On a previous post, we commented about the recent record achieved by the Joint European Torus (JET), in a unique set of D-T experiments. In this post, we would like to add several other records set by other fusion devices. In particular, we will be talking about the Korea Superconducting Tokamak Advanced Research (KSTAR), the Experimental Advanced Superconducting Tokamak (EAST) and the National Ignition Facility (NIF). By all means, we can say that the period from 2020 up to the near future, will be remembered as a period of success and milestone fulfillment in the fusion field.
A distinction should be made between KSTAR, EAST and NIF as the physical mechanism to reach nuclear fusion is different. While KSTAR and EAST are two superconducting tokamaks, i.e. they rely on superconducting magnets which constraint the plasma shape and dynamics, NIF is a fusion device consisting of several lasers which heat and compress a small amount of a hydrogen (or an isotope as deuterium) pellet. Both mechanisms are known in the fusion field as, magnetic confinement fusion and intertial confinement fusion, respectively. Let’s now have a look at their respective records.
It should be noted that the International Thermonuclear Experimental Reactor (ITER), which will demonstrate the commercial feasibility of fusion as an energy source, is being developed according to the milestones reached by other tokamak devices, such as mentioned for JET in our previous post. Recall that we mentioned that JET had no superconducting magnets and, therefore, to avoid overheating the machine, one had to stop the plasma discharge after roughly 5 seconds. Of course, this time span is long enough to study the physics underlying plasma behaviour but it is not enough for a viable commercial fusion reactor which needs to deliver energy to the grid in a continuous way.
This is where the superconducting magnets come into play as well as the relevance of the KSTAR and EAST achievements. Both tokamaks possess superconducting magnets which allow for longer discharges to take place as long as the plasma is properly confined at a tremendous temperature, i.e. without damaging the plasma-wall facing components and avoiding instabilities to lead to a disruption. This is really not a trivial task. However, in December 2020 KSTAR set a new world record after successfully maintaining a plasma temperature of 100 million degrees (Celsius) for 20 seconds. It was really a success, and only one year after, in December 2021, EAST set a new world record after running the plasma for 1056 seconds (roughly 17 minutes) at around 100 million degrees (Celsius). These unprecedented results give a lot of confidence in the future capability of ITER to reach its goal, sustain the plasma for 10 minutes while delivering 500 MW of power.
While KSTAR and EAST use the magnetic confinement of hot fusion fuel, NIF approaches fusion using lasers that exchange linear momentum with the hydrogen atoms in the pellet, effectively compressing them. As the pellet gets compressed it also gets heated, to a point where fusion reactions start to occur. The idea is that part of the energy of these fusion reactions is able to maintain further fusion reactions, when this state is achieved, we say that ignition has been reached. This is exactly what NIF record is about, the experiment set a record with a release of 1.3 megajoules of energy during 100 trillionths of a second. This is a huge amount of energy coming from a fuel pellet which is only about 1 millimeter across.
What the fusion community and the society in general need to grab from all these successes is that work is being carried out and, more importantly, that we are advancing towards a joint goal, a long promised source of energy which looks now closer than ever. The fusion community strives on making the world a better place to live in.