A tungsten-lined tokamak reactor operated by the French Alternative Energies and Atomic Energy Commission (CEA) has set a new fusion record by sustaining the plasma for six minutes and injecting 1.15 gigajoules of energy into it.
The US-based Princeton Plasma Physics Laboratory (PPPL) confirmed these measurements in a press release.
Nuclear fusion is literally the hottest energy source, hoping to break into the market. Unlike its fission counterpart, the technology does not generate nuclear waste that needs to be properly disposed of and is a reliable, carbon-free source of energy that can be switched on and off at will.
Inside the donut-shaped reactors called tokamaks, scientists create reaction conditions that resemble those of the Sun. Hydrogen is heated to 50 million degrees Celsius to create the fourth state of matter—plasma.
The challenge in making this technology economically feasible is generating an energy output far exceeding what has been put into generating the plasma. Scientists agree that the way to achieve this is by confining the plasma for long durations, also known as shots, and lining the tokamak with tungsten, which can help.
Tungsten-lined tokamak
The CEA is exploring the use of tungsten in a fusion reaction at its tungsten (W) Environment in Steady-state Tokamak (WEST) reactor in France. Fusion reactors previously achieving longer shots have used graphite on the reactor walls.
While the carbon-based material is easier to work with, it may not be feasible for larger-scale reactors since it retains the fuel in the walls. Conversely, tungsten does not retain any fuel but is tricky to work with since it can rapidly cool down the plasma even if minute amounts get in.
While comparing the two materials, Luis Delgado-Aparicio, the lead scientist of physics research at PPPL, said, “This is, simply, the difference between trying to grab your kitten at home versus trying to pet the wildest lion.”
A novel diagnostic
Conventional tools can fail when working with such a challenging material. Switzerland-based DECTRIS makes an X-ray-based diagnostic tool that measures plasma radiation. This tool can help researchers determine properties such as core plasma temperature.
While this tool is set to use all its pixels to measure energy levels simultaneously, the PPPL researchers further configured it so that each pixel could measure energy levels independently.
The PPPL researchers used this newly configured diagnostic tool to confirm the reaction conditions in WEST.
During this achievement, the researchers confirmed that the plasma had 15 percent more energy and twice the density than before, both conditions necessary to generate reliable power output.
“During the six-minute shot, we were able to measure quite nicely the central electron temperature. It was in a very steady state of around 4 kilovolts. It was a pretty remarkable result,” said Tullio Barbui, a PPPL researcher involved in this work.
“This detector has the unique capability of being configured to measure the same plasma with as many energies as you want.”
“It’s extremely challenging to operate a facility with a tungsten wall,” added Xavier Litaudon, a CEA scientist, in the press release.
“But thanks to these new measurements, we will have the ability to measure the tungsten inside the plasma and to understand the transport of tungsten from the wall to the core of the plasma.”
The researchers plan to publish their findings in the coming few weeks.
