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Journal articles on the topic 'HPC plasma turbulence simulations'

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Published: 8 June 2024

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1

Bouzat, Nicolas, Camilla Bressan, Virginie Grandgirard, Guillaume Latu, and Michel Mehrenberger. "Targeting Realistic Geometry in Tokamak Code Gysela." ESAIM: Proceedings and Surveys 63 (2018): 179–207. http://dx.doi.org/10.1051/proc/201863179.

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In magnetically confined plasmas used in Tokamak, turbulence is respon-sible for specific transport that limits the performance of this kind of reactors. Gyroki-netic simulations are able to capture ion and electron turbulence that give rise to heat losses, but require also state-of-the-art HPC techniques to handle computation costs. Such simulations are a major tool to establish good operating regime in Tokamak such as ITER, which is currently being built. Some of the key issues to address more re- alistic gyrokinetic simulations are: efficient and robust numerical schemes, accurate geometric description, good parallelization algorithms. The framework of this work is the Semi-Lagrangian setting for solving the gyrokinetic Vlasov equation and the Gy-sela code. In this paper, a new variant for the interpolation method is proposed that can handle the mesh singularity in the poloidal plane at r = 0 (polar system is used for the moment in Gysela). A non-uniform meshing of the poloidal plane is proposed instead of uniform one in order to save memory and computations. The interpolation method, the gyroaverage operator, and the Poisson solver are revised in order to cope with non-uniform meshes. A mapping that establish a bijection from polar coordinates to more realistic plasma shape is used to improve realism. Convergence studies are provided to establish the validity and robustness of our new approach.

2

Veltri, P., G. Nigro, F. Malara, V. Carbone, and A. Mangeney. "Intermittency in MHD turbulence and coronal nanoflares modelling." Nonlinear Processes in Geophysics 12, no. 2 (February 9, 2005): 245–55. http://dx.doi.org/10.5194/npg-12-245-2005.

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Abstract. High resolution numerical simulations, solar wind data analysis, and measurements at the edges of laboratory plasma devices have allowed for a huge progress in our understanding of MHD turbulence. The high resolution of solar wind measurements has allowed to characterize the intermittency observed at small scales. We are now able to set up a consistent and convincing view of the main properties of MHD turbulence, which in turn constitutes an extremely efficient tool in understanding the behaviour of turbulent plasmas, like those in solar corona, where in situ observations are not available. Using this knowledge a model to describe injection, due to foot-point motions, storage and dissipation of MHD turbulence in coronal loops, is built where we assume strong longitudinal magnetic field, low beta and high aspect ratio, which allows us to use the set of reduced MHD equations (RMHD). The model is based on a shell technique in the wave vector space orthogonal to the strong magnetic field, while the dependence on the longitudinal coordinate is preserved. Numerical simulations show that injected energy is efficiently stored in the loop where a significant level of magnetic and velocity fluctuations is obtained. Nonlinear interactions give rise to an energy cascade towards smaller scales where energy is dissipated in an intermittent fashion. Due to the strong longitudinal magnetic field, dissipative structures propagate along the loop, with the typical speed of the Alfvén waves. The statistical analysis on the intermittent dissipative events compares well with all observed properties of nanoflare emission statistics. Moreover the recent observations of non thermal velocity measurements during flare occurrence are well described by the numerical results of the simulation model. All these results naturally emerge from the model dynamical evolution without any need of an ad-hoc hypothesis.

3

Sharma, A. Y., M. D. J. Cole, T. Görler, Y. Chen, D. R. Hatch, W. Guttenfelder, R. Hager, et al. "Global gyrokinetic study of shaping effects on electromagnetic modes at NSTX aspect ratio with ad hoc parallel magnetic perturbation effects." Physics of Plasmas 29, no. 11 (November 2022): 112503. http://dx.doi.org/10.1063/5.0106925.

