Bulletin of the American Physical Society
60th Annual Meeting of the APS Division of Plasma Physics
Volume 63, Number 11
Monday–Friday, November 5–9, 2018; Portland, Oregon
Session TO6: Laser-Plasma and Beam-Plasma Interactions in HED systems |
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Chair: Michael Rosenberg, University of Rochester Room: OCC B115-116 |
Thursday, November 8, 2018 9:30AM - 9:42AM |
TO6.00001: Combination of Up to 21 Frequency Shifted Beams with a Plasma Optic Robert Kirkwood, Patrick Poole, Thomas D Chapman, Scott Wilks, W. Dunlop, B. J. Macgowan, K. Fournier, B. E. Blue, B. M. Van Wonterghem A plasma-based optic is demonstrated that combines the energy and fluence of up to 21, 1.1 kJ, frequency shifted laser beams into a single beam, producing an output of up to 7.7 +- 1.7 kJ in a 1ns pulse. The technique uses Cross Beam Energy Transfer (CBET) and builds on previous work to make beams with energy and fluence beyond that otherwise available at NIF [1]. The self-generated plasma diffractive optic used is far more damage resistant, and inherently capable of producing much higher single beam fluence and radiance than solid state optics. Such beams are needed for applications, including potentially pumping a second stage of plasma amplification and compression at multi-ps time scales. The results also aid the validation of models of CBET [2] which predict a larger number of non-resonant pump beams will scale up outputs still further. [1] R. K. Kirkwood et al Nat. Phys. 14 , 80 (2018). [2] R. K. Kirkwood et al Phys. of Plas. 25 056701 (2018). |
Thursday, November 8, 2018 9:42AM - 9:54AM |
TO6.00002: Anisotropic heating and magnetic field generation due to Raman scattering in laser-plasma interaction Thales Silva, Jorge Vieira, Masahiro Hoshino, Ricardo Fonseca, Luis O Silva The interaction of intense electromagnetic waves with plasmas is a rich research topic. Magnetic fields play a crucial role in this context and there are several processes that can lead to the generation and amplification of these fields. Recent experiments, for instance, demonstrated the generation of large-scale magnetic fields due to hot electron currents in underdense plasmas and determined the turbulent dynamics of intense magnetic fields in laser-solid interactions. |
Thursday, November 8, 2018 9:54AM - 10:06AM |
TO6.00003: Magnetic field calculation from the Thomson scattering spectra in Weibel unstable counter-streaming plasmas Colin Bruulsema, Frederico Fiuza, Wojciech Rozmus, George F Swadling, Paulo Alves, Siegfried Glenzer Thomson Scattering (TS) is a powerful diagnostic for evaluating the properties of high-energy-density plasmas. We analyze TS cross-sections and dynamical form factors from electron density fluctuations and from distribution functions in particle-in-cell (PIC) simulations of Weibel unstable counter steaming plasma relevant to astrophysical collionsionless shocks. These form factors are compared with analytical theory results and experimental measurements.
We demonstrate for the first time the capability to calculate local magnetic field gradients from beam modes in TS spectra from quasi stationary plasma corresponding to a saturated state of the Weibel instability. This method is compared to the magnetic fields present in PIC simulations. We also show that the temporal evolution of the TS spectra can provide some information about the non-linear stage of the instability. These techniques are applied to TS Spectra from recent experiments at the Omega facility to estimate the magnetic field strength generated. |
Thursday, November 8, 2018 10:06AM - 10:18AM |
TO6.00004: Investigating Weibel instability growth in laser-driven interpenetrating flows using optical Thomson Scattering George Swadling, Drew P Higginson, Channing M Huntington, Dmitri D Ryutov, Scott Wilks, Hye-Sook Park, Frederico Fiuza, Wojciech Rozmus, Colin Bruulsema, James Ross Collisions of high Mach number flows are ubiquitous in astrophysics. Because of the low density of astrophysical plasmas, collisional mean free paths are typically large and therefore observed shock waves must be "collisionless", i.e. due to a localization of ions by self-generated electro-magnetic fields. Experiments conducted using high power lasers (NIF, OMEGA), producing counter-streaming, high-velocity plasma flows via laser ablation (1016Wcm-2) of solid targets, aim to answer questions relevent to collisionless shock physics: the importance of electromagnetic-filamentation (Weibel) instabilities in shock formation, the self-generation of B-fields in shocks, the influence of external B-fields on shock formation, and the signatures of particle acceleration in shocks. New Thomson scattering measurements provide direct evidence of the development of Weibel filaments. Modulations in the intensity of the ion-feature peaks corresponding to the two interpenetrating ion streams provide a measurement of modulations in the ion current, while modulations in the electron feature indicate the development of a strong transverse modulation in the density of the plasma, consistent with the nonlinear growth phase of the Weibel instability. |
