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The DOE Science News Source is a Newswise initiative to promote research news from the Office of Science of the DOE to the public and news media.
  • 2017-12-19 15:05:01
  • Article ID: 687106

Proton-Proton Fusion: Powering the Sun

Large-scale simulations of quarks promise precise view of reactions of astrophysical importance.

  • Credit: Image courtesy of William Detmold

    Two protons (green), after “tunneling’’ through their repulsive electrostatic barrier and undergoing weak and strong interactions, fuse together to produce a deuteron (the lightest nucleus) (yellow), a positron, and a neutrino.

The Science

The fusion of two protons initiates the primary nuclear cycle that powers the Sun. The rate of this low-energy, weak-interaction fusion is too small to be measured in the laboratory. While nuclear model predictions for this reaction are impressive, calculations without models would reduce uncertainties and offer a more accurate view of proton-proton fusion and related processes. Using a technique called lattice quantum chromodynamics, scientists performed the first successful model-independent calculation of the proton-proton fusion rate directly from the fundamental dynamics of quarks and gluons (the building blocks of protons and nuclei).

The Impact

This work paves the way to calculate the rate of proton-proton fusion, and similar nuclear reactions of astrophysical importance, with new levels of precision.

Summary

The Nuclear Physics with Lattice Quantum Chromodynamics Collaboration (NPLQCD), under the umbrella of the U.S. Quantum Chromodynamics Collaboration, performed the first model-independent calculation of the rate for proton-proton fusion directly from the dynamics of quarks and gluons using numerical techniques. The rate of this process is too small to be measured in the laboratory today for two reasons: the electrostatic repulsion between the low-energy protons and the small weak interaction rates. The team achieved the theoretical prediction for this process through calculations in which electrostatic repulsion was removed and the weak interaction rates were increased to provide access to the critical elements of the process. These were then restored using systematic approximations to the underlying physical theory (effective field theory techniques) in making the prediction for the reaction rate. The first lattice quantum chromodynamics calculation of the strength of the weak transition between the triton and helium-3 (which carry significant information of spin interactions in nuclear medium) was also performed in this work and found to be consistent with experimental measurements. These calculations used lattice quantum chromodynamics, a technique in which space-time is represented by a finite grid of points, and the quantum fields describing the quarks and gluons are defined on these points and the links between them, respectively. This method provides an evaluation of the quantum chromodynamics path integral, through Monte Carlo sampling of the quantum mechanical motion of the quarks and gluons (the subatomic particles that bind the quarks together). This method is completely controlled and can be systematically improved and refined by reducing the physical distance between the grid points, by increasing the volume of space-time, and by increasing the sampling of the path integral. This work used configurations (“snapshots” of the quantum-mechanical vacuum) generated using the Chroma software suite developed within DOE’s Scientific Discovery through Advanced Computing funded U.S. Quantum Chromodynamics Collaboration. Existing algorithms and code for forming nuclear correlation functions in lattice quantum chromodynamics calculations and new algorithms including the interactions of quarks with external probes, developed within NPLQCD, were used to calculate the key quantities that determine the rate for proton-proton fusion. The results of these calculations were connected to nature using effective field theory techniques. Understanding gained in NPLQCD’s calculations of the thermal neutron capture process n+p→d+γ was used in making this connection. With increased computational resources, these calculations can be systematically refined to provide an uncertainty in the rate for proton-proton fusion, and similar nuclear reactions, which is significantly smaller than is possible with other techniques. This breakthrough was made possible by algorithmic developments and high-performance supercomputing resources.

Funding

This work was supported in part by the U.S. Department of Energy, Office of Science; National Science Foundation; and the Kavli Institute.

Publications

M.J. Savage, P.E. Shanahan, B.C. Tiburzi, M.L. Wagman, F. Winter, S.R. Beane, E. Chang, Z. Davoudi, W. Detmold, and K. Orginos, “Proton-proton fusion and tritium beta-decay from lattice quantum chromodynamics.” Physical Review Letters 119, 062002 (2017). [DOI: 10.1103/PhysRevLett.119.062002]

S.R. Beane, E. Chang, W. Detmold, K. Orginos, A. Parreño, M.J. Savage, and B.C. Tiburzi, “Ab initio calculation of the np→dγradiative capture process.” Physical Review Letters 115, 132001 (2015). [DOI: 10.1103/PhysRevLett.115.132001]

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Columbia investigators have made a major breakthrough in nanophotonics research, with their invention of a novel "home-built" cryogenic near-field optical microscope that has enabled them to directly image, for the first time, the propagation and dynamics of graphene plasmons at variable temperatures down to negative 250 degrees Celsius. If researchers can harness this nanolight, they will be able to improve sensing, subwavelength waveguiding, and optical transmission of signals.