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Plasma shaping may have a stronger effect on global turbulence in tight-aspect-ratio tokamaks than in conventional-aspect-ratio tokamaks due to the higher toroidicity and more acute poloidal asymmetry in the magnetic field. In addition, previous local gyrokinetic studies have shown that it is necessary to include parallel magnetic field perturbations in order to accurately compute growth rates of electromagnetic modes in tight-aspect-ratio tokamaks. In this work, the effects of elongation and triangularity on global, ion-scale, linear electromagnetic modes are studied at National Spherical Torus Experiment (NSTX) aspect ratio and high plasma β using the global gyrokinetic particle-in-cell code XGC. The effects of compressional magnetic perturbations are approximated via a well-known modification to the particle drifts that was developed for flux-tube simulations [Joiner et al., Phys. Plasmas 17, 072104 (2010)], without proof of its validity in a global simulation, with the gyrokinetic codes GENE and GEM being used for local verification and global cross-verification. Magnetic equilibria are re-constructed for each distinct plasma profile that is used. Coulomb collision effects are not considered. Within the limitations imposed by the present study, it is found that linear growth rates of electromagnetic modes (collisionless microtearing modes and kinetic ballooning modes) are significantly reduced in a high-elongation and high-triangularity NSTX-like geometry compared to a circular NSTX-like geometry. For example, growth rates of kinetic ballooning modes at high- β are reduced to the level of that of collisionless trapped electron modes.

4

Wang, Bei, Stephane Ethier, William Tang, Khaled Z. Ibrahim, Kamesh Madduri, Samuel Williams, and Leonid Oliker. "Modern gyrokinetic particle-in-cell simulation of fusion plasmas on top supercomputers." International Journal of High Performance Computing Applications 33, no. 1 (June 29, 2017): 169–88. http://dx.doi.org/10.1177/1094342017712059.

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The gyrokinetic toroidal code at Princeton (GTC-P) is a highly scalable and portable particle-in-cell (PIC) code. It solves the 5-D Vlasov–Poisson equation featuring efficient utilization of modern parallel computer architectures at the petascale and beyond. Motivated by the goal of developing a modern code capable of dealing with the physics challenge of increasing problem size with sufficient resolution, new thread-level optimizations have been introduced as well as a key additional domain decomposition. GTC-P’s multiple levels of parallelism, including internode 2-D domain decomposition and particle decomposition, as well as intranode shared memory partition and vectorization, have enabled pushing the scalability of the PIC method to extreme computational scales. In this article, we describe the methods developed to build a highly parallelized PIC code across a broad range of supercomputer designs. This particularly includes implementations on heterogeneous systems using NVIDIA GPU accelerators and Intel Xeon Phi (MIC) coprocessors and performance comparisons with state-of-the-art homogeneous HPC systems such as Blue Gene/Q. New discovery science capabilities in the magnetic fusion energy application domain are enabled, including investigations of ion–temperature–gradient driven turbulence simulations with unprecedented spatial resolution and long temporal duration. Performance studies with realistic fusion experimental parameters are carried out on multiple supercomputing systems spanning a wide range of cache capacities, cache-sharing configurations, memory bandwidth, interconnects, and network topologies. These performance comparisons using a realistic discovery-science-capable domain application code provide valuable insights on optimization techniques across one of the broadest sets of current high-end computing platforms worldwide.

5

Cranmer, Steven R., and Momchil E. Molnar. "Magnetohydrodynamic Mode Conversion in the Solar Corona: Insights from Fresnel-like Models of Waves at Sharp Interfaces." Astrophysical Journal 955, no. 1 (September 1, 2023): 68. http://dx.doi.org/10.3847/1538-4357/acee6c.

