by Tim Fray
Following the interest in my post regarding the recent breakthroughs in reaching a viable fusion reactor at the Joint European Torus (JET) near Oxford, I thought I would add some more detail to put the achievements in perspective.
Although the problem still remains that the amount of energy put in is less than the amount of energy generated, the difference is getting smaller. The recent experiments at JET have shown this, and as such have provided hope for the larger ITER fusion-reactor project in France which the JET reactor is a precursor for.
ITER (“the way” in Latin), is boasted on the ITER website to be “the first fusion device to produce net energy. ITER will be the first fusion device to maintain fusion for long periods of time. And ITER will be the first fusion device to test the integrated technologies, materials, and physics regimes necessary for the commercial production of fusion-based electricity.” That’s quite a claim I think, even with the recent results, but as Daniel Thomas, former director of the European Patent Office quoted on my initial post on this subject “Hope Dies Last”.
What is important is that the recent JET experiments produced results over a period of five seconds. This doesn’t sound much but it is impressive compared to the 4 billionths of a second that it took for similar tests at the US Department of Energy’s National Ignition Facility’s fusion reactor. The US guys are doing it slightly different by bombarding the core with lasers, but they are hoping for the same effect. Indeed the US efforts have the record presently and have achieved an energy output of 70% of the energy input. Of course what we are looking for is something greater than 100% – the holy grail, but the scientists at JET believe that “if engineers applied the same conditions and physics approach to ITER as to JET, it would probably reach its goal of producing ten times the energy put in.” (Nature Nature 602, 371 (2022).
One issue that still remains however is how to convert the reaction products into usable energy, for example how to convert the kinetic energy and neutrons produced into electricity. Presently the energy is captured by heating a fluid. The Neutrons are fast-moving and electrically neutral so they are unaffected by the device used to contain the reaction. A layer of lithium surrounds the reactor core, which heats up when struck by a high-energy neutrons. Fluid such as water is passed over this layer and the water heats up to drive a turbine to generate electricity. Other methods blanket the core in nuclear fission material and the generation of heat is the same as in a convention fission reactor. And other systems could potentially derive power from the movement of charged particles within the system.
At the moment it would seem that the number of energy conversion steps is very large, and as we all know, every time energy is converted some is lost somewhere. But I am no nuclear physicist. And as for using steam power, something that was fashionable in the 1700’s , I would like to think we have moved on somewhat from there…or have we?