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A piezoelectric ceramic foam supported by a flexible polymer support provides a 10-fold increase in the ability to harvest mechanical and thermal energy over standard piezo composites, according to Penn State researchers.


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Power to the People

The University of Utah College of Engineering has received a $2 million grant to create a laboratory and develop new technology for communities with backup power sources, known as microgrids, so they can quickly and more securely operate in the event of a massive power outage due to a natural disaster or cyberattack.

The U. S. Department of Energy Announces $34 Million for Small Business Research and Development Grants

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Sandia National Laboratories will receive $10.5 million from the Department of Energy to research and design a cheaper and more efficient solar energy system.The work focuses on refining a specific type of utility-scale solar energy technology that uses mirrors to reflect and concentrate sunlight onto a receiver on a tower.

Solar Turbines, Inc. Selects Penn State to Establish Center of Excellence in Gas Turbines

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ORNL Facility Receives American Nuclear Society's Historic Landmark Designation

The American Nuclear Society has designated the Radiochemical Engineering Development Center at the Department of Energy's Oak Ridge National Laboratory an ANS Nuclear Historic Landmark, recognizing more than 50 years of isotope production and nuclear fuel cycle research.

Steven Cowley named director of DOE's Princeton Plasma Physics Laboratory

Steven Cowley, a theoretical physicist and international authority on fusion energy, has been named director of the U.S. Department of Energy's (DOE) Princeton Plasma Physics Laboratory (PPPL), effective July 1.

Scientists Turn X-ray Laser Into World's Fastest Water Heater

Scientists have used a powerful X-ray laser at the Department of Energy's SLAC National Accelerator Laboratory to heat water from room temperature to 100,000 degrees Celsius in less than a tenth of a picosecond, or millionth of a millionth of a second.

PNNL Part of a New National Center for Near-Atomic Resolution of Biological Molecules

A collaboration between the Pacific Northwest National Laboratory and Oregon Health & Science University has been chosen as a national center for a Nobel Prize-winning method of imaging, cryo-electron microscopy, that is revolutionizing structural biology.

SLAC Will Open One of Three NIH National Service Centers for Cryo-Electron Microscopy

The National Institutes of Health announced today that it will establish a national service and training center for cryogenic electron microscopy research at the Department of Energy's SLAC National Accelerator Laboratory.

Planck Collaboration Wins 2018 Gruber Cosmology Prize

The Planck Team--including researchers in Lawrence Berkeley National Laboratory's (Berkeley Lab's) Computational Research and Physics divisions--have been awarded the 2018 Gruber Cosmology Prize.


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The Secret to Measuring an Antineutrino's Energy

Scientists are developing better models that describe both neutrino and antineutrino data, which can offer insights into the nature of the universe.

How to Cope with Cases of Mistaken Identity: MINERvA's Tale of Pions and Neutrinos

Neutral pion production is a major character in a story of mistaken identity worthy of an Agatha Christie novel.

Perfecting the Noise-Canceling Neutrino Detector

MicroBooNE neutrino experiment cuts through the noise, clearing the way for signals made by the hard-to-detect particle.

Keeping Tabs on Polysulfides in Batteries

Optimizing lithium-sulfur battery electrolytes for long life.

Huge "Thermometer" Takes Temperatures of Tiny Samples

New spectroscopic technique measures heat in itty-bitty volumes that could reveal insights for electronics and energy technology.

Water, Water, Everywhere, but How Does It Flow?

Scientists use new X-ray technique to see how water moves at the molecular level.

Magnetized Plasmas That "Twist Light" Can Produce Powerful Microscopes and More

A non-twisting laser beam moving through magnetized plasma turns into an optical vortex that traps, rotates, and controls microscopic particles, opening new frontiers in imaging.

Whistling While You Work: Fusion Scientists Find Inspiration in Atmospheric Whistles

Just like lightning, fusion plasmas contain odd electromagnetic whistler waves that could control destructive electrons in fusion reactors.

Zero Tolerance in Tokamaks: Eliminating Small Instabilities Before They Become Disruptions

Energetic ions and beam heating cause or calm instabilities, depending on the tokamak's magnetic field.

MURR Becomes First Reactor Facility to Join DOE's Isotope Program

DOE and MURR partner to ensure scientists have access to essential research isotopes.


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