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Abstract The solar atmosphere is known to contain many different types of wave-like oscillation. Waves and other fluctuations (e.g., turbulent eddies) are believed to be responsible for at least some of the energy transport and dissipation that heats the corona and accelerates the solar wind. Thus, it is important to understand the behavior of magnetohydrodynamic (MHD) waves as they propagate and evolve in different regions of the Sun’s atmosphere. In this paper, we investigate how MHD waves can affect the overall plasma state when they reflect and refract at sharp, planar interfaces in density. First, we correct an error in a foundational paper (Stein) that affects the calculation of wave energy-flux conservation. Second, we apply this model to reflection-driven MHD turbulence in the solar wind, where the presence of density fluctuations can enhance the generation of inward-propagating Alfvén waves. This model reproduces the time-averaged Elsässer imbalance fraction (i.e., the ratio of inward to outward Alfvénic power) from several published numerical simulations. Lastly, we model how the complex magnetic field threading the transition region (TR) between the chromosphere and corona helps convert a fraction of upward-propagating Alfvén waves into fast-mode and slow-mode MHD waves. These magnetosonic waves dissipate in a narrow region around the TR and produce a sharp peak in the heating rate. This newly found source of heating sometimes exceeds the expected heating rate from Alfvénic turbulence by an order of magnitude. It may explain why some earlier models seemed to require an additional ad hoc heat source at this location.

6

Dudson, B. D., and J. Leddy. "Hermes: global plasma edge fluid turbulence simulations." Plasma Physics and Controlled Fusion 59, no. 5 (April 4, 2017): 054010. http://dx.doi.org/10.1088/1361-6587/aa63d2.

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7

Grandgirard, V., Y. Sarazin, P. Angelino, A. Bottino, N. Crouseilles, G. Darmet, G. Dif-Pradalier, et al. "Global full-fgyrokinetic simulations of plasma turbulence." Plasma Physics and Controlled Fusion 49, no. 12B (November 15, 2007): B173—B182. http://dx.doi.org/10.1088/0741-3335/49/12b/s16.

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8

Pueschel, M. J., M. Kammerer, and F. Jenko. "Gyrokinetic turbulence simulations at high plasma beta." Physics of Plasmas 15, no. 10 (October 2008): 102310. http://dx.doi.org/10.1063/1.3005380.

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9

Thyagaraja, A. "Direct Numerical Simulations of Two-Fluid Plasma Turbulence." Le Journal de Physique IV 05, no. C6 (October 1995): C6–105—C6–108. http://dx.doi.org/10.1051/jp4:1995621.

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10

Xu, X. Q., W. M. Nevins, R. H. Cohen, J. R. Myra, and P. B. Snyder. "Dynamical simulations of boundary plasma turbulence in divertor geometry." New Journal of Physics 4 (July 24, 2002): 53. http://dx.doi.org/10.1088/1367-2630/4/1/353.

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11

Henriksson, S. V., S. J. Janhunen, T. P. Kiviniemi, and J. A. Heikkinen. "Global spectral investigation of plasma turbulence in gyrokinetic simulations." Physics of Plasmas 13, no. 7 (July 2006): 072303. http://dx.doi.org/10.1063/1.2218330.

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12

Friedman, B., T. A. Carter, M. V. Umansky, D. Schaffner, and I. Joseph. "Nonlinear instability in simulations of Large Plasma Device turbulence." Physics of Plasmas 20, no. 5 (May 2013): 055704. http://dx.doi.org/10.1063/1.4805084.

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13

TenBarge, J. M., G. G. Howes, W. Dorland, and G. W. Hammett. "An oscillating Langevin antenna for driving plasma turbulence simulations." Computer Physics Communications 185, no. 2 (February 2014): 578–89. http://dx.doi.org/10.1016/j.cpc.2013.10.022.

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14

Galassi, Davide, Guido Ciraolo, Patrick Tamain, Hugo Bufferand, Philippe Ghendrih, Nicolas Nace, and Eric Serre. "Tokamak Edge Plasma Turbulence Interaction with Magnetic X-Point in 3D Global Simulations." Fluids 4, no. 1 (March 15, 2019): 50. http://dx.doi.org/10.3390/fluids4010050.

