Originally published in "Physics of Plasma", the Max Planck Society has briefly and concisely summarized the current status of various nuclear fusion systems. Certainly the most interesting in this context is the so-called triple product, which represents the density of the available atomic nuclei, their temperature and the duration of a stable state as a multiplication of these values.

If the result is high enough, the threshold for a positive energy balance is exceeded by the respective technology. This means that more energy comes out than was put in. This is exactly what was achieved for the first time with laser fusion in 2021. The US research facility "National Ignition Facility" fired laser light at metal spheres.

The X-rays triggered in this way heat the hydrogen inside to the required temperature. At the same time, the pressure in the closed system increases considerably, which accelerates nuclear fusion. Ultimately, the thermal energy exceeds the required laser energy.

In a further step, the sphere can also be fired at directly until it implodes, but without additional X-rays. However, this does not yet work very reliably. And unfortunately, a new sphere has to be inserted every time. Continuous operation, which would be necessary for a power plant, cannot be realized with this method.

Energy balance meets reality

In theory, however, a tokamak - a gigantic electromagnet with plasma circulating inside, which is heated to temperature by means of external radiation and internal heating - is capable of precisely this continuous operation. However, the energy requirement is so enormous that not even ITER, the first fully functional nuclear fusion reactor still under construction, could generate electricity - on the contrary.

However, the technology is mature, has been researched for decades and is suitable for a commercial power plant if the energy surplus is ever reached. This does not mean that another concept cannot still overtake the tried and tested ideas. For example, there are plans to generate additional pressure in a tokamak. This would significantly reduce the required temperature, meaning that this principle is at least within sight of feasibility. The triple product corresponds to that of the JT-60U tokamak in Naka, Japan. This means, that ten times more energy is required than can be produced.

Other ideas aim to use impact energy to cause a sudden increase in pressure and temperature. "First Light Fusion", a spin-off from Oxford University, is firing a capsule filled with hydrogen. The shock waves triggered are intended to generate the necessary pressure to create better conditions for nuclear fusion. However, only the basic idea is clear here, the implementation remains nebulous.

And at the TAE and Helion companies, two packets that have already been converted into plasma are shot into a magnetic field at maximum speed and collide directly with each other. However, until now you have to put a thousand times more energy into this system than you get back.

Conditions like those in the core of the sun: there are many ideas and research will continue, as the still distant goal is far too tempting.