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

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

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

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

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