Door: CN Rood DIFFER, the Dutch Institute for Fundamental Energy Research, is an institute specialised in fusion energy and solar fuels research. DIFFER's research is of great value for the nuclear fusion reactor ITER. This technology should provide our energy in the future. Wim Melissen is responsible for the particle accelerator at DIFFER as Ion Beam Technician / Operator. We spoke to Wim about ITER, the role of DIFFER in this project and about the collaboration with CN Rood. By using Delta power supplies (supplied by CN Rood), new measurements can now be performed that were previously impossible.
Nuclear fusion reactor ITER
In Cadarache (southern France), an advanced pilot version of a nuclear fusion reactor, ITER (International Thermonuclear Experimental Reactor), is currently under construction. This is intended to be the first nuclear fusion reactor to generate more energy than is needed to heat and control the fusion plasma. The advantage of generating energy with nuclear fusion is that such a plant does not emit CO2, uses widely available raw materials, and the fusion process is safe and does not produce radioactive products. In the fusion reactor, deuterium and tritium are heated to extremely high temperatures. (around 150 million degrees Celsius). To prevent the hot plasma from hitting the relatively cold wall of the nuclear fusion reactor and thus losing its heat, magnetic confinement is used. Moreover, you also have to make sure that the apparatus in which you make this hot plasma can withstand these high temperatures.
Tungsten wall
The particles that manage to escape despite the magnetic confinement cause the wall to take quite a beating. These particles bombard the wall with as many as 1024 particle impacts per square meter per second. When choosing the wall material, the least sensitive to this was considered. The wall also had to withstand heat of more than 10 MW per square meter. You can compare this to conditions in a welding flame or on the surface of the sun. Tungsten was chosen for the ITER project because this material has a very high melting point (3500 degrees Celsius), good thermal conductivity and a high mass number. The latter ensures that the relatively light particles created in nuclear fusion do not easily detach tungsten atoms from the lattice.
DIFFER examines wall of tungsten
At DIFFER, an Upgraded Pilot-PSI (UPP) particle accelerator is used to test the Tungsten. Wim Melissen: "The Upgraded Pilot-PSI (UPP) is a new test facility within DIFFER used to generate high-flux magnetised linear plasma and that makes it possible to simulate ITER conditions. This new setup also allow us to monitor everything in real time. In the past, test data was stored and read out and analyzed later. What we want to measure is whether the surface of the tungsten test component has deteriorated. What you don't want is for the properties of the tungsten wall to change and for the ITER reactor to have to be shut down in the future."
Delta power supplies crucial for measurements
The plasma in the linear plasma generator is generated by a DC cascaded arc, and magnetised by 3 sets of copper coils. Wim Melissen: "We used three power supplies altogether 400A, the problem with these power supplies was a ripple of 4A at 40KHz. This ripple disturbed the measurements and made the results useless. Tests were scheduled but we came to the conclusion that with these power supplies, the tests could not go ahead. We then contacted CN Rood. CN Rood had Delta power supplies (SM70-CP-450) in stock and we hired them for the test. This was arranged within a few days and the tests could go ahead. The results were so good (a ripple of 0.1A at 300KHz) and the interference, which is 40x lower, could be completely filtered out. We are now able to make measurements that we could not do before. We like the Delta power supplies so much that we bought them immediately. We are very satisfied with the power supplies and CN Rood's fast service!"
For more information contact CN Rood or DIFFER!
