When are we going to use fusion as a source of energy?

I remember 50 years ago they were talking about it, and so far I have not seen any of the present nuclear reactors replaced by fusion reactors. What is the problem?

The problem was the unrealistic expectations regarding our abilities to control the extreme temperatures in which fusion can burn (hundreds of millions of degrees Celsius). As it turns out it was easier to create the high temperatures than it was to control the plasma we had created. However we have now developed sophisticated magnetic field control and feedback mechanisms which allow us to control the plasma, at the temperatures required for fusion.

Up to now there has been a steady progress towards the target parameters of heat, density and confinement time. In 1997 JET demonstrated a significant release of fusion power, 16 megawatts, which was about 65% of the external heating input. Today, by extrapolating the “evolution not revolution” fusion experience, we are confident that the next step device, ITER, will actually produce controlled releases of fusion energy.

As a consequence, a lot of consideration is now devoted to the technological challenges of fusion, such as the selection of materials that will face the heat of burning plasmas. These details have been hardly ever considered before. ITER has finally received large political support on a global scale, and will be built within ten years. After a few years of tuning experiments, we expect to see the first burning plasmas by 2025.

However, these projects are such large undertakings that even if everything works perfectly, it will take some years simply to build the technology. Allowing time for fine tuning about 20 more years will be needed to transfer the technology from research to industry.