Pathways to a nuclear fusion power plant
How close are current nuclear fusion experiments to an economical reactor with a positive energy balance?
Nuclear fusion occurs when the nuclei of lighter atoms, usually hydrogen, fuse to form heavier ones such as helium, releasing energy in the process. Fusion powers the Sun, but on Earth, the process can only be simulated in plasma at temperatures exceeding a hundred million degrees. No material can withstand such heat. As a result, research facilities and companies are exploring a variety of concepts for controlling plasma. The Max Planck Institute for Plasma Physics, for example, is researching the tokamak and the stellarator.
Continuous versus pulse operation
Conventional power plants generate continuous energy. Several fusion concepts likewise provide for continuous operation ( ). In others, nuclear fusion takes place in pulses, or intermittently. It remains unclear how to trigger successive fusion reactions quickly enough in pulse operation.
State of development
Three criteria give a rough assessment of how much progress is being made with each fusion concept.
Triple product
Product of the plasma density, temperature, and how long the temperature can be maintained without heating. The higher the value, the higher the energy yield from the fusion reaction. The vertical bar indicates the threshold at which a positive energy balance is achieved. The threshold values differ slightly depending on the plasma control.
Status of power plant maturity
A fusion concept with a physically positive energy balance still faces technical obstacles, for example, the total energy balance of the power plant (energy required for magnets, lasers or heating
plasma) or the need for frequent ignitions in the case of pulsed fusion.
Agreement with pioneer concepts
Decades of research have been done on tokamaks and stellarators, as well as on laser fusion at the NIF. The more a concept deviates from these established processes, the less clear it is how long the road to a power plant might be.
