New methods takes temperature of fusion reactor

23 October 2008

For fusion energy to be commercially viable, better methods are needed for metering the temperature and output in a fusion reactor. In his doctoral dissertation, Henrik Sjöstrand demostrates a new method for this. He is publicly defending his thesis on October 24 at Uppsala University.

Two of the most important parameters in a fusion reactor are the combustion intensity, which controls how much energy the reactor produces, and the temperature of the fuel. Better and more precise knowledge of these is needed if fusion energy is to be able to take the step from vision to reality.

“In a car engine the output is determined by the pressure and the temperature,” explains Henrik Sjöstrand of the Department of Physics and Astronomy at Uppsala University. The same is true for a fusion power station. In order to understand the combustion process, we need to be able to measure pressure, temperature, and output.

In his thesis Henrik Sjöstrand presents an improved method for metering the extremely high temperatures and reaction speeds in the fusion plasma.

The fuel needs to reach several hundred million degrees to “kindle,” which makes it extremely difficult to deal with.

“We can’t just put a regular thermometer in the fuel.  It would obviously be destroyed and pollute the fuel.  In other words, we have to measure the properties of the fuel remotely.”

One way of doing so is to study the electrically uncharged neutrons that come out of fusion reactors. They carry with them important information about the combustion process.

A prototype instrument was installed on the European experimental reactor JET, Joint European Torus, in 1996. This instrument studies neutrons from deuterium-tritium reactions. Working with colleagues, Henrik Sjöstrand has upgraded the instrument for use in deuterium experiments, which are more common.

“Future fusion reactors will run on deuterium and tritium.  But deuterium is cheaper than tritium, and, unlike tritium, it’s not radioactive.  Therefore we want to run as many experiments as possible on deuterium alone.  This means that experiments with only deuterium are simpler to carry out and can provide information about a lot of the physics taking place in a reactor.”

Henrik Sjöstrand has also developed a method to determine the total neutron production and thereby the fusion output and the consistency of the fuel.

“It’s absolutely essential to the operation of a fusion power station.  With the new instrument we can also see how the fuel is heating up.  For example, we can measure how efficient the microwave heating process has been.”

For more information, please contact Henrik Sjöstrand at cell phone: +46 (0)733-13 04 66 or