Unique Application of High Energy Density Plasmas for Nuclear Astrophysics Experiments

This award supports a study of how the nuclei of chemical elements are formed in astrophysical environments by using high energy lasers in a laboratory. Nuclear reactions play key roles in the dynamics and evolution of our universe. They are responsible for forming the basic elements that make up everything we see around us – including the simplest hydrogen atoms, the oxygen we breathe, metals such as iron and heavy elements such as uranium - through nucleosynthesis processes in stars and during the Big Bang.

However, nuclear reactions cannot be measured directly in space. To solve outstanding questions about abundances of elements in the universe, we have to know how these reactions happen under different conditions. Historically, experiments to test the likelihood of different reactions have been done using accelerators.

However, accelerators use solid or gaseous targets. In stars, matter is found in a plasma state, where the atoms are split into their charged constituents, ions and electrons. Scientists have reasons to believe that reaction probabilities will be different in plasmas compared to solid or gaseous targets.

The present work uses large lasers, such as the National Ignition Facility (NIF), to create plasmas where the reactions can be studied in an environment comparable to that in stars. The project will support an international collaboration with Imperial College London and Lawrence Livermore National Laboratory (LLNL), training of graduate students and a postdoc, and may advance the development of fusion energy and contribute to national security.

This effort is expected to improve the understanding of how elements are formed in the universe by answering questions about plasma effects on nuclear reaction probabilities that have never before been addressed experimentally. In doing so, it will contribute to the goals of NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" meta-program.

The project focuses on the use of high-energy-density (HED) plasmas for basic nuclear science experiments relevant to nuclear astrophysics. High energy laser facilities such as OMEGA at the University of Rochester and the NIF at LLNL can create the stellar-like HED experimental conditions in a laboratory setting. Unlike the more traditional accelerator-based approached, the laser-driven HED conditions more closely mimic astrophysical environments in several ways, including thermal distributions of the reacting ions as opposed to monoenergetic ion beams; stellar-relevant plasma temperatures and densities; and, in the case of NIF, neutron flux densities not found anywhere else on earth.

This represents a unique opportunity for understanding plasma effects on nuclear reactions. Fully exploiting this platform for nucleosynthesis experiments is anticipated to be a broad, decades-long effort. The goal of the current effort is to advance the frontier through new experimental projects.

In particular, four areas will be addressed: (1) using new diagnostic capabilities to uniquely study six-nucleon systems with three particles in the final state, such as those relevant to the solar proton-proton cycles; (2) development of a platform for studying reactions involving mid-Z ions relevant to the stellar carbon-nitrogen-oxygen (CNO) catalyzed proton-burning cycles; (3) making strides toward the first terrestrial measurements of plasma screening of nuclear reactions; and (4) development of a platform for use of high-performing NIF implosions to study neutron capture on nuclei in excited states.

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.