Newswise — An international team of scientists has discovered a new way to advance fusion energy by increasing understanding of the properties of dense, warm matter, an extreme state of matter similar to that found in the cores of giant planets such as Jupiter. The results, led by Sophia Malko of the US Department of Energy’s (DOE) Princeton Plasma Physics Laboratory (PPPL), detail a new technique for measuring the “stopping force” of nuclear particles in plasma using an ultrafast, high-repetition laser. Understanding the proton’s stopping power is particularly important for integrating into self-confinement (ICF).
Running sun and stars
This process contrasts with the creation of fusion at PPPL, which heats plasma to temperatures of up to a million degrees in magnetic confinement facilities. Plasma, the hot, charged state of matter made up of free electrons and atomic nuclei or ions, fuels fusion reactions in both types of research, aimed at reproducing the fusion that powers the sun and stars as a safe and clean source. and nearly limitless power to generate electricity in the world.
The “stopping force” is a force that acts on charged particles due to the collision of electrons in the material resulting in a loss of energy. “For example, if you don’t know the stopping power of a proton, you can’t calculate the amount of energy deposited in the plasma, and therefore design the laser at the appropriate energy level to create fusion ignition,” said Malko, lead author of a research paper outlining the the findings in Nature Connections. “Theoretical descriptions of the stopping ability in a material with a high energy density and especially in a difficult warm dense material, and measurements are largely missing,” she said. “Our paper compares experimental data for the energy loss of a proton in a warm, dense material with theoretical models for power off.”
The Nature Connections The investigation investigated the power to stop the proton in a largely unexplored system using low-energy ion beams and warm, dense laser-produced plasmas. To produce the low-energy ions, the researchers used a special magnetic device that selects the low-energy constant-energy system from a broad proton spectrum generated by the laser-plasma interaction. The selected beam then passes through a warm, dense laser-driven material and its energy loss is measured. The theoretical comparison with the experimental data showed that the closest matched sharply with the classical models.
Instead, the closest agreement came from recently developed first-principle simulations based on a multibody or interacting quantum mechanical approach, Malko said.
Accurate stop measurements
The precise stop measurements could also advance the understanding of how protons produce what is known as rapid ignition, an advanced scheme from self-confinement fusion. “In rapid proton-driven ignition, where the protons have to heat the compressed fuel from very low to high temperature states, the proton’s stopping power and the state of the material are tightly related,” Malko said.
She explained that “the stopping force depends on the density and temperature of the state of matter,” both of which are in turn influenced by the energy deposited by the proton beam. “Consequently, the uncertainty in the stopping power leads directly to the uncertainty in the total proton and laser energy required for ignition,” she said.
Malko and her team are conducting new experiments at the Department of Energy laserentos at Colorado State University to extend their measurements to the so-called Bragg peak region, where maximum energy loss occurs and where theoretical predictions are uncertain.
This paper was co-authored by 27 researchers from the United States, Spain, France, Germany, Canada and Italy.
Support for this work comes from the Department of Energy’s National Nuclear Security Administration along with the Los Alamos National Laboratory (LANL) Laboratory Directed Research and Development Program and from the European and Spanish Ministries. The experiments were conducted at the VEGA II laser facility in Spain where the German target laboratory GSI prepares and delivers samples for targets. Computing was provided by Enterprise Computing and LANL Advanced Scientific Computing Programs.
PPPL, at Princeton University’s Forrestal Campus in Plainsboro, New Jersey, is dedicated to creating new knowledge about plasma physics – extremely hot and charged gases – and to developing practical solutions for creating fusion energy. The lab is managed by the university for the US Department of Energy’s Office of Science and is the largest supporter of basic research in the physical sciences in the United States and works to address some of the most pressing challenges of our time. For more information visit energy.gov/science.