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Danko van der Laan (promotion date: 30 January 2004)

Flux pinning and connecting in polycrystalline high-temperature superconductors

Promotion date: 30 January 2004

Danko van der Laan

The electrical loss in for instance high voltage cables is under normal circumstances about 10%. A lot of materials have superconductor properties when functioning at a low temperature, which makes a more efficient production and transport of electrical power possible. I investigated the possibilities for improvement of high-temperature superconductors for the use in power applications. The problem is that at this stage the high-temperature superconductors cannot be applied as yet because they are expensive and there are still problems to be solved.

What was your thesis about?

The electrical loss in for instance high voltage cables is under normal circumstances about 10%. A lot of materials have superconductor properties when functioning at a low temperature, which makes a more efficient production and transport of electrical power possible. I investigated the possibilities for improvement of high-temperature superconductors for the use in power applications. The problem is that at this stage the high-temperature superconductors cannot be applied as yet because they are expensive and there are still problems to be solved. The materials are fairly new and not enough is known about things like durability and reliability. The quality of a superconductor is determined by its ability to sustain a large supercurrent. The granularity of the superconductor is responsible for reduction of the critical current density. Also the high magnetic field influences the extent of dissipation.

What is flux pinning?

The motion of magnetic field lines under the influence of a Lorenz force also interferes with the performance of the superconductor. That is why you want to pin the flux lines, in order to prevent them from moving.

So your research was highly practical?

My research was in a large part practical, but is supported by theoretical studies as well. In several experiments investigated the mechanisms responsible for dissipation and modelled them theoretically. Only when you understand the mechanisms well you can improve the quality of the conductor and their manufacturing methods.

Had that never been done before?

Not in such a conclusive way. I actually determined and illustrated the exact causes of the loss.

I imagine that power companies are interested?

Yes, some people in our group actually collaborated with power companies on certain applications.

Did you do all the experiments here at this university?

I spent 2,5 years of my promotion research in Florida. I first did my training at the High Magnetic Field Lab in Tallahassee, where they build the largest magnets in the world, and they asked me to do a promotion. The University of Twente asked me to do a promotion as well, so I combined the two and spent half of the time here and the other half in the US. It worked out well. They were pleased to have me, you contribute a lot in the way of science.

How did you manage to keep close contacts with your supervisors here?

I went back at least once a year and did several experiments at this university. Before conferences and when something new came up we had frequent contacts by mail, so it wasn’t really a problem.

Did you like living in the US?

Yes, I enjoyed it, even to the extent that I am going there again. I got a job offer from Colorado for a two years’ postdoc again on superconductors.

Was the international experience important to you?

Yes, I enjoyed the time I spend in Florida, so I actively looked for a position in the US. As a graduate student in the US, you normally don’t have a restricted time frame in which you should finish your Ph.D. As a foreign student who has to finish within four years, you have to make sure that you spend your time efficiently. You have a lot of possibilities in the U.S., after finishing your Ph.D. I would say more than in the Netherlands. Even there budget for research in superconductivity is tight now, but still there are more ways to get your research funded.

For the summary of the thesis, click here.