Computer simulation has revolutionized the way everything is designed, including particle accelerators. Through advanced simulation, one can optimize performance in a complicated parameter space, identify and avoid potential problems, and even make new discoveries. Berkeley Lab has an ideal combination of resources for this challenging task, with the subject-matter expertise of our Accelerator Modeling Program and its network of collaborators, together with the algorithmic and coding expertise of the Computing Sciences Area and the processing power of NERSC, as exemplified by this issue’s science highlight.
ATAP also recently organized and hosted the inaugural Workshop on Instrumentation and Diagnostics for Superconducting Magnets (IDSM01), bringing together some 35 of the world’s leading experts on this key aspect of designing and building the magnets of tomorrow’s accelerators. Superconducting magnets have historically been a strength of ATAP and our Engineering Division partners in the Berkeley Center for Magnet Technology. We are pleased and honored by the magnet community’s response to this opportunity; together we can push forward to the next generation of more powerful, reliable, and cost-effective magnets, to the benefit of all.
Outreach to the next generation of STEM professionals and informed citizens is another ATAP priority. The annual Nuclear Science Day for Scouts, as well as Daughters and Sons to Work Day, recently brought many young people to Berkeley Lab to get to know what we do. Two more opportunities to get involved are coming up soon through the Oakland Unified School District: Science Fair, where Berkeley Lab has an ever-popular booth, and the Dinner with a Scientist event.
All that we do, we are committed to doing safely and with respect for the environment. In that spirit, we held our annual Safety Day, joined by two organizations with close ties to ATAP: the Engineering Division and the ALS-Upgrade Project. We are tracking longer-term action items to completion as we accelerate into another year of science with all the benefits of tidy and organized workspaces.
A BREAKTHROUGH IN COMPUTATIONAL STUDY OF LASER-PLASMA INTERACTIONS
—New simulation tool brings advanced scalability to ultra-high-intensity physics simulations
From an article by Kathy Kincade, Berkeley Lab Computing Sciences
A new 3D particle-in-cell (PIC) simulation tool developed by researchers from Lawrence Berkeley National Laboratory and CEA Saclay is enabling cutting-edge simulations of laser/plasma coupling mechanisms that were previously out of reach of standard PIC codes used in plasma research. More detailed understanding of these mechanisms is critical to the development of ultra-compact particle accelerators and light sources that could solve long-standing challenges in medicine, industry, and fundamental science more efficiently and cost-effectively.
In laser-plasma experiments such as those at the Berkeley Lab Laser Accelerator (BELLA) Center and at CEA Saclay — an international research facility in France that is part of the French Atomic Energy Commission — very large electric fields within plasmas accelerate particle beams to high energies over much shorter distances when compared to existing accelerator technologies. Supercomputer simulations have become increasingly critical to this research, and Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC) has become an important resource in this effort.
The long-term goal of these laser-plasma accelerators (LPAs) is to one day build colliders for high-energy research, but many spinoffs are being developed already. For instance, LPAs can quickly deposit large amounts of energy into solid materials, creating dense plasmas and subjecting this matter to extreme temperatures and pressure. They also hold the potential for driving free-electron lasers that generate light pulses lasting just attoseconds. Such extremely short pulses could enable researchers to observe the interactions of molecules, atoms, and even subatomic particles on extremely short timescales.
Supercomputer simulations have become increasingly critical to this research, and Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC) has become an important resource in this effort. By giving researchers access to physical observables such as particle orbits and radiated fields that are hard to get in experiments at extremely small time and length scales, PIC simulations have played a major role in understanding, modeling, and guiding high-intensity physics experiments. But a lack of PIC codes that have enough computational accuracy to model laser-matter interaction at ultra-high intensities has hindered the development of novel particle and light sources produced by this interaction.
This challenge led the Berkeley Lab/CEA Saclay team to develop their new simulation tool, dubbed Warp+PXR, an effort started during the first round of the NERSC Exascale Science Applications Program (NESAP). The code combines the widely used 3D PIC code Warp with the high-performance library PICSAR co-developed by Berkeley Lab and CEA Saclay. It also leverages a new type of massively parallel pseudo-spectral solver co-developed by Berkeley Lab and CEA Saclay that dramatically improves the accuracy of the simulations compared to the solvers typically used in plasma research.
In fact, without this new, highly scalable solver, “the simulations we are now doing would not be possible,” said Jean-Luc Vay, a senior physicist at Berkeley Lab who heads the Accelerator Modeling Program in the Lab’s Applied Physics and Accelerator Technologies Division. “As our team showed in a previous study, this new FFT spectral solver enables much higher precision than can be done with finite difference time domain (FDTD) solvers, so we were able to reach some parameter spaces that would not have been accessible with standard FDTD solvers.” This new solver is also at the heart of the next-generation PIC algorithm with adaptive mesh refinement that Vay and colleagues are developing in the new Warp-X code as part of the U.S. Department of Energy’s Exascale Computing Project.