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Turbulence in the edge plasma of a tokamak is a key actor in the determination of the confinement properties. The divertor configuration seems to be beneficial for confinement, suggesting an effect on turbulence of the particular magnetic geometry introduced by the X-point. Simulations with the 3D fluid turbulence code TOKAM3X are performed here to evaluate the impact of a diverted configuration on turbulence in the edge plasma, in an isothermal framework. The presence of the X-point is found, locally, to affect both the shape of turbulent structures and the amplitude of fluctuations, in qualitative agreement with recent experimental observations. In particular, a quiescent region is found in the divertor scrape-off layer (SOL), close to the separatrix. Globally, a mild transport barrier spontaneously forms in the closed flux surfaces region near the separatrix, differently from simulations in limiter configuration. The effect of turbulence-driven Reynolds stress on the formation of the barrier is found to be weak by dedicated simulations, while turbulence damping around the X-point seems to globally reduce turbulent transport on the whole flux surface. The magnetic shear is thus pointed out as a possible element that contributes to the formation of edge transport barriers.

15

Saini, Nadish, and Igor A. Bolotnov. "Two-Phase Turbulence Statistics from High Fidelity Dispersed Droplet Flow Simulations in a Pressurized Water Reactor (PWR) Sub-Channel with Mixing Vanes." Fluids 6, no. 2 (February 6, 2021): 72. http://dx.doi.org/10.3390/fluids6020072.

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In the dispersed flow film boiling regime (DFFB), which exists under post-LOCA (loss-of-coolant accident) conditions in pressurized water reactors (PWRs), there is a complex interplay between droplet dynamics and turbulence in the surrounding steam. Experiments have accredited particular significance to droplet collision with the spacer-grids and mixing vane structures and their consequent positive feedback to the heat transfer recorded in the immediate downstream vicinity. Enabled by high-performance computing (HPC) systems and a massively parallel finite element-based flow solver—PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis)—this work presents high fidelity interface capturing, two-phase, adiabatic simulations in a PWR sub-channel with spacer grids and mixing vanes. Selected flow conditions for the simulations are informed by the experimental data found in the literature, including the steam Reynolds number and collision Weber number (Wec={40,80}), and are characteristic of the DFFB regime. Data were collected from the simulations at an unprecedented resolution, which provides detailed insights into the continuous phase turbulence statistics, highlighting the effects of the presence of droplets and the comparative effect of different Weber numbers on turbulence in the surrounding steam. Further, axial evolution of droplet dynamics was analyzed through cross-sectionally averaged quantities, including droplet volume, surface area and Sauter mean diameter (SMD). The downstream SMD values agree well with the existing empirical correlations for the selected range of Wec. The high-resolution data repository from the simulations herein is expected to be of significance to guide model development for system-level thermal hydraulic codes.

16

Meringolo, Claudio, Alejandro Cruz-Osorio, Luciano Rezzolla, and Sergio Servidio. "Microphysical Plasma Relations from Special-relativistic Turbulence." Astrophysical Journal 944, no. 2 (February 1, 2023): 122. http://dx.doi.org/10.3847/1538-4357/acaefe.

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Abstract The microphysical, kinetic properties of astrophysical plasmas near accreting compact objects are still poorly understood. For instance, in modern general-relativistic magnetohydrodynamic simulations, the relation between the temperature of electrons T e and protons T p is prescribed in terms of simplified phenomenological models where the electron temperature is related to the proton temperature in terms of the ratio between the gas and magnetic pressures, or the β parameter. We here present a very comprehensive campaign of two-dimensional kinetic particle-in-cell simulations of special-relativistic turbulence to investigate systematically the microphysical properties of the plasma in the transrelativistic regime. Using a realistic mass ratio between electrons and protons, we analyze how the index of the electron energy distributions κ, the efficiency of nonthermal particle production  , and the temperature ratio  := T e / T p vary over a wide range of values of β and σ. For each of these quantities, we provide two-dimensional fitting functions that describe their behavior in the relevant space of parameters, thus connecting the microphysical properties of the plasma, κ,  , and  , with the macrophysical ones β and σ. In this way, our results can find application in a wide range of astrophysical scenarios, including the accretion and the jet emission onto supermassive black holes, such as M87* and Sgr A*.

