Scientists from the French Alternative Energies and Atomic Energy Commission (CEA) made a landmark achievement by sustaining a fusion reaction for six minutes while injecting 1.15 gigajoules of energy into it.
Nuclear Fusion as an Energy Source
Nuclear fusion reactions power the Sun and other stars. Once harnessed, it has the potential to be an almost unlimited, safe, and CO2-free energy source on Earth.
Unlike nuclear fission, this technology does not generate nuclear waste, which needs to be disposed of properly. Fusion is also a reliable, carbon-free energy source that can be switched on and off.
The process takes place inside donut-shaped reactors known as tokamaks, which resemble the reaction conditions in the Sun. Inside the tokamaks, hydrogen is heated to 122 million degrees Fahrenheit (50 million degrees Celsius) to produce the fourth state of matter or plasma.
To make this technology economically feasible, experts are facing the challenge of generating an energy output that would far exceed the energy input. Scientists believe that this can be achieved by confining the plasma for long durations, known as shots, and lining the fusion reactor with tungsten.
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Lining a Tokamak With Rare Metal
Scientists at CEA explore the use of tungsten in a fusion reactor at its tungsten Environment in Steady-state Tokamak (WEST) reactor in France. In previous experiments, fusion reactors achieve longer shots by using graphite on the reactor walls.
Carbon-based material is easier to work with, but it may not be practical for larger-scale reactors since the fuel is retained in the walls. Meanwhile, tungsten does not retain any fuel but it is tricky to work with because it can rapidly cool down the plasma even if small amounts get in.
Working with such a challenging material can fail when conventional tools are used. To address this challenge, Switzerland-based DECTRIS creates an X-ray-based diagnostic tool to measure plasma radiation and help researchers measure properties like core plasma temperature.
The diagnostic tool is known to use all its pixels to simultaneously measure energy levels. It was even further configured by researchers from US-based Princeton Plasma Physics Laboratory (PPPL) to enable each pixel to measure energy levels independently.
The newly configured diagnostic tool was used by PPPL researchers to confirm the reaction conditions in WEST. They also noted that the plasma had 15% more energy and twice the density than before, conditions that are both important in generating reliable power output.
According to PPPL researcher Tullio Barbui, the team was able to measure the central electron temperature during the six-minute shot. It was observed in a very steady state of 4 kilovolts, which is a pretty remarkable result. Additionally, the detector can be configured to measure the same plasma with as many energies as possible.
As described by CEA scientist Xavier Litaudon, it is extremely challenging to operate a facility with a tungsten-line wall, but thanks to the new measurements, scientists finally have the ability to measure this rare metal inside the plasma and understand the transport of this element from the wall to the plasma core.
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