December 26, 2018
The NIF & Photon Science Directorate was well represented at the recent 60th annual American Physical Society (APS) Division of Plasma Physics meeting, which included invited talks on topics ranging from predictive inertial confinement fusion (ICF) models to the first proton beams accelerated by NIF’s Advanced Radiographic Capability (ARC).
Ten invited talks from LLNL’s ICF and High Energy Density Science programs were highlighted at the influential conference, held in early November in Portland, Oregon.
Those and other presentations by Lab scientists and researchers drew attentive crowds. “The APS community is quite interested in our progress in ICF and other plasma physics work,” said ICF Physics Integration Lead Pravesh Patel.
The conference’s normally quick pace and the large number of LLNL-related presentations means Lab representatives often miss each other’s talks. So, many of the Lab’s attendees gathered again a month later (in the B481 atrium) for an APS Social. The annual post-APS event, coordinated this year by physicist Art Pak, gives conference goers a second chance to share their posters and work.
The APS invited talks included one by LLNL physicist Jim Gaffney, who discussed the experimental design process in a presentation titled, “Making ICF Models More Predictive: Combining Simulations, Experiments and Expert Knowledge using Machine Learning and Bayesian Statistics.”
“I showed how we can build a model that matches multiple experimental observables and explains the observed performance in terms of physical degradation mechanisms,” Gaffney said. “By doing that for a series of NIF shots, we can build a statistical model that allows us to predict the performance of future experiments.”
NIF has used that model, Gaffney explained, to compare different potential higher-yield paths in “Bigfoot” shot campaigns, which combines ultra-short, high-energy laser pluses with a strong initial shock, or foot, to drive target capsule implosion.
The talk stimulated “very interesting discussions with people from a wide range of institutions,” he said.
In another invited presentation, ICF Chief Scientist Omar Hurricane gave an overview of the experimental steps being taken as NIF approaches the burning plasma stage on the road to achieving ignition. Those steps include testing the use of smaller fuel fill tubes and capsule mounts, as well as larger hohlraums and fuel capsules.
He also provided a new analytic condition to describe burning plasma and introduced an analytic solution method for the non-linear increase in implosion stagnation pressure and yield due to heating by alpha particles.
Siegfried Glenzer, a professor and high energy density division director at SLAC National Accelerator Laboratory, attended the presentation.
“It is great to see how hot-spot performance has improved over the last couple of years,” he said. “The team has a good understanding of what needs to get done next to make continued progress toward ignition. Besides improving the capsule mounting, it will be important to increase the capsule energy absorption. We hope to see the results of these efforts soon.”
In addition, Lab post-doctoral researcher Derek Mariscal gave a presentation on NIF’s ARC-accelerated proton beams, reporting on research into a powerful new source of high-energy protons at the petawatt-class laser system.
Mariscal said he explained the capability to model “the entire laser-accelerated ion process and explain why we achieved maximum proton energies that were significantly beyond what was conventionally expected based on scalings from over a decade of previous work on other shorter-pulse, less energetic lasers.”
The other LLNL invited talks were:
Physicist Tammy Ma also co-headlined an event held separately from the APS conference. Sponsored by the general-interest science group Science on Tap of Oregon and Washington, the event drew 184 attendees who came to hear Ma talk about the progress of ICF fusion energy research at NIF, the largest and most energetic laser facility ever built.
Arturo Dominguez, science education senior program leader from the Princeton Plasma Physics Lab, joined Ma to talk about the state of magnetic fusion energy research.
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