17

Perrone, D., T. Passot, D. Laveder, F. Valentini, P. L. Sulem, I. Zouganelis, P. Veltri, and S. Servidio. "Fluid simulations of plasma turbulence at ion scales: Comparison with Vlasov-Maxwell simulations." Physics of Plasmas 25, no. 5 (May 2018): 052302. http://dx.doi.org/10.1063/1.5026656.

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18

Meyrand, Romain, Anjor Kanekar, William Dorland, and Alexander A. Schekochihin. "Fluidization of collisionless plasma turbulence." Proceedings of the National Academy of Sciences 116, no. 4 (January 4, 2019): 1185–94. http://dx.doi.org/10.1073/pnas.1813913116.

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In a collisionless, magnetized plasma, particles may stream freely along magnetic field lines, leading to “phase mixing” of their distribution function and consequently, to smoothing out of any “compressive” fluctuations (of density, pressure, etc.). This rapid mixing underlies Landau damping of these fluctuations in a quiescent plasma—one of the most fundamental physical phenomena that makes plasma different from a conventional fluid. Nevertheless, broad power law spectra of compressive fluctuations are observed in turbulent astrophysical plasmas (most vividly, in the solar wind) under conditions conducive to strong Landau damping. Elsewhere in nature, such spectra are normally associated with fluid turbulence, where energy cannot be dissipated in the inertial-scale range and is, therefore, cascaded from large scales to small. By direct numerical simulations and theoretical arguments, it is shown here that turbulence of compressive fluctuations in collisionless plasmas strongly resembles one in a collisional fluid and does have broad power law spectra. This “fluidization” of collisionless plasmas occurs, because phase mixing is strongly suppressed on average by “stochastic echoes,” arising due to nonlinear advection of the particle distribution by turbulent motions. Other than resolving the long-standing puzzle of observed compressive fluctuations in the solar wind, our results suggest a conceptual shift for understanding kinetic plasma turbulence generally: rather than being a system where Landau damping plays the role of dissipation, a collisionless plasma is effectively dissipationless, except at very small scales. The universality of “fluid” turbulence physics is thus reaffirmed even for a kinetic, collisionless system.

19

Janhunen, Salomon, Gabriele Merlo, Alexey Gurchenko, Evgeniy Gusakov, Frank Jenko, and Timo Kiviniemi. "Simulation of transport in the FT-2 tokamak up to the electron scale with GENE." Plasma Physics and Controlled Fusion 64, no. 1 (November 26, 2021): 015005. http://dx.doi.org/10.1088/1361-6587/ac318c.

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Abstract Prior experimental work on the FT-2 tokamak has observed electron density fluctuations at electron Larmor radius scales using the enhanced scattering (ES) diagnostic (Gusakov et al 2006 Plasma Phys. Control. Fusion 48 A371–6, Gurchenko and Gusakov 2010 Plasma Phys. Control. Fusion 52 124035). Gyrokinetic GENE simulations of conditions at the upper hybrid resonance layer probed by the ES diagnostic show the presence of the anticipated turbulence from the electron temperature gradient (ETG) driven instability in linear and nonlinear simulations. Ion-scale turbulence is responsible for majority of the transport via trapped electron modes, while impurities act to merge the spectrum of the ion and the electron scale instabilities into a continuum. The linear spectrum at electron scales is characterized by maximal growth rate at a significant ballooning angle θ 0, and at ion scales the turbulence is broad in the ballooning angle distribution. The neoclassical shearing rate obtained from GENE breaks symmetry in nonlinear simulations of ETG turbulence, which manifests itself as an asymmetric turbulence spectrum. The electron density fluctuation spectrum obtained with GENE corresponds well to the ES measurement at electron scales, as do the fluxes obtained from the ion-scale simulations.