Thursday, November 8, 2018 10:18AM - 10:30AM |
TO6.00005: Investigation on kinetic effects of relativistic flow transport in ambient plasma environment Bin Qiao, W. P. Yao, Z. H. Zhao, Z. Lei Relativistic flows (RFs) are particularly intriguing phenomena ubiquitously existed in the Universe and are often connected with exciting high-energy astrophysical central engines. After a century since their first discovery, many efforts have been made to investigate the launch and propagation of RFs in macroscopic scales. However, there are still many open questions regarding to the fundamental parameters of RFs and the ambient environment, and how they interact with each other. In this talk, I shall report recent progress on the theoretical and numerical studies of RFs transport in ambient environment, using fully kinetic Particle-in-Cell (PIC) simulations. For RFs in AGNs where the composition remains unclear, we find that the baryon component, so-called baryon loading effect (BLE), can elongate their transport distance and alter their electron phase space distribution [1]. For RFs in XRBs where extreme magnetic fields exist, we find that quantum electrodynamic (QED) effects play a crucial role, enabling a particle-photon-particle relay transport mechanism [2]. These prove that the microscopic dynamics of can significantly determine the macroscopic transport of RFs. [1] W. P. Yao, B. Qiao et al., NJP 20, 052060 (2018). [2] W. P. Yao, B. Qiao et al., PoP 24, 082904 (2017). |
Thursday, November 8, 2018 10:30AM - 10:42AM |
TO6.00006: Magnetic field generation in plasma waves driven by co-propagating intense twisted lasers Yin Shi, Jorge M Vieira, Raoul M Trines, Robert Bingham, Baifei Shen, Robert J Kingham We present a new magnetic field generation mechanism in underdense plasmas driven by the beating of two, co-propagating, Laguerre-Gaussian (LG) orbital angular momentum (OAM) laser pulses with different frequencies and also different twist indices. Results of 3D particle-in-cell simulations show that the twisted ponderomotive force drives up an electron plasma wave with a helical rotating structure. For the case of 300 fs duration, 3.8×1017 W/cm2 peak laser intensity we observe magnetic field of up to 0.4 MG. We will also outline a theoretical model, based on cold electron fluid equations, that reproduces that pertinent features of the PIC simulations – including the axial magnetic field – in the appropriate limits and elucidates the mechanism and highlights its scaling with key parameters.To second order, there is a nonlinear rotating current leading to the onset of an intense, static axial magnetic field, which persists over a long time in the plasma (ps scale) after the laser pulses have passed by. Applications of this new method of magnetic field creation will be discussed. |
Thursday, November 8, 2018 10:42AM - 10:54AM |
TO6.00007: Studying Magnetospheric Collisionless Beam Instabilities and ULF Waves in the Laboratory Peter Ver Bryck Heuer, Martin S. Weidl, Robert S Dorst, Derek Schaeffer, Carmen G Constantin, Stephen T Vincena, Shreekrishna Tripathi, Walter N Gekelman, Dan Winske, David Jeffrey Larson, Christoph Niemann Collisionless ion-ion beam instabilities parallel to the background interplanetary magnetic field are an important feature of planetary bow shocks, driving ultra-low frequency (ULF) waves that partially determine the ion velocity distribution in the parallel foreshock. However, the growth and saturation phases of these instabilities are difficult to study in situ. A recent series of parameter-scaled experiments at the University of California, Los Angeles aims to supplement spacecraft data by observing the growth of one such instability, the Right-Hand Resonant Instability (or RHI), in the laboratory. The instability is driven by a super-Alfvénic “beam” of laser-produced plasma expanding parallel to a background magnetic field over 80 ion inertial lengths through the large, magnetized ambient plasma of the Large Plasma Device (LAPD). Dimensionless parameters are comparable to the terrestrial magnetosphere. Measurements of the magnetic field with an array of 3-axis magnetic flux “bdot” probes show waves with dimensionless spectral properties similar to ULF waves observed in the terrestrial foreshock, consistent with excitation of the RHI. Measurements are also compared to hybrid simulations of parallel shock formation. |
Thursday, November 8, 2018 10:54AM - 11:06AM |
