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The Future of Frontier

Plasma Science

Talk and Chat series 2020

Dr. Arijit Bose (MIT)
October 19th 2020
4PM EST
Webminar available to watch:Exploring the effects of externally imposed B-fields on matter at extreme conditions

Magnetization of matter at extreme conditions broadens the scope for exploratory sciences with laser-produced plasmas. The widespread applications of B-fields include magnetized inertial confinement fusion (ICF), laboratory models of astrophysical phenomenon and characterization of magnetized materials. In this talk, I will discuss a new magnetized shock-driven implosion platform at OMEGA, that uses 50 T externally imposed initial magnetic fields. This platform produces unique plasma conditions, with both strongly magnetized electrons and ions. Conditions for ion magnetization, i.e., ion gyro-radius shorter than the mean free path, or Hall parameter > 1, is particularly challenging to attain in laser-produced plasmas. Furthermore, I will discuss how magnetization can suppress kinetic effects in the hot spot of ICF implosions. This platform opens up opportunities for studies of (ion) Knudsen number reduction and (electron) thermal transport suppression in strongly magnetized high-energy-density plasmas. I will also share my journey through the field of high energy density sciences, from the University of Rochester and the University of Michigan, where I worked on ICF and hydrodynamic instabilities.

Dr. Paul C. Campbell, University of Michigan
September 28th 2020
4pm EDT
Webinar available to watch at: Stabilizing Liner Implosions with Dynamic Screw Pinches

Fast z-pinches are formed when large axial currents run through cylindrical metal shells, or liners, which produces a Lorentz force that implodes the system. This implosion process is susceptible to magnetohydrodynamic instabilities, such as the magneto-Rayleigh-Taylor instability (MRTI). These instabilities are undesirable since many experiments rely on a sufficiently symmetric implosion. The study of MRTI is of particular relevance to magnetized fusion concepts like magnetized liner inertial fusion (MagLIF), which are degraded by this instability. To reduce MRTI growth in solid-metal liner implosions, the use of a dynamic screw pinch (DSP) has been proposed [P. F. Schmit et al., Phys. Rev. Lett. 117, 205001 (2016)]. In a DSP configuration, a helical return-current structure surrounds the liner, resulting in a helical magnetic field that drives the implosion. In this dissertation, the first experimental tests of a solid-metal liner implosion driven by a DSP are presented [P. C. Campbell et al., Phys. Rev. Lett. 125, 035001 (2020)]. Using the 1-MA, 100–200-ns COBRA pulsed-power driver, three DSP cases were tested (with peak axial magnetic fields of 2 T, 14 T, and 20 T) along with a standard z-pinch (SZP) case (with a straight return-current structure and thus zero axial field). These experiments demonstrated enhanced stability in thin-foil liner implosions. When compared to theory [Velikovich et al., Phys. Plasmas 22, 122711 (2015)], these results agree reasonably well. The strongest DSP case tested showed a factor of three reduction in instability amplitude at stagnation. Specifically, at a convergence ratio of 2, the MRTI amplitudes for the SZP case and for the 14-T and 20-T DSP cases were, respectively, 1.1±0.3 mm, 0.7±0.2 mm, and 0.3±0.1 mm. While the convergence ratio of the experiments was low, relative to other imploding liner experiments, the trends in the data were clear; when the DSP generates stronger axial magnetic fields, the instability amplitude decreases. Measurements using micro B-dot probes showed that the return current structures in the DSP cases generated axial magnetic field values in line with the values predicted by electromagnetic simulations. Measurements taken inside the imploding liners showed a significant amount of flux injection and subsequent flux compression. Throughout the short-pulse experiments on COBRA, the 14-T and 20-T DSP cases stagnated 10–40 ns earlier than the SZP cases. Analysis of the stagnation times and current waveforms demonstrated that the small differences in current delivery were not enough to account for the differences in stagnation times. The shorter overall implosion time of the DSP configuration, relative to the SZP configuration, is most likely due to the added magnetic pressure from the axial field that is present in the DSP case. The load current on COBRA was measured with a Rogowski coil in the power feed. After peak current, the Rogowski measurement would often terminate during the falling edge of the current pulse in the SZP experiments, while in the 14-T DSP experiments, it would often continue well after the current pulse had returned to zero. Preliminary particle-in-cell (PIC) simulations suggest that, after peak current, electrons sourced near the liner are directed down into the power feed towards the Rogowski coil in the SZP configuration, while simulations of the 14-T DSP configuration suggest these electrons are ejected radially outward through the gaps between the DSP return-current posts and thus away from the Rogowski coil. The lack of electron interaction with the Rogowski coil may explain why the load current measurements persist for longer in the DSP experiments. This observation could have important implications for power delivery in magnetically driven implosions in general.

Prof. Franklin Dollar, UC Irvine
September 14th 2020
4pm EDT
Webinar available to watch at: Inclusive Excellence in High Energy Density Science

Given the broader conversations taking place nationally on anti-Black racism, it is necessary to take a moment to reflect on the state of inclusive excellence in High Energy Density Science. Physical sciences has poor representation for many populations, including gender, ethnicity and race, or students with disabilities. Physics has some of the lowest representation, and plasma physics consistently ranks among the bottom. After a brief discussion of the state of diversity in the sciences, several techniques will be discussed to broaden participation in research, to improve climate, and to strengthen the community both within research groups and to the broader public.