20

Oughton, S., W. H. Matthaeus, M. Wan, and K. T. Osman. "Anisotropy in solar wind plasma turbulence." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, no. 2041 (May 13, 2015): 20140152. http://dx.doi.org/10.1098/rsta.2014.0152.

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A review of spectral anisotropy and variance anisotropy for solar wind fluctuations is given, with the discussion covering inertial range and dissipation range scales. For the inertial range, theory, simulations and observations are more or less in accord, in that fluctuation energy is found to be primarily in modes with quasi-perpendicular wavevectors (relative to a suitably defined mean magnetic field), and also that most of the fluctuation energy is in the vector components transverse to the mean field. Energy transfer in the parallel direction and the energy levels in the parallel components are both relatively weak. In the dissipation range, observations indicate that variance anisotropy tends to decrease towards isotropic levels as the electron gyroradius is approached; spectral anisotropy results are mixed. Evidence for and against wave interpretations and turbulence interpretations of these features will be discussed. We also present new simulation results concerning evolution of variance anisotropy for different classes of initial conditions, each with typical background solar wind parameters.

21

Zhdankin, Vladimir. "Particle Energization in Relativistic Plasma Turbulence: Solenoidal versus Compressive Driving." Astrophysical Journal 922, no. 2 (November 29, 2021): 172. http://dx.doi.org/10.3847/1538-4357/ac222e.

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Abstract Many high-energy astrophysical systems contain magnetized collisionless plasmas with relativistic particles, in which turbulence can be driven by an arbitrary mixture of solenoidal and compressive motions. For example, turbulence in hot accretion flows may be driven solenoidally by the magnetorotational instability or compressively by spiral shock waves. It is important to understand the role of the driving mechanism on kinetic turbulence and the associated particle energization. In this work, we compare particle-in-cell simulations of solenoidally driven turbulence with similar simulations of compressively driven turbulence. We focus on plasma that has an initial beta of unity, relativistically hot electrons, and varying ion temperature. Apart from strong large-scale density fluctuations in the compressive case, the turbulence statistics are similar for both drives, and the bulk plasma is described reasonably well by an isothermal equation of state. We find that nonthermal particle acceleration is more efficient when turbulence is driven compressively. In the case of relativistically hot ions, both driving mechanisms ultimately lead to similar power-law particle energy distributions, but over a different duration. In the case of nonrelativistic ions, there is significant nonthermal particle acceleration only for compressive driving. Additionally, we find that the electron-to-ion heating ratio is less than unity for both drives, but takes a smaller value for compressive driving. We demonstrate that this additional ion energization is associated with the collisionless damping of large-scale compressive modes via perpendicular electric fields.

22

Hellinger, Petr, Victor Montagud-Camps, Luca Franci, Lorenzo Matteini, Emanuele Papini, Andrea Verdini, and Simone Landi. "Ion-scale Transition of Plasma Turbulence: Pressure–Strain Effect." Astrophysical Journal 930, no. 1 (May 1, 2022): 48. http://dx.doi.org/10.3847/1538-4357/ac5fad.

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Abstract We investigate properties of solar-wind-like plasma turbulence using direct numerical simulations. We analyze the transition from large, magnetohydrodynamic (MHD) scales to the ion characteristic ones using two-dimensional hybrid (fluid electrons and kinetic ions) simulations. To capture and quantify turbulence properties, we apply the Karman–Howarth–Monin (KHM) equation for compressible Hall–MHD (extended by considering the plasma pressure as a tensor quantity) to the numerical results. The KHM analysis indicates that the transition from MHD to ion scales (the so-called ion break in the power spectrum) results from a combination of an onset of Hall physics and an effective dissipation owing to the pressure–strain energy-exchange channel and resistivity. We discuss the simulation results in the context of the solar wind.

23

Lee, Sang-Yun, L. F. Ziebell, P. H. Yoon, R. Gaelzer, and E. S. Lee. "Particle-in-cell and Weak Turbulence Simulations of Plasma Emission." Astrophysical Journal 871, no. 1 (January 23, 2019): 74. http://dx.doi.org/10.3847/1538-4357/aaf476.

