Scientists at the U.S. Department of Energy’s Princeton Plasma Physics Laboratory (PPPL) have completed the construction of a new plasma measurement instrument called ALPACA. This diagnostic tool could help increase the heat of fusion reactions in tokamaks, potentially improving the power output of future fusion power plants.
Understanding Neutral Atom Density for Better Fusion Reactions
ALPACA observes the light emitted by a halo of neutral atoms surrounding the plasma inside DIII-D, a tokamak operated by General Atomics in San Diego. By studying this light, scientists can gather information about the neutral atoms’ density, which could help them keep the plasma hot and boost the power generated by fusion reactions.
“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 stationed at DIII-D who helped coordinate ALPACA’s assembly and installation. “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.”
ALPACA and LLAMA: A Complementary Pair
ALPACA is one of a pair of diagnostics, with its twin called LLAMA (Lyman-alpha measurement apparatus). While LLAMA observes the inner and outer regions of the lower part of the tokamak, ALPACA observes the inner and outer regions of the upper part.
“We need both devices because although we know that neutral atoms surround the plasma, the number of neutral atoms varies from place to place, so we don’t know exactly where they accumulate,” said Alessandro Bortolon, PPPL principal research physicist who heads the PPPL collaboration with the General Atomics DIII-D National Fusion Facility in San Diego. “Because of that, and because we can’t extrapolate from single measurements, we have to measure in multiple locations.”
ALPACA’s design incorporated 3D printing, allowing for the integration of a hollow chamber inside the main structural backbone for cooling conduits. The diagnostic is currently being tested and will start taking actual measurements once DIII-D resumes operations after a period of maintenance.
Keyword/phrase: ALPACA plasma diagnostic
