I have been blogging a lot about nuclear fusion power systems research lately. If we could duplicate the process that fuels the stars themselves, it would solve a lot of problems here on Earth. Fuel should be cheap and plentiful, radioactive waste would be severely reduced or eliminated altogether, and costs and construction time would be reduced compared to commercial nuclear fission power plants.
The Joint European Torus (JET) is operated by the U.K. Atomic Energy Authority at the Culham Centre for Fusion Energy (CCFE) located near Oxford, England. Scientists from twenty-eight European countries have come together at the JET facility to research the potential for carbon-free fusion energy. The work is coordinated by the EUROfusion which manages and funds European fusion research activity for Euroatom. A series of tests are being conducted at JET which will provide important information at the ITER project in France. ITER is an experimental fusion reactor that is being constructed as a collaboration of several countries.
The JET is a tokamak fusion reactor design. An exhaust system called the “divertor” removes both the extreme heat generated in the torus and impure particles from the hot plasma fuel. One of the problems that has arisen in the effort to scale up the JET to a bigger system like ITER is that the components of the divertor on the ITER cannot take the high levels of exhaust heat because they will be damaged.
Representatives of CCFE said that one possible solution to the divertor is the deliberate use of an impurity such as nitrogen to cool the plasma by radiating the heat over a broader surface area in the diverter section. Unfortunately, nitrogen can form compounds at the high temperatures in the diverter which can include tritiated ammonia. This gas is not compatible with the processing systems in the JET.
An alternative to the use of nitrogen for cooling is the use of neon gas. However, the previous level of heat that can be generated by the JET has not been able to produce the same effects as nitrogen without impacting how well the plasma can be confined in the tokamak which is a key factor in assessing the performance of a fusion reactor. The researchers have overcome these problems by raising the heat in the tokamak and injecting additional neon into the plasma.
Carine Giroud, who coordinated the experiment, stated that the findings that neon could be used to radiate and improve the pedestal is very significant. He said "We had extra power from JET's neutral beam heating system which allowed us to put in more neon, and it was both these elements which led to the improvement. We haven't yet achieved our target for reducing power to the divertor tile at the outer strike point, but we have seen that the temperature of the divertor tile didn’t increase significantly during the time where the radiation from the neon was applied. This was something we could do with nitrogen in previous years but not with neon - but now we can."