2D and 3D Simulations Both Critical
Vay is also co-author on a paper published March 21 in Physical Review X that reports on the first comprehensive study of the laser-plasma coupling mechanisms using Warp+PXR. That study combined state-of-the-art experimental measurements conducted on the UHI100 laser facility at CEA Saclay with cutting-edge 2D and 3D simulations run on the Cori supercomputer at NERSC and the Mira and Theta systems at the Argonne Leadership Computing Facility at Argonne National Laboratory. These simulations enabled the team to better understand the coupling mechanisms between the ultra-intense laser light and the dense plasma it created, providing new insights into how to optimize ultra-compact particle and light sources. Benchmarks with Warp+PXR showed that the code is scalable on up to 400,000 cores on Cori and 800,000 cores on Mira and can speed up the time to solution by as much as three orders of magnitude on problems related to ultra-high-intensity physics experiments.
“We cannot consistently repeat or reproduce what happened in the experiment with 2D simulations – we need 3D for this,” said co-author Henri Vincenti, a scientist in the high-intensity physics group at CEA Saclay. Vincenti led the theoretical/simulation work for the new study and was a Marie Curie postdoctoral fellow at Berkeley Lab in Vay’s group, where he first started working on the new code and solver. “The 3D simulations were also really important to be able to benchmark the accuracy brought by the new code against experiments.”
For the experiment outlined in the Physical Review X paper, the CEA Saclay researchers used a high-power (100TW) femtosecond laser beam at CEA’s UHI100 facility focused on a silica target to create a dense plasma. In addition, two diagnostics – a Lanex scintillating screen and an extreme-ultraviolet spectrometer– were applied to study the laser-plasma interaction during the experiment. The diagnostic tools presented additional challenges when it came to studying time and length scales while the experiment was running, again making the simulations critical to the researchers’ findings.
“Often in this kind of experiment you cannot access the time and length scales involved, especially because in the experiments you have a very intense laser field on your target, so you can’t put any diagnostic close to the target,” said Fabien Quéré, a research scientist who leads the experimental program at CEA and is a co-author of the PRX paper. “In this sort of experiment we are looking at things emitted by the target that is far away – 10, 20 cm – and happening in real time, essentially, while the physics are on the micron or submicron scale and subfemtosecond scale in time. So we need the simulations to decipher what is going on in the experiment.”
“The first-principles simulations we used for this research gave us access to the complex dynamics of the laser field interaction, with the solid target at the level of detail of individual particle orbits, allowing us to better understand what was happening in the experiment,” Vincenti added.
These very large simulations with an ultrahigh precision spectral FFT solver were possible thanks to a paradigm shift introduced in 2013 by Vay and collaborators. In a study published in the Journal of Computational Physics, they observed that, when solving the time-dependent Maxwell’s equations, the standard FFT parallelization method (which is global and requires communications between processors across the entire simulation domain) could be replaced with a domain decomposition with local FFTs and communications limited to neighboring processors. In addition to enabling much more favorable strong and weak scaling across a large number of computer nodes, the new method is also more energy efficient because it reduces communications.
“With standard FFT algorithms you need to do communications across the entire machine,” Vay said. “But the new spectral FFT solver enables savings in both computer time and energy, which is a big deal for the new supercomputing architectures being introduced.”
Other members of the team involved in the latest study and co-authors on the new PRX paper include: Maxence Thévenet, a post-doctoral researcher whose input was also important in helping to explain the experiment’s findings; Guillaume Blaclard, a Berkeley Lab affiliate who is working on his Ph.D. at CEA Saclay and performed many of the simulations that were reported in this work; Pr. Guy Bonnaud, a CEA senior scientist whose input was important in the understanding of simulation results; and CEA scientists Ludovic Chopineau, Adrien Leblanc, Adrien Denoeud, and Philippe Martin who designed and performed the very challenging experiment on UHI100 under the supervision of Fabien Quéré.
WHAT GOES ON INSIDE A SUPERCONDUCTING MAGNET? ATAP HOSTS WORKSHOP ON FINDING OUT
A superconducting accelerator magnet is a heavily constructed and tightly encased thing, figuratively and literally opaque, but internal details matter a great deal. As physicists and engineers strive to push both the performance and the cost-effectiveness of these magnets beyond the present state of the art, they are finding ingenious ways to do things like identifying and locating the precursors of a “quench” (sudden local loss of superconductivity) and minimizing the “training” or break-in process. A broad effort in developing novel techniques for magnet diagnostics is geared towards solving long-standing problems such as training, determining quench origins, and identifying quench-driving factors.
Some 35 leading experts in the field, representing 4 US national laboratories and other research institutions, three of their international counterparts, two universities, and a private-sector developer of superconductor, came to Berkeley Lab April 24-26 for the first Workshop on Instrumentation and Diagnostics for Superconducting Magnets (IDSM01). The workshop was aimed at defining a common strategy for diagnostics and establishing a platform for exchanging and circulating new ideas. The results of this ongoing dialogue are expected to benefit not only accelerator-based efforts in high energy and nuclear physics, but other uses of superconducting magnets as well, including the quest to harness fusion energy.
