Inertial Confinement Fusion and the Breakthrough in Fusion

On December 13th, 2022, the Lawrence Livermore National Laboratory, the home of the National Ignition Facility, announced that they have achieved a net power gain from fusion, where the energy released from the fusion event is greater than the energy focused onto the hohlraum (an ampule containing nuclear fuel) from the lasers.

In reality, whilst this proved that net power gain from fusion is possible, this is nowhere near feasible nuclear fusion power generation that these articles seem to herald, and this breakthrough should not be reframed to strengthen the idea that commercial fusion power is only two or three years away as some promising startups might promote. 

A macroscopic effect is the heating of the plasma, and the outward expansion of the plasma. The main challenge is to control this outward expansion so that nothing valuable is damaged, or the plasma’s expansion is channelled in such a way that it can be controlled.

The technology demonstrated to achieve ignition, is inertial confinement fusion. As the name suggests, it relies on providing so much compressing force on the plasma very quickly, that the sample heats up and undergoes fusion under these extreme conditions, and the inertia of the plasma itself maintains conditions suitable for nuclear fusion, and prevents the plasma from expanding back out and dissipating away too quickly. This limits the maximum length a fusion plasma can be sustained as to a brief pulse of fusion. Whilst this makes researching the properties of fusion-sustaining plasma easy, ICF is difficult to scale up, as the whole chamber has to be cooled down, fuel wastes dumped out, and another fuel capsule inserted, before the next fusion reaction can begin, which is a lengthy process. Currently, NIF fires at a rate of once a day. In order to generate energy at a cost effective rate, a similar system would need to fire several times a second, which is completely impossible with our current technology, due to the complexity of every component involved in the process. As a result, the main focus of research is on the development of magnetic confinement fusion technology, where the plasma is confined, suspended, and compressed using strong currents and powerful magnetic fields. This allows the plasma to be sustained for much longer, and does not require a lengthy reloading process which is required by current ICF implementations. 

And we should not be so surprised that fusion with Q > 1 is achievable. We have demonstrated this time and time again -- nuclear weapons. (almost) All current nuclear weapons rely on a secondary, fusion stage, where a small conventional fission bomb (the primary stage) detonates, generating x-rays which compress and heat up the secondary stage (the hydrogen tanks) to fusion conditions. The resultant fusion of the hydrogen generates the bulk of the explosive power of the nuclear device, therefore technically giving every nuclear weapon ever, a Q value of much greater than 1. But just like with the National Ignition Facility’s breakthrough, we have not yet managed to find a way to extract power in a useful way out of such a system, or convert such technology into a continuous power source. All our hope still rests on tokamak development, and in the grand scheme of things, the NIF breakthrough is just another small step on a multi-decade long hike.