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24

Bernard, T. N., E. L. Shi, K. W. Gentle, A. Hakim, G. W. Hammett, T. Stoltzfus-Dueck, and E. I. Taylor. "Gyrokinetic continuum simulations of plasma turbulence in the Texas Helimak." Physics of Plasmas 26, no. 4 (April 2019): 042301. http://dx.doi.org/10.1063/1.5085457.

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25

Fogaccia, G., R. Benzi, and F. Romanelli. "Lattice Boltzmann algorithm for three-dimensional simulations of plasma turbulence." Physical Review E 54, no. 4 (October 1, 1996): 4384–93. http://dx.doi.org/10.1103/physreve.54.4384.

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Tang, William, Bei Wang, and Stephane Ethier. "Scientific Discovery in Fusion Plasma Turbulence Simulations at Extreme Scale." Computing in Science & Engineering 16, no. 5 (September 2014): 44–52. http://dx.doi.org/10.1109/mcse.2014.54.

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Thyagaraja, A. "Numerical simulations of tokamak plasma turbulence and internal transport barriers." Plasma Physics and Controlled Fusion 42, no. 12B (December 1, 2000): B255—B269. http://dx.doi.org/10.1088/0741-3335/42/12b/320.

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28

Waltz, R. E., and R. L. Miller. "Ion temperature gradient turbulence simulations and plasma flux surface shape." Physics of Plasmas 6, no. 11 (November 1999): 4265–71. http://dx.doi.org/10.1063/1.873694.

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29

Ross, David W., and William Dorland. "Comparing simulation of plasma turbulence with experiment. II. Gyrokinetic simulations." Physics of Plasmas 9, no. 12 (December 2002): 5031–35. http://dx.doi.org/10.1063/1.1518997.

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30

Oppenheim, Meers M., and Yakov S. Dimant. "First 3-D simulations of meteor plasma dynamics and turbulence." Geophysical Research Letters 42, no. 3 (February 9, 2015): 681–87. http://dx.doi.org/10.1002/2014gl062411.

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31

Vega, Cristian, Stanislav Boldyrev, and Vadim Roytershteyn. "Spectra of Magnetic Turbulence in a Relativistic Plasma." Astrophysical Journal Letters 931, no. 1 (May 1, 2022): L10. http://dx.doi.org/10.3847/2041-8213/ac6cde.

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Abstract We present a phenomenological and numerical study of strong Alfvénic turbulence in a magnetically dominated collisionless relativistic plasma with a strong background magnetic field. In contrast with the nonrelativistic case, the energy in such turbulence is contained in magnetic and electric fluctuations. We argue that such turbulence is analogous to turbulence in a strongly magnetized nonrelativistic plasma in the regime of broken quasi-neutrality. Our 2D particle-in-cell numerical simulations of turbulence in a relativistic pair plasma find that the spectrum of the total energy has the scaling k −3/2, while the difference between the magnetic and electric energies, the so-called residual energy, has the scaling k −2.4. The electric and magnetic fluctuations at scale ℓ exhibit dynamic alignment with the alignment angle scaling close to cos ϕ ℓ ∝ ℓ 1 / 4 . At scales smaller than the (relativistic) plasma inertial scale, the energy spectrum of relativistic inertial Alfvén turbulence steepens to k −3.5.

32

Papadopoulos, Aristeides D., Johan Anderson, Eun-jin Kim, Michail Mavridis, and Heinz Isliker. "Statistical Analysis of Plasma Dynamics in Gyrokinetic Simulations of Stellarator Turbulence." Entropy 25, no. 6 (June 15, 2023): 942. http://dx.doi.org/10.3390/e25060942.

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A geometrical method for assessing stochastic processes in plasma turbulence is investigated in this study. The thermodynamic length methodology allows using a Riemannian metric on the phase space