Study of Nonthermal Electron Driven Warm Dense Plasmas Using X-ray Free Electron Lasers

This award supports a study of the fundamental properties of warm dense matter (WDM), a poorly understood plasma state of matter made of electrons and ions at high density and relatively low temperature. The focus of the study will be on WDM formed under the influence of unusually energetic “non-thermal” electrons. These electrons travel at nearly the speed of light, penetrate deep into dense plasma, and change how energy is transported and how matter is heated under extreme conditions. A better understanding of these processes is important for both natural and laboratory systems, including solar and stellar plasmas and the efforts to develop sources of fusion energy here on Earth. Progress has been limited because WDM is difficult to model and to investigate experimentally as the material enters a poorly understood state between an ideal plasma and condensed matter. Existing theories do not yet fully describe this regime, and precise experimental data remain limited. To address these limitations, non-thermal-electron-driven WDM will be created with a high-power, short-pulse laser and probed using ultrashort hard X-ray pulses from X-ray free-electron lasers (XFELs). The project will provide training opportunities for graduate and undergraduate students at cutting-edge XFEL facilities in the United States, Japan, and Germany. The goals of this project are to determine the transient plasma conditions in non-thermal-electron-driven warm dense matter through spatially and temporally resolved XFEL-based measurements. A solid-density foil will be isochorically heated by laser-driven non-thermal electrons generated by a relativistic-intensity, femtosecond laser. The plasma conditions of the heated foil will be diagnosed using X-ray Thomson scattering (XRTS) and X-ray transmission imaging. To achieve these goals, the project will develop and deploy a radiation-hardened, high-collection-efficiency X-ray spectrometer for single-shot XRTS and establish near-K-edge X-ray transmission imaging as a complementary diagnostic for dense plasmas. These high-precision data will be used to build and benchmark reliable physics models describing how nonthermal electrons partition energy during warm dense matter formation and to enable direct comparisons with particle-in-cell and quantum molecular dynamics simulations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2607313 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Hiroshi Sawada | Institution: Board of Regents, NSHE, obo University of Nevada, Reno, RENO, NV | Award Amount: $639,322 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2607313 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2607313.html