By Carl A. Williams
The U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab), in partnership with Ideon Technologies, has received funding from the DOE’s Advanced Research Projects Agency-Energy (ARPA-E) through the Reliable Ore Characterization with Keystone Sensing (ROCKS) initiative. The three-year project aims to secure domestic supplies of critical minerals—materials essential to energy, industry, and national security—by imaging deep beneath the Earth’s surface with precision that conventional sensing techniques cannot match.
At the heart of the project are muons: naturally occurring subatomic particles with extraordinary penetrating power. For years, Ideon Technologies, in collaboration with the mining industry, has used “passive” muons — produced when cosmic rays collide with atmospheric particles — to map ore deposits and understand the Earth’s subsurface. However, because these muons arrive from above, imaging is limited for detectors located below an ore body or geological feature of interest. They also arrive in small numbers — roughly one muon per square centimeter per minute — so forming an image can take several days, weeks, or months of exposure, depending on the depth and imaging resolution required.
The project aims to deliver high-flux muon beams that can be directed at potential imaging targets, including ore bodies, to produce high-resolution 3D images that compress current mineral discovery and characterization timelines from months to hours, thereby accelerating the discovery-to-mine timeline. To create such a source, a high-energy particle accelerator must be compact and mobile enough for field applications.
“Muons with energies around 10 giga electron-volts (GeV) are of great interest because they can penetrate rock, soil, and ore layers up to 20 meters thick; higher-energy muons in the 30 GeV to 100 GeV range can penetrate from 50 meters to over 100 meters,” says Jeroen van Tilborg, a senior scientist and deputy director for experiments at the BELLA Center in Berkeley Lab’s Accelerator Technology & Applied Physics (ATAP) Division, and the project’s principal investigator.
This “active” muon source is enabled by laser plasma accelerators pioneered at BELLA, a state-of-the-art laser facility within the ATAP Division. These systems use intense, ultrashort laser pulses to displace electrons in a plasma, creating an electrostatic wave — known as a wakefield — that produces accelerating fields orders of magnitude higher than those achievable in conventional accelerators. These wakefields can accelerate electron beams to multi-GeV energies over centimeter-scale distances. The electrons are then directed at a solid target, where they generate muon beams that are three to four orders of magnitude more intense than the natural flux while preserving the energy of the incoming electrons.
“Producing the high-charge, high-energy electron beam drivers needed to produce a muon beam is exactly where compact laser-plasma accelerators (LPAs) could excel, thanks to their ultra-high accelerating gradients and compactness,” says van Tilborg.
Berkeley Lab has already demonstrated single-stage acceleration of a 10-GeV electron beam over 30 centimeters. This project now aims to couple two approximately 6-GeV LPA stages to achieve more than 12 GeV of acceleration. Achieving and de-risking this multi-stage proof of concept will validate the technical path to the 30-GeV systems required to penetrate 50 meters of rock and to the 100-GeV systems capable of sensing through 150 meters.
“Years of investment in LPA research at Berkeley Lab have produced the technologies that make this project possible,” says Anthony Gonsalves, a staff scientist at ATAP who leads the accelerator work and serves as the experimental lead for the new muon project. “This project is an exciting opportunity to translate decades of accelerator research into technology that addresses an important national need by developing reliable systems to deliver the high-energy muons required for practical subsurface imaging.”
The key to achieving this two-stage acceleration is to couple the stages with an active plasma lens that refocuses the high-energy electron beam as it exits one stage and enters the next, and with a highly reflective plasma mirror that preserves the laser’s properties, enabling it to effectively drive the plasma wakefield in the next stage. Together, these components allow the electron beam to pass from stage to stage, gaining energy at each stage, which is essential for producing the deeply penetrating muons needed for high-resolution subsurface mineral imaging of the deepest geological targets.
The project draws on the complementary strengths of its three partners. ATAP is the hardware lead, applying its expertise in laser-plasma interactions and high-fidelity Particle-In-Cell simulations to develop a two-stage, 12-GeV electron source. Ideon Technologies is the world leader in muon tomography and advanced data-fusion capabilities for the mineral exploration and mining industry, including proprietary muon detector arrays, physics simulations, and geological software. That software transforms raw data into 3D mass-density visualizations, enabling geologists to “see” mineral deposits and structural anomalies at meter-scale resolution. Drawing on decades of experience with high-energy particle-collider detectors, Berkeley Lab’s Physics Division will provide muon instrumentation and particle-tracking diagnostics to optimize the muon beam.
“The critical minerals challenge demands faster, better ways to understand and develop the resources society urgently needs. With the outcomes from this project, physics more advanced than that of the world’s largest particle accelerators will now image millions of cubic feet of rock in hours, not months,” says Ideon Chief Technology Officer Douglas Schouten. “Working with world-leading research institutes like Berkeley Lab, Ideon is taking that frontier capability out of the lab and combining it with advanced sensing and the penetrating power of subatomic particles to unlock real value for the industries society depends on.”
By combining Berkeley Lab’s expertise in advanced accelerators with Ideon’s commercial and advanced quantum-sensing capabilities, the project could lay the groundwork for faster, more accurate, and cost-effective mineral resource characterization, thereby accelerating U.S. domestic critical mineral development and strengthening supply chains for energy, industry, and national security. The technology’s promise also extends beyond mining. It could identify underground voids, gaps, and caves, offering significant advantages for civil engineering and industrial safety, with implications for national security and critical infrastructure.
“By pioneering the development of a deeply penetrating, portable muon source, this project ensures that the U.S. maintains leadership in critical mineral resources vital to energy and the economy, leveraging technologies developed through pioneering accelerator and detector R&D,” says ATAP Division Director Cameron Geddes.