TO6.00008: Generating near solid density reacting ion distributions using intense short pulse lasers. Gary Grim, Andreas J Kemp, Scott Wilks, Edward P Hartouni, Shaun Kerr Simulations and recent experimental results of a new platform for generating near solid density reacting ion distributions using intense short pulse lasers will be presented. The platform consists of a thin unstructured CH or CD foam with O(100) nm scale pores and ligaments mounted on a thin solid density CH support. The solid CH is illuminated by an intense, ~5 x 1019 W/cm2, short pulse, ~40 fs, laser having an ASE component less than 10-8 of the main pulse. The recirculating hot electrons generated at the pre-plasma critical surface induce electric fields within the foam structure causing TNSA acceleration of the foam ions into the voids. This results in a near solid density charged ion distribution with kinetic energies approaching 200 keV. These energies and densities are sufficient to produce measurable quantities of charged particle reactions, such as, 12C(p,γ)13N, allowing for the study of cross sections with astrophysical relevance, as well as for direct studies of screening effects in charged particle reactions occurring in hot plasma like conditions. |
Thursday, November 8, 2018 11:06AM - 11:18AM |
TO6.00009: Observation of Weibel-like radial filamentation from time resolved dynamics of a kHz relativistic laser interaction with a sub-micron transparent sheet John T Morrison, Gregory K. Ngirmang, Scott B Feister, Kevin M George, Adam J Klim, Joseph C Snyder, Joseph R Smith, Kyle Frische, Chris M Orban, Enam A Chowdhury, William M Roquemore A significant amount of work has been done on relativistic electron dynamics where results are inferred from emitted particles and various probes parallel to the target surface. In this work a free standing sub-micron transparent liquid sheet target is exploited to produce shadowgraphic movies of the transverse expansion of the relativistic electrons with 100 fs resolution. The ionization front expansion rate, extent, and duration are observable in addition to the subsequent hydrodynamic evolution of the target. Particle-in-cell (PIC) simulations indicate Weibel instability generated radial current filaments corroborated by features observed in the shadowgraphy. |
Thursday, November 8, 2018 11:18AM - 11:30AM |
TO6.00010: Tera-FLOP particle-in-cell simulations of rapid ionization front expansion on a target due to a short-pulse ultra intense laser Gregory Ngirmang, John T Morrison, Scott B Feister, Kevin M George, Adam J Klim, Joseph C Snyder, Joseph R Smith, Kyle Frische, Chris Orban, Enam A Chowdhury, William M Roquemore Recent experiments utilizing a novel shadowgraphy diagnostic have allowed for time resolved measurements on a sub-picosecond time scale of the ionization of a sub micron thick target after irradiation by an intense (5×1018 W/cm2) short-pulse laser. The shadowgraphs show filaments in the ionization, suggesting that Weibel-like instabilities play a role in ionization dynamics once the laser has interacted with the target. In order to model this experiment, fully three dimensional particle-in-cell simulations, with high spatial resolution (50nm to 10nm cells) over a relatively large section of the target (40 microns by 40 microns) were required. Simulations using the Large-Scale Plasma code were performed which pushed the code's limits, requiring processing of terabytes of data and concurrent computation in the regime of a hundred trillion of floating point operations per second (Tera-FLOP). These simulations demonstrate filamentation of the magnetic field in the target yielding a density pattern consistent with the experimental observation, and this instability is seeded while the laser is still interacting with the target. |
Thursday, November 8, 2018 11:30AM - 11:42AM |
TO6.00011: Particle-in-Cell Simulations of Density Peak Formation and Ion Acceleration from Ultrashort Pulse Laser-Driven Ponderomotive Steepening Joseph R. Smith, Chris M. Orban, Gregory K. Ngirmang, John T. Morrison, Enam A. Chowdhury, William M. Roquemore We use particle-in-cell (PIC) simulations and simple analytic models to investigate the laser plasma interaction known as ponderomotive steepening. When laser light reflects at the critical density of a plasma, it is well known that the resulting standing electromagnetic wave will modify the electron density profile via the ponderomotive force, which creates peaks in the electron density separated by approximately half of the laser’s wavelength. What is less well studied is that this charge imbalance accelerates ions towards the electron density peaks, modifying the density profile of the plasma. Idealized PIC simulations with an extended under-dense plasma are used to isolate the dynamics of ion density peak growth, and exhibit counter-steaming populations of keV-scale ions. We identify an ‘ultrashort pulse laser regime,’ where the timescale for the resultant standing electromagnetic wave is shorter than the timescale for ions to reach an electron peak and equilibrate. We discuss conditions under which this phenomenon could be observed and how ion energy may depend on factors such as the laser’s wavelength, pulse duration, and intensity. |
(Author Not Attending)
