What is the latest story on nuclear fusion? – A look behind the latest noise in the press

In recent months, we have been hearing a lot of news from the press on a topic that has been characterized by a long silence for decades. For example, on one and the same day (January 26, 2022), almost all press organs carried headlines such as:

• ‘Burning’ hydrogen plasma in the world’s largest laser sets fusion records
• Nuclear fusion milestone creates „burning plasma“ for the first time
• Physicists create self-burning plasma -but is it a step toward sustainable nuclear fusion energy?
• Scientists reach major milestone in harnessing fusion energy

Progress in nuclear fusion (as opposed to nuclear fission, on which today’s controversial nuclear power generation is based) is of great importance, because nuclear fusion offers the possibility of safe and (almost) climate-neutral energy generation.

Yet the history of nuclear fusion research is already more than 80 years old. Since the 1930s, physicists have known that hydrogen nuclei fuse to form helium atomic nuclei under very high pressure and temperature – and that it is this mechanism (as well as the fusion of larger atomic nuclei) that enables the sun to generate its enormous amounts of energy. The amounts of energy released in this process are far greater than in the reverse process, in which heavy atomic nuclei are split, which has been used in nuclear power plants for more than 60 years. The reason for the energy gain is that a small amount of mass is lost during the fusion of light atomic nuclei. This mass defect manifests itself directly in the (kinetic) energy of the particles produced. According to Einstein’s famous formula E=mc², this energy is enormous even for the small amount of mass lost: This is because this mass (m) is multiplied by the square of the speed of light (c²). Thus, the basic concept of nuclear fusion worked out at that time is still the same today: A deuterium-tritium plasma (deuterium and tritium are isotopes of hydrogen, i.e., a proton together with one and two neutrons, respectively) is heated to several million degrees in a kind of microwave and then confined and controlled with the aid of a magnetic field (such a plasma consists of charged particles and can therefore be controlled by magnetic fields). At a temperature of about 100 million degrees, the mixture ignites and releases the fusion energy (although the specific ignition temperature depends on the particle density, i.e. pressure of the plasma).

Recent headlines have specifically focused on the achievement of scientists at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory in Northern California. Here, a high-power laser was used to create for the first time a „burning plasma“, demonstrating for a (very) brief moment how the „fuel“, i.e. the combination of deuterium and tritium, can be made to undergo nuclear fusion and thus produce energy. The energy achieved here was much of the energy required to sustain the nuclear reaction. This corresponds to the reactions in the interior of the sun, whereby here on earth the problem is that for the production of these reactions enormously high energy quantities or densities are necessary at first, in order to set the process in motion, which then maintains itself (on suns of a certain size this is caused automatically by the enormously high gravitational force).

The results of experiments conducted by NIF in November 2020 and February 2021, and then in August 2021, and now communicated, describe important steps toward this goal using high-energy lasers that generate the energies needed in a very small space for this reaction to occur within. But this is only one of many possible methods. Different experimenters propose different methods to potentially sustain the fusion reaction at high temperatures and pressures. NIF specializes in an approach called „inertial confinement,“ where high temperatures (in very small spaces) are generated by bombarding a tiny hydrogen bead at the center with 192 high-power lasers. Specifically, this is to be achieved by carefully shaping both the fuel capsule – a tiny spherical shell of polycarbonate diamond that encloses the pellet – and the cavity containing the pellet – a small cylinder of depleted, or not very radioactive, uranium lined with gold. This should reduce the fuel to a minimal fraction of its volume within 10 billionths of a second, allowing its core to reach a temperature of 50 million degrees Celsius, sufficient for nuclear fusion under the correspondingly high pressure conditions. However, the lasers themselves consume enormous amounts of energy and so far can only be ignited once or twice a day. So there is still a long way to go before this process can be realized in practice. But in the August experiment, as for a very short time almost as much energy was extracted from the fuel pellet as was put into it, researchers now expect that future experiments will soon be more powerful (though still for only a very short time). But still, by most nuclear physicists, the laser method is unlikely to be a path to commercial reactors because of the short duration of the process. And it should not be forgotten: NIF’s main focus is not on clean energy production, but on U.S. military interests („national security“).

Just a few months earlier, incidentally, there had been a similar wave of newspaper articles on nuclear fusion. The trigger here was the Boston-based company Commonwealth Fusion Systems (CFS), a spin-off of MIT, which received more than a billion dollars from investors such as Bill Gates and George Soros, as it communicated. The way this nuclear fusion works is quite different from NIF’s: here, it is more of a traditional fusion approach, building a donut-shaped „tokamak“ reactor, a „big magnetic bottle“, according to CFS’s CEO Bob Mumgaard, in which powerful magnetic fields control spheres in plasma that’s about 100 million degrees hot, which should produce the same fusion of hydrogen isotope nuclei as in the laser-driven reactor. Mumgaard said they will have a working reactor in six years basing his optimism on CFS’s successful 2021 summer test of new electromagnets made with barium-copper-oxide superconductors.

However, there will almost certainly be room for more than one fusion winner. Other companies include Canada-based General Fusion, backed by Jeff Bezos, which received $130 million from investors in 2021. And then there is TAE Energy in California, which is arguably the furthest along with commercially successful nuclear fusion, having already experimented with it at a cost of $1 billion over the past twenty years and now, with having successfully raised more money, plans to build the first permanently operational nuclear fusion reactor within the next three years, which they are already calling „Copernicus“. Initially, it is also to be operated with hydrogen isotopes and achieve a net energy gain around the year 2025. But then, because of its even better environmental and cost profile, the scientists at the company want to switch to p-¹¹B (proton-boron 11) fuel, because this reaction has the advantage of being „aneutronic,“ meaning that it does not produce the difficult-to-control high-energy neutrons that carry most of the energy generated by the fusion. Furthermore, it does not require the difficult-to-obtain heavy hydrogen isotope tritium. TAE plans to begin construction of Copernicus, a reactor that is an interesting combination of a particle accelerator and an ordinary plasma vessel, in 2022. The ultra-high temperature in the plasma is achieved by accelerating beams of fuel particles and letting them collide with plasma particles, something particle physicists have been doing for decades. The typical magnetically confined plasma donuts are replaced by an elongated plasma tube shaped like a hollow cigar. To improve stability, this tube is rotated around itself in such a way that the gyroscopic effect makes it much more stable. Theoretically, this approach can be used to get to much higher temperatures than the magic 100 million degrees. TAE has found evidence that the induced stability and quiescence in the plasma actually increases with higher temperature! It is precisely the hypothesis that this beneficial scaling property is maintained up to 3 billion degrees on which TAE’s approach is based. Here we will very likely learn a lot more in the near future.

The fact that investors are now willing to put up several billion dollars of private capital for the next round of funding for the development of nuclear fusion energy machines (with a correspondingly high expected return) shows that they expect to see commercially viable nuclear fusion in five or only a little more years. Otherwise, they would hardly put so much money into it. Commercially available fusion technology, if it were actually available to us one day – and perhaps soon – would mean a paradigm shift in society. If we were actually able to produce energy like the sun and thus gain access to the most efficient, safest and environmentally friendly form of energy that nature has to offer, this would certainly not only be another major technological advance, but rather a leap forward in civilization that would be on a par with the invention of the steam engine, which 250 years ago gave us the energy to completely turn our society upside down.