Dr. Tammy Ma, LLNL
August 17th 2020
4pm EDT
Webinar available to watch at: Future Perspective for High-Intensity Laser HED Science at LLNL

The Advanced Photon Technologies (APT) high-intensity HED science program at LLNL seeks to provide new capability in, and drive forward frontier HED with short-pulse laser science and applications. We will discuss recent work in multi-ps, very high energy short pulse laser experiments on the NIF-ARC laser, as well as work towards a closed-loop paradigm to accelerate scientific discovery, integrating high-repetition-rate laser experiments, machine learning, and physics-based cognitive simulations. Using these novel tools, areas of active research include high-intensity laser interactions with matter, laser-driven secondary sources, plasma optics, future light sources, and the development of high-throughput diagnostics, targetry, modeling, and machine learning.

Dr. Kathleen Weichman, UCSD
August 10th 2020
4pm EDT
Webinar available to watch at: Relativistic laser-plasma interaction with kilotesla applied magnetic fields

Recent advances in magnetic field generation are rapidly enabling new regimes in magnetized high energy density physics. However, relatively little is currently known about the kinetic effects of kilotesla-level magnetic fields in relativistic laser-produced plasma. In this talk, I will discuss a variety of configurations in which applied magnetic fields can fundamentally alter plasma dynamics at or near experimentally relevant field strengths. In this regime, the applied magnetic field is too weak to initially magnetize hot electrons, yet is still capable of delivering new and often surprising effects in areas including ion acceleration and magnetic field generation. These effects become particularly relevant at the kilotesla level, suggesting that experimentally available applied magnetic fields may soon be capable of delivering improvements in applications of relativistically intense short pulse laser-plasma interaction.

Dr. Genia Vogman, LLNL
July 27th 2020
4pm EDT
Webinar available to watch at: Kinetic physics of magnetized plasmas in pulsed power inertial confinement fusion experiments

Pulsed power experiments run mega-amps of current through a load to produce and study high energy density matter. Experimental results show that the formation of low-density plasmas in the power feeds gives rise to parasitic currents, which affect load dynamics and limit load parameters. To understand the inimical transport properties of these low-density, magnetized, collisionless plasmas and how they affect experimental outcomes, the environment within the power feeds is studied using noise-free high-order continuum kinetic simulations, which offer enhanced solution accuracy. The Vlasov simulations, together with new methods for constructing kinetic equilibria, enable the study of isolated physics and show that Kelvin-Helmholtz instabilities are candidate drivers of transport. Detailed comparisons between kinetic and two-fluid simulations also demonstrate how these instabilities and their associated transport properties are modified by the presence diamagnetic drift, charge separation, and finite Lamor radius effects. By enabling detailed exploration of plasmas in which ion gyroradii are comparable to gradient scale lengths, the computational techniques advance the state of the art in kinetic modeling and improve our understanding of pulsed power systems.

Dr. Patrick Knapp, Sandia National Laboratories
July 20th 2020
4pm EDT
Webinar available to watch at: Opportunities in HED physics research on Z: ICF, Data Science, Hydrodynamics, and more

The Z Machine at Sandia National Laboratories hosts a wide variety of experiments studying physics under extreme conditions. In this talk I will highlight various efforts that I am currently taking part in to advance our understanding of ICF, hydrodynamics, and transport physics in support of our Stockpile stewardship mission. We have also recently undertaken an effort to explore the use of modern data science methods in HED physics research in an effort to maximize the knowledge we gain from each experiment as well as our ability to integrate data with theory.

Dr. Félicie Albert, LLNL and Chair of LaserNetUS
June 15th 2020
4pm EDT
Webinar available to watch at: LaserNetUS

In 2018, the DOE Office of Science, Fusion Energy Sciences, established a network of high power laser user facilities, LaserNetUS, to invigorate the US High Energy Density (HED) plasma physics and high field laser community by supporting a new mechanism for scientific discovery and technical innovation. This DOE initiative was a direct response to a 2017 report of the National Academy of Sciences (“Opportunities in Intense Ultrafast Lasers: Reaching for the Brightest Light”) that assessed the physics potential in laser-driven high field science in the US, recommending the creation of a broad national network that includes mid-scale laser infrastructure. After only one and a half years of operation, LaserNetUS has seen great success. In 2019 alone, it has assigned beam time to over 200 user scientists and researchers from dozens of institutions nationwide. An important role fulfilled by LaserNetUS is the training of students and postdocs, who will be the drivers of future scientific discoveries and technological development. Well over 100 students and post-docs from user groups have already participated in LaserNetUS experiments. More information can be found here: LaserNetUS.org.

Prof. Carolyn Kuranz, University of Michigan, Ann Arbor
June 1st 2020
4pm EDT
Webinar available to watch at: A Community Plan for Fusion Energy and Discovery Plasma Sciences

In late 2018, the APS Division of Plasma Physics announced the initiation of a community-based process for the long-range strategic planning for fusion and plasma science in the U.S. Phase I of this process, which involved several community activities, concluded in March 2020 with a final report, "A Community Plan for Fusion Energy and Discovery Plasma Sciences" delivered to the Fusion Energy Sciences Advisory Committee. This provides the basis for a decade-long comprehensive consensus plan to deliver fusion energy and advance plasma science. This talk will provide an overview of the year-long Phase I process and a summary of the key opportunities for Discovery Plasma Science in three areas: Explore the Frontiers of Plasma Science, Understand the Plasma Universe, and Create Transformative Technologies. Our vision is to realize the potential of plasma science to deepen our understanding of nature and to provide the scientific underpinning for plasma-based technologies that benefit society by developing a fundamental understanding of the unique dynamical behaviors of plasmas and identify opportunities where the unique properties of plasmas can be used to engineer technologies that support a growing and sustainable economy. In order to establish and maintain the U.S. leadership in plasma science, we require world class facilities and reproducible theory, computation, and measurements. More information on the Community Planning Process and the Final Phase I report can be found here: DPP CPP.

2020 Talk and Chat Series

The Future of Frontier

Plasma Science

Talk and Chat series 2020

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