A team of researchers at Lawrence Livermore has successfully combined 9 of the National Ignition Facility’s (NIF’s) 192 laser beams lasers into a superbeam by adding a plasma—a charged mixture of ions and free electrons—to the concept. The team used a Livermore-designed plasma optic to create the superbeam, which produced a directed pulse of light that was nearly four times the energy of any of the individual beams. The research was published in the October 2, 2017, edition of Nature Physics.
Plasma generally creates instabilities when combined with intense laser beams. However, the researchers overcame this obstacle by controlling an instability that causes the transfer of energy when beams cross. “We’ve known that plasma can deflect light and change the direction of energy flow, but it has been difficult to do it in a very precise way,” says Livermore physicist Robert Kirkwood, the lead author on the paper and the programmatic lead for the campaign. “Our results show that by using our new plasma optic, we can now control and predict what the plasma does quite accurately.”
In certain experimental configurations, targets can only be driven by a single beam, which can deliver a limited amount of energy. By combining multiple beams into one, Livermore’s plasma beam combiner can break through that limit and push these experiments into new physics regimes. Beams with high energy and fluence are expected to advance a range of applications including advanced x-ray sources and studies of physics processes occurring at extreme intensities. Looking forward, the team plans to scale up the experiment to 20 beams.
Contact: Robert Kirkwood (925) 422-1007 (firstname.lastname@example.org).
In collaboration with the Scottish Universities Environmental Research Centre, the University of Glasgow, the University of St. Andrews, and the Natural History Museum in London, Livermore researchers have revealed the growth rate of a Martian volcano by dating six meteorites, which formed 1.3 billion to 1.4 billion years ago. The results of the research, which were published online in the October 3, 2017, edition of Nature Communications, indicate that the volcano grew exceptionally slowly—about 1,000 times more slowly than volcanoes on Earth.
Martian volcanoes are the largest in the solar system, and although their size indicates continued activity over billions of years, their formation rates are poorly understood. Using isotopic measurements, the research team, which includes Livermore cosmochemist Bill Cassata, determined that the meteorites are derived from a single volcano and represent at least four eruptions that spanned 90 million years. “The data are consistent with Martian volcanoes being active for much longer than those on Earth, which are typically active for only a few million years,” says Cassata.
The new findings are the first detailed analysis of the eruption rates of volcanoes on Mars using Martian meteorites, which were ejected from the planet by asteroid impact events. The team used recent remapping of the Martian surface by NASA to identify the source of the meteorites and calculate the volcanic growth rate. The research supports evidence that Martian volcanoes date back more than 3.5 billion years and were much more active in the past. Says Cassata, “For Martian volcanoes to get so large,
they must have been far more volcanically active earlier in planetary history.”
Contact: Bill Cassata (925) 423-2812 (email@example.com).
The study of a material’s plasticity (shape) at the most fundamental level rests on understanding how its lattice structure changes during deformation. In a research paper published in the October 25, 2017, edition of Nature, a team of researchers from Lawrence Livermore, the University of Oxford, Los Alamos National Laboratory, the University of York, and SLAC National Accelerator Laboratory reported in situ diffraction experiments measuring deformation twinning at the lattice level during shock compression.
Dislocation-slip (where lattice dislocations are generated and move) and twinning (where sub-grains form with a mirror-image lattice) are the basic mechanisms of plastic deformation. However, until now, diagnosing the active mechanism during the shock has been elusive. In the experiments, the team used a laser to launch a shock wave, in which a laser-heated plasma creates an opposing pressure in the sample. The researchers then probed the state of the sample with an x-ray beam. “The x-rays scatter off the sample at specific angles, forming diffraction rings. The scattering angle provides information on the materials’ structure,” says Livermore physicist and lead author Chris Wehrenberg.
By analyzing the changes of signal distribution within the lines, the team could detect changes in the lattice orientation, or texture, and show whether a material was undergoing twinning or slip. In addition, the team could demonstrate whether the sample twins or slips when shock compressed for most of the entire range of shock pressures. Wehrenberg says, “Our work highlights an untapped area of study, the distribution of signal within diffraction rings, which can yield important information for a variety of applications.”
Contact: Chris Wehrenberg (925) 423-4948 (firstname.lastname@example.org).