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TO6.00012: Development of Micromachined G-band Energy-Recirculating Folded Waveguide Traveling-Wave Tube Oscillator Ingeun Lee, Ashwini Sawant, Wonjin Choi, Jinwoo Shin, EunMi Choi We present development results of an energy-recirculating folded waveguide traveling-wave tube oscillator internally driven by a backward-wave oscillator (BWO). The BWO, as a driving source, converts the beam energy achieved from electrostatic energy to electromagnetic energy. The generated radio frequency signal in the BWO is amplified in the traveling-wave tube using the spent electron beam as an energy-recirculating method. We exhibit a detailed design process and analysis of the individual circuits, as well as those of the combined circuit, which are simulated using the CST Particle Studio and MAGIC code. A maximum average output power of 43.55 W at a frequency of 272.2 GHz is obtained in simulation under a consideration of ohmic loss with conductivity 5.51 × 107 S/m. The experimental results will be presented and compared to the simulation result. A nanocomputer numerical control (nano-CNC) machining technique was used for manufacturing FWGs. Manufactured FWGs operating in the G- (110–300 GHz) and Y-bands (325–500 GHz) demonstrated the highest reported root mean square surface roughness less than 21 nm in the Y-band. Detailed fabrication process and results of the FWGs using nano-CNC machining will be presented in detail. |
(Author Not Attending)
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TO6.00013: Design and Operation of a Second Harmonic Dual Mode Gyrotron for OAM Beam Generation Ashwini Sawant, Mun Seok Choe, Ingeun Lee, EunMi Choi A novel scheme of Orbital angular momentum (OAM) beam generation in radio frequency (RF) range using Gyrotron is demonstrated. The Gyrotron generates few kilowatts (~30-40 kW) of power at 190 GHz frequency in a second harmonic mode-pair TE8,3/TE11,2 from 32/37 kV, 7A electron beam. Switching between the operating modes is achieved by changing the cathode voltage at constant magnetic field. It incorporates the two sinusoidal perturbations in the cylindrical cavity to eliminate the fundamental mode competition. This mode-pair is propagated in free space in the form of OAM beams having the order of l = 8/11 same as the azimuthal mode index. These high-power OAM beams can be used for free space RF communication and RF beam plasma interaction. These waveguide modes have been further radiated from an overmoded waveguide section into free space to reduce its divergence which increases the propagation distance of these OAM RF beams. This technique of natural generation of high-power OAM RF beams opens a wide research area for study of the OAM communication and plasma interaction with vortex RF beams. |
Thursday, November 8, 2018 12:06PM - 12:18PM |
TO6.00014: Recent progress on the harmonic recirculating planar magnetron Drew Packard, Geoffrey B Greening, Nicholas M Jordan, Steven C Exelby, Patrick Y Wong, Yue-Ying Lau, Ronald Matthew Gilgenbach, Brad Hoff, Jason Hammond The Multi-Frequency Recirculating Planar Magnetron (MFRPM) [1,2] is a novel high power microwave source capable of generating multiple frequencies simultaneously at multi-MW power levels. Output frequencies were near 1 and 2 GHz, generated by an L-Band Oscillator (LBO) and an S-Band Oscillator (SBO), respectively. The MFRPM is the first dual-frequency HPM magnetron to demonstrate harmonic frequency locking, where the SBO operating frequency locks to the LBO’s harmonic. To study this locking phenomenon, the Harmonic Recirculating Planar Magnetron (HRPM) has been designed. The completed design will be presented, along with relevant simulation results, and preliminary experimental results. The HRPM will be driven by MELBA-C, which applies -300 kV, 1-5 kA for 0.3-1.0 μs. [1] Greening, Ph.D Dissertation, “Multi-Frequency Recirculating Planar Magnetrons,” University of Michigan, 2017, [2] Greening et al, “Harmonic Frequency Locking in the Multi-Frequency Recirculating Planar Magnetron”, IEEE T-ED, vol. 65, 2347, (2018). |
Thursday, November 8, 2018 12:18PM - 12:30PM |
TO6.00015: Neutral Beam Injection system with tunable beam energy for the C-2W experiment S. Korepanov, P. Deichuli, N. Deichuli, N. Stupishin, K. Pirogov, M. Slepchenkov, V. Kapitonov, A. Ivanov, A. Dunaevsky, and the TAE team Reproducible beam-driven Field-Reversed Configurations (FRCs), sustained by tangential neutral beam injection for times significantly longer than characteristic plasma decay times, have been demonstrated with steady magnetic fields in the C-2U experiment [1]. In order to demonstrate FRC ramp-up, the C-2W experimental device has been designed, built and commissioned. It is equipped with a set of eight neutral beam injectors (NBI’s). Four out of the eight NBIs have a capability whereby the beam energy can be tuned during a shot from the initial 15 keV up to 40 keV at a constant beam current. Tunable beam energy allows optimization of the beam-plasma coupling during ramp-up of the magnetic field in the confinement section. This presentation provides an overview of the NBI system with tunable beam energy, including its design, layout of the power supply system, and initial operation results. [1] M.W. Binderbauer et al., AIP Conf. Proc. 1721, 030003 (2016) |
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