research and exploring the challenges and opportunities that lie ahead. Visit the website for more information and to register.
Author: Rianne van Hoek
Translation using DeepL
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