Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session NM11: Mini-Conference on Recent Advances in Magnetic Fields in High Energy Density Plasmas ILive
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Chair: Carolyn Kuranz, University of Michigan |
Wednesday, November 11, 2020 9:30AM - 10:00AM Live |
NM11.00001: Magnetically Driven Collisionless Reconnection at Low Plasma Beta Using Novel Laser-Powered Capacitor Coils Invited Speaker: Lan Gao Magnetic reconnection is a fundamental physical process occurring in nearly all magnetized plasmas in nature and in laboratory fusion experiments that rapidly converts magnetic energy to the form of plasma flow, thermal particles, and non-thermal energetic particles. The latter is often an observational signature of magnetic reconnection occurring remotely on the Sun and throughout the Universe. Theoretically, magnetic reconnection has been proposed as an efficient accelerator for charged particles to attain non-thermal energies than any previously proposed or known mechanisms, such as collisionless shocks and plasma turbulence. Over the past four years, our team has been dedicated to developing a robust new platform at sufficiently low plasma betas and measuring conspicuous particle acceleration from magnetically driven collisionless reconnection using strong coil currents powered by high power lasers at the Omega EP and Titan Laser Systems [1-2]. The main target is comprised of two parallel copper plates connected by two circular coils. As the high-power lasers irradiate the back plate an electric potential is built, driving strong currents in both coils and creating a quasi-axisymmetric reconnection geometry between them. This geometry allows better plasma confinement and long reconnection X-line and therefore efficient particle acceleration. Ultrafast proton radiography of the electromagnetic field structure showed a direct signature of reconnection and up to 60 kA of currents in the coils [2]. Plasma parameters were measured using an optical probe, confirming the low plasma beta in the reconnection region. Energetic electrons generated by magnetic reconnection were successfully measured with particle spectrometers. Our most recent work extends the coil current generation up to 100 kA by using the Omega EP IR lasers at a much higher laser intensity, opening up the possibility of studying turbulent reconnection at these laser facilities. This talk provides a comprehensive discussion of our experimental work, quantitative comparisons to Particle-In-Cell simulations, and interpretation in the context of astrophysical observations. This work was supported by the National Laser Users Facility under Grant No. NA0003608, the High-Energy-Density Laboratory Plasma Science under Grant No. DE-SC0020103, and the LaserNetUS initiative at the Jupiter Laser Facility. [1] L. Gao et al., PoP 23, 043106 (2016). [2] A. Chien, L. Gao, et al., PoP 26, 062113 (2019). [Preview Abstract] |
Wednesday, November 11, 2020 10:00AM - 10:25AM Live |
NM11.00002: Implementation of laser-driven capacitor coil targets to magnetize an implosion at OMEGA C McGuffey, M Bailly-Grandvaux, JJ Santos, R Florido, C Walsh, F Suzuki-Vidal, FN Beg, A Calisti, JR Davies, S Ferri, MA Gigosos, JJ Honrubia, RC Mancini, T Nagayama, VT Tikhonchuk We present the design of an experiment using laser-driven capacitor-coil targets (CCTs) at OMEGA. These CCTs, consisting of 2 parallel plates and a wire connector loop, have been demonstrated elsewhere to produce \textgreater 100 T fields over volumes $\gg $mm$^{\mathrm{3}}$. Such fields could be applied to various high energy-density experiments to investigate B field effects. Here, two coils in Helmholtz configuration will be driven by 5 OMEGA beams/coil to produce an estimated seed field of \textasciitilde 50T midway between the coils. To demonstrate their use in an HED target, the CCTs will be placed around a cylindrical implosion of Ar-doped D$_{\mathrm{2}}$ gas driven by 40 OMEGA beams (15 kJ, 1.5ns). The seed B field will be characterized, and Ar K-shell emission will be temporally and spectrally resolved. Our modeling with MHD and radiative calculations predicts the B field can alter the hydrodynamic behavior so much as to be measurable in the Ar spectroscopy. The design and initial results will be shared. [Preview Abstract] |
Wednesday, November 11, 2020 10:25AM - 10:50AM Live |
NM11.00003: Magnetothermal instability resulting from gradients in plasma composition James Sadler, Hui Li, Brian Haines The magnetothermal instability can arise in situations of parallel electron temperature and density gradients, such as in laser ablation fronts. We show that there is a related instability occurring when the gradient of the average ion charge state Z is antiparallel to the electron temperature gradient. The transverse magnetic field arises from the collisional thermal force, not the Biermann term, and grows exponentially with a linearized growth rate on hydrodynamic timescales. An MHD simulation shows that the instability can occur even in pressure equilibrium, such that hydrodynamic motion can be neglected to first order. Gradients in Z are prominent in high energy density plasmas, and often have an opposing temperature gradient due to increased radiative cooling. [Preview Abstract] |
Wednesday, November 11, 2020 10:50AM - 11:15AM Live |
