Scientists have designed a pinhole camera-like device that can withstand the 100-million-degree heat in fusion reactors to provide invaluable data that could boost the output of future fusion power plants.
Generating heat and energy from fusion reactions requires carefully manipulating plasma, the electrically charged fourth state of matter that makes up 99% of the visible universe.
Now, scientists at the US Department of Energy (DOE)’s Princeton Plasma Physics Laboratory (PPPL) say they have finished building a new plasma measurement instrument that could help realise the transformative potential of fusion for the energy transition.
Fusion uses the same process that generates light and heat from stars, fusing hydrogen and other light elements to release huge amounts of power that pioneers in the sector hope to tap for unlimited zero-carbon electricity.
The new device, known as ALPACA, is PPPL said “akin to a pinhole camera.”
ALPACA has been used to observe light emitted by a halo of neutral atoms surrounding the plasma inside DIII-D, a tokamak reactor that US energy and defence firm General Atomics operates for the DOE in San Diego.
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Tokamak reactors are shaped like doughnuts and use huge magnets that are used to contain plasma hotter than the surface of the sun.
Along with stellarators, tokamaks are one of the two mainstream fusion approaches that have been the focus of the majority of fusion research in recent decades.
By studying this light emitted in tokamaks, PPPL said scientists can “glean information about the neutral atoms’ density that could help them keep the plasma hot and increase the amount of power generated by fusion reactions.”
ALPACA helps scientists study a process known as fueling. During this process, clouds of neutral atoms of varying densities around the plasma break apart into electrons and ions and enter the plasma.
“We’re interested in fueling because neutral atom density can increase plasma particle density, and plasma density affects the number of fusion reactions,” said Laszlo Horvath, a PPPL physicist who helped design and install ALPACA.
“If we can increase the plasma’s density, then we can have more fusion reactions, which generate more fusion power. That’s exactly what we want to have in future fusion power plants.”
The nearly 2-foot-long ALPACA device collects plasma light that has a specific property known as the Lyman-alpha wavelength, said PPPL. From this, researchers can calculate the neutral atoms’ density by measuring the light’s brightness.
Previously, PPPL said scientists have “inferred the density from measurements taken by other instruments, but the data has been hard to interpret.”
“When we are running experiments on machines like DIII-D, we need to understand what is going on inside the device, especially if we want to boost its performance,” said Horvath.
“But because the plasma is at 100 million degrees Celsius, we can’t just use an oven thermometer or anything conventional,” he said. “They would just melt.”
“Diagnostics give us knowledge about what would otherwise be a black box.”