P.H.D. Student Interviews - Part 10

"I am fascinated by superconductors and nuclear fusion is a great application field for that in the form of magnets"

Sigrid Holleis, doctoral candidate at the Vienna University of Technology

What is the topic of your Ph.D. thesis? 

I work in the field of superconductivity and for my dissertation I focused on thallium-based high temperature superconductors.

What is the focus of your research?

The high temperature superconductor thallium-bismuth-barium-strontium-calcium-copper-oxide or short TI-1223, has been known for some years, but its potential has never been fully exploited. Other copper-oxides, like the REBCO or BSCCO compounds, are well-known and developed, but they show certain weaknesses when it comes to applications. With the use of thallium-based superconductors, we want to enable higher currents at higher temperatures and in addition a cheap and simple production process.

In the framework of this project, I study the superconducting properties of Tl-1223 thin films. With Hall Probe Microscopy we can investigate the critical current in the superconducting grains and across grain boundaries. Furthermore, I compare the obtained results with the microstructure of the superconductor, in order to determine the reasons for good or bad current flow in different parts of the sample.

What is the benefit for fusion research?

For nuclear fusion with magnetic confinement, like at the ITER fusion device, which is currently being built in Saint-Paul-lez-Durance, France, very high magnetic fields are essential. The corresponding magnet coils consist of superconductors, whose production process is very expensive and demanding. The currently used superconductors can only operate at very low temperatures, which makes cooling with expensive liquid helium necessary.

For the commercial usage of fusion reactors, it is important to develop a superconductor, which is cheap and easy to produce. With a superconducting wire based on thallium it could be possible to achieve higher conductor performances which could make the magnet design more compact and in addition cooling with much cheaper liquid nitrogen would be possible.

What are the biggest challenges?

Of course, with such a large project, we have to work together with other institutes here and abroad. That is exciting, because you can get inputs from many different sides, but it is not always easy. You see your colleagues only once or twice a year at project meetings, while further communication takes place via email and video chat. For instance, the samples I study are not produced in our home lab. Therefore, waiting periods can occur, which can be used for discussions about the results, but no new measurements can be done.

Which plans do you have for your future? What will you do in 5 years? Would you like to continue research or are you going to work in industry?

In no case I would like to determine right now in which direction my further career path should go. According to my previous experience, our international network offers great opportunities to stay in the research field, but on the other hand, I can also imagine working in the private sector. I like new challenges and my future job should be at least as exciting and diversified as the work on my dissertation.

What was your motivation to write a fusion relevant Ph.D. thesis? What is fascinating about nuclear fusion?

Let’s say it like this: I am fascinated by superconductors, because they enable loss-free energy transport over very large distances. What is so exciting about nuclear fusion is that it is a great application field for superconductors in the form of magnets. We could have environmentally friendly energy production and transport in one go, and that I can make a small contribution to such a future with my work is already a nice thought.