NM11.00004: Time-resolved turbulent dynamo in a laser plasma with order-unity magnetic Prandtl number Archie Bott, Petros Tzeferacos, Laura Chen, Charlotte Palmer, Alexander Schekochihin, Don Lamb, Gianluca Gregori Understanding magnetic-field generation and amplification in turbulent plasma is essential for explaining the presence of magnetic fields in the universe. A theoretical framework attributing these fields to the so-called fluctuation dynamo was recently validated by experiments on laser facilities in low-magnetic Prandtl-number (low-Pm) plasmas. However, the same framework proposes that the fluctuation dynamo should behave quite differently for large Pm, the regime relevant to many astrophysical environments. This talk reports a new experiment which creates a high-Pm plasma dynamo. We provide a time-resolved characterization of the plasma's evolution, measuring temperatures, densities, flow velocities and magnetic fields. The magnetic energy in structures with characteristic scales close to the driving scale of the stochastic motions is found to increase by almost three orders of magnitude from its initial value. It is shown that the growth of these fields occurs exponentially at a rate that is much faster than the turnover rate of the driving-scale stochastic motions. Our results point to the possibility that plasma turbulence produced by strong shears may generate driving-scale fields more efficiently than would be anticipated from MHD simulations of the fluctuation dynamo. [Preview Abstract] |
Wednesday, November 11, 2020 11:15AM - 11:40AM Live |
NM11.00005: Generating and diagnosing turbulence in pulsed-power driven magnetised plasmas Jack Hare, G C Burdiak, S N Bland, T Clayson, J W D Halliday, S Merlini, D R Russell, R A Smith, N Stuart, L G Suttle, E R Tubman, S V Lebedev Turbulence is a ubiquitous phenomena in fluids, which allows velocity fluctuations to cascade down to smaller spatial scales until they are dissipated by viscosity. In a magnetised plasma, these velocity fluctuations also drive fluctuations in the temperature, density and magnetic field, which are an important driver of plasma phenomena throughout the universe. We generate turbulence inside a diverse range of pulsed-power driven plasmas, including a reverse shock formed at a target by an exploding tungsten wire array, and the precursor inside an imploding carbon wire array. We study these plasmas using a fast-framing camera, laser interferometry, shadowgraphy and schlieren imaging, Faraday rotation imaging and multi-point collective Thomson scattering. We have developed new diagnostics for studying turbulent plasmas in unprecedented detail, such as an imaging refractometer, which directly measures the spectrum of deflection angles in a probing laser beam, and multi-angle, multi-point collective Thomson scattering using 48 optical fibres. Finally, we will discuss the new PUFFIN generator, which will be built at MIT, and will sustain turbulent magnetised HED plasmas over microsecond timescales. [Preview Abstract] |
Wednesday, November 11, 2020 11:40AM - 12:05PM Live |
NM11.00006: Studying the Saturation of Turbulent Small-Scale Dynamo Using HED Plasma Plumes Hui Li, Kirk Flippo, Andy Liao, Shengtai Li, Yingchao Lu, Alex Rasmus, Sallee Klein, Codie Kawaguchi, Joseph Levesque, Carolyn Kuranz, Chikang Li We present the latest results from the Omega-EP experiments on demonstrating the small-scale turbulent dynamo, using a cone design (Liao et al. 2019). Using diagnostics including a $4\omega$ laser beamline for angular filter refractometry and a sheath-accelerated proton beamline for deflectometry, we are able to reliably measure the hydrodynamics and magnetic field of the target plasma and observe the turbulent dynamo over a few nanoseconds of activity across two orders of magnitude in spatial scales between tens of micron and $\sim$ mm. Based on these results, we suggest a new type of experiments on NIF where the plasma volume with dynamo action can be larger and much longer lived. This enables the analysis as the small-scale turbulent dynamo reaches its saturation stage. [Preview Abstract] |
Wednesday, November 11, 2020 12:05PM - 12:30PM Live |
NM11.00007: Development of the MagRT Experimental Platform on the NIF M.J.-E. Manuel, S. Nagel, B.B. Pollock, E.G. Carroll, D. Kalantar, K.S. Raman, C. Samulski, B. Srinivasan, Z. Barbeau, B. Albertazzi, G. Rigon, M. Koenig, A. Casner Magnetic fields can play an important role in the evolution of hydrodynamic instabilities in many different physical systems. Of particular interest are the Richtmyer-Meshkov, Rayleigh-Taylor (RT), and Kelvin-Helmholtz instabilities, as all three are relevant to fusion concepts and astrophysical systems, such as the interaction of shock waves with interstellar clouds and in the shells of supernova remnants. This talk will cover progress on the development of an experimental platform on the National Ignition Facility (NIF) to study magnetized hydrodynamic instabilities, with particular interest towards blast-wave-driven RT instabilities. Physics constraints high-lighted by previous experiments performed at Laboratoire pour L'Utilisation des Lasers Intenses (LULI) will be briefly discussed. This material is based upon work supported by the U.S. Department of Energy, Office of Science Financial Assistance Program under Award DE-SC0020055 and the Office of Fusion Energy Sciences High-Energy-Density Laboratory Plasma Science Program under DE-SC0018993. [Preview Abstract] |
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