South Korea Plans Next-Gen Underground Lab to Unlock Stellar Evolution and Cosmic Secrets

A kilometer beneath Mount Yemi in South Korea's Gangwon Province, scientists are building two instruments that will peer deeper into the mechanics of stars and the nature of the universe itself. Yemilab, a multipurpose underground research facility buried 1,009 meters below the mountain's summit, is the site of an ambitious dual project: YUNA@K, an accelerator designed to recreate the nuclear reactions that power stars, and νEYE, a detector engineered to capture the ghostly particles that stream from the Sun's core.

The choice of location is not incidental. At that depth, the surrounding bedrock acts as a shield, blocking the constant rain of cosmic rays that bombard Earth's surface. This creates an environment where rare, faint particle interactions can be isolated and studied—a prerequisite for the kind of precision physics both instruments demand. Senior Engineer So Jung-ho at the Institute for Basic Science (IBS) Yemilab is leading the accelerator project, while Director Kim Young-deok of IBS's Center for Underground Physics oversees the neutrino detector. Together, they are positioning South Korea to lead a field that has, until now, been dominated by a handful of facilities scattered across the globe.

YUNA@K stands for Yemi Underground Nuclear Astrophysics at Korea. The accelerator will work by firing protons and alpha particles at targets with enough energy to trigger the fusion reactions that occur inside stars. Currently, only three underground accelerators operate worldwide: CASPAR in the United States, LUNA in Italy, and JUNA in China. LUNA, Italy's flagship facility, can accelerate protons to energies of approximately 3.5 megaelectron volts. So's design targets 6 megaelectron volts for protons and 9 megaelectron volts for alpha particles—energies that no existing underground facility has reached. The significance lies not in raw power but in what becomes possible at those energies. As nuclei gain speed, they can overcome the Coulomb barrier, the electromagnetic repulsion that normally keeps positively charged atomic nuclei apart. This allows researchers to study nuclear reactions involving carbon and oxygen, elements with higher Coulomb barriers that have never been thoroughly examined in laboratory conditions. Understanding these reactions is essential to understanding how stars evolve and how the heavy elements that make up planets and life itself are forged.

So is already in conversation with leading Korean nuclear physicists, including Cheon Myung-ki at Soongsil University's Center for Extreme Nuclear Astrophysics and Ahn Jung-keun at Korea University, to shape the research agenda. The accelerator's design compensates for the space constraints of an underground environment by increasing the particle beam current rather than the acceleration section length—a practical solution that allows higher collision rates and more observable reactions.

The second instrument, νEYE, tackles a different frontier. Neutrinos are among the most elusive particles in physics: they carry no electric charge, possess almost no mass, and interact so weakly with matter that trillions pass through human bodies every second without leaving a trace. They are born in the Sun's fusion reactions, in supernovae, and in nuclear reactors. Detecting them requires extraordinary sensitivity and isolation from background noise. νEYE will occupy a large cylindrical chamber roughly 20 meters in diameter and depth within Yemilab, filled with approximately 2 kilotons of organic solvent rather than water. This choice of medium matters. Japan's Super-Kamiokande and the planned Hyper-Kamiokande use water and the Cherenkov method, detecting the blue light emitted when charged particles travel faster than light through water. νEYE employs the liquid scintillator method instead, capturing the brief flashes of light produced when neutrinos interact with particles in the oil. This approach allows for greater sensitivity to lower-energy events, particularly solar neutrinos—the particles streaming directly from the Sun's core that carry information about its internal structure and fusion processes.

Director Kim has submitted the νEYE proposal to South Korea's Ministry of Science and ICT as a large-scale infrastructure research project. He emphasized that the goal is to observe neutrino energies and properties that existing detectors have not adequately studied, with particular focus on solar neutrinos. The precision measurements νEYE could achieve would provide crucial data for understanding how the Sun works at its most fundamental level.

Yemilab has already established itself as a hub for underground physics, hosting dark matter search experiments. With YUNA@K and νEYE now under development, the facility is positioned to become a center of gravity for fundamental physics research globally. The two instruments complement each other: one recreates the nuclear processes that occur in stars, the other observes the particles those processes emit. Together, they promise to illuminate questions about stellar evolution, cosmic origins, and the nature of matter itself—questions that have occupied physicists for generations but have remained beyond the reach of existing technology.