OUTREACH AND EDUCATION
Make a Difference in a Future Colleague’s Life
For an investment of just one or two evenings, you can help the Oakland Unified School District make a difference in STEM education by volunteering for the district-wide Science Fair or their Dinner with a Scientist event.
OUSD Science Fair, 6-8 pm Wednesday, May 8
ATAP’s Outreach and Education Coordinator Ina Reichel invites you to join her at the Berkeley Lab booth. You’ll help with activities that center around the electromagnetic spectrum, giving students a chance to practice making and describing observations (which is second nature to us but an important supplement to classroom activities in a budding scientist’s education). You’ll also get a chance to visit your future colleagues’ science projects. It only takes five minutes of on-the-job training to lead these hands-on activities. If you would like to join in the fun, please contact Ina (x4341, IReichel@lbl.gov).
Dinner with a Scientist: 5-8 pm Monday, May 20 or Tuesday, May 21
An OUSD tradition since 2009, Dinner with a Scientist brings teachers and students together with researchers, university professors, engineers, doctors, veterinarians, and even forensic scientists. You’ll talk about your work, lead an activity, and answer questions, switching tables every 30 minutes (with enough time for you to enjoy your free dinner). The district will host two Dinner with a Scientist events this year: May 20 and 21. Both events run 5-8 p.m. at Chabot Space & Science Center. To learn more or sign up, visit the OUSD Science Events website.
Nuclear Science Day for Scouts
In a Berkeley Lab outreach tradition now in its ninth year, the Nuclear Science Division hosted a Nuclear Science Day for Scouts in Saturday, March 30. Some 180 Scouts from across California (one troop came all the way from Irvine) visited the Lab to learn about nuclear science (including related career possibilities) to fulfill one of the requirements for a merit badge.
Particle accelerators, with their ongoing rich heritage of contributions to our knowledge of the atom, nucleus, and subatomic particles, are regarded as nuclear facilities for merit-badge purposes, and the Advanced Light Source was the focus of many of their experiences. Among the things they learned about were ALS-U, an upcoming major upgrade of the Advanced Light Source; ATAP plays key roles in this transformative reworking of a flagship user facility.
Nuclear Science Day for Scouts would not be possible without numerous volunteers from across the Lab. ATAP staff members Qing Ji and Pat Thomas chaperoned groups of 30 scouts from activity to activity, Warren Byrne led two ALS tours, while Ina Reichel coordinated the ALS tours and directed traffic in the ALS lobby all day. Former ATAP staffers Jose Alonso and Tony Young, still active in retirement and now affiliated with the Physics Division and the ALS, respectively, were also among the 55 people who did a good turn that day by reaching out to the scientists of tomorrow.
Stay in the Know with “Elements,” Berkeley Lab’s New Communication Platform
With nearly 4000 employees and one of the most diverse R&D portfolios anywhere, keeping up with Berkeley Lab can take some doing. Elements, the Lab’s new communication platform, makes it easier by letting you tailor your news feed to your interests, receive urgent communications on your mobile devices, and interact rather than just read. Whatever topics matter most to you, from accelerators to zero-emissions commuting options, find out what’s important by signing up for Elements.
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Berkeley Lab Research Slam: Application Deadline May 31
Early-career scientists and postdocs are invited to participate in the Berkeley Lab Research Slam. Modeled after poetry and storytelling “slams” (and the research-focused UC-Berkeley Grad Slam), the competition gives you three minutes to convey what’s exciting and important about your work. It’s more than just fun — engaging and efficient public speaking about your work is a skill that will pay dividends throughout your career (imagine an “elevator speech” to a prospective sponsor, for instance). And speaking of funding, the winner takes home $3,000, with runner-up and People’s Choice awards as well.
Those who are in an active appointment through October 2019 and received their PhD between January 2012 and December 2018 are eligible. To learn more and get started, visit the Berkeley Lab Research Slam website. The deadline for registering to participate is May 31, followed by a deadline for a short video that will be used to pick the 12 finalists. September 19 is the big day!
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SAFETY: THE BOTTOM LINE
ATAP and Engineering Safety Day Was a Sweeping Success
On Thursday, March 28, 2019, the ATAP and Engineering Divisions and the ALS-U project held their annual Safety Day, performing cleanup and taking care of problems that could be settled immediately within our capabilities. During the cleanup and the subsequent QUEST assessments and management walkthroughs, action items that required more time and resources or professional skills were tabulated.
With 17 QUEST teams and 12 management-walk around teams reporting in thus far, we have identified 226 action items, which will be formally tracked to resolution. The most common were seismic (77), electrical (26), and signage (21).
The cleanup generated approximately
14 bins of e-waste
11 bins of paper and cardboard
4 bins of scrap metal
4 machine carts, 1 pallet, and 1 bin of surplus equipment
3 bins of trash
5 chairs, 1 desk, 1 refrigerator, 1 microwave, and 1 space heater
and the best statistic of all — a testament to staying within our training and physical capabilities and using appropriate personal protective equipment:
Watch the next issue of this newsletter or visit the Safety Day 2019 page on the ATAP website for big news still to come: honors for individual and QUEST-team excellence on Safety Day.