Overview of the Interdisciplinary Physics Experiment 1 in Support of Low Yield Nuclear Monitoring

We describe a series of multi-physics experiments, referred to as Physics Experiment 1 (PE1) underway at the United States' Nevada National Security Site (NNSS). PE1 was designed to address fundamental science questions related to explosion monitoring, identifying distinct signatures of chemical explosions and differences between coupled and decoupled explosions. In addition, we seek to understand how multimodal observables vary with data type, distance, and other parameters and how data fusion across these observables may improve determination of source type and emplacement conditions. Each detonation includes tracers, a network of sensors to record seismic, acoustic, and electromagnetic waves, measurement of atmospheric conditions, and air sample collection for measurement of tracer concentration. Additionally, there are related experiments, focused upon individual modalities that employ well-characterized sources. Most recently, the fully coupled detonation experiment, PE1-A was conducted and excellent data return was achieved. We provide an overview of observations from PE1-A and results from some initial analyses. Some of our observations confirm prior expectations, while others provide surprising lessons learned from the multimodal data acquired. The results highlight the importance of performing large field experiments at scale that include interdisciplinary teams addressing the impact of multiple modalities. The project includes a sophisticated data management plan, and the PE1-A data will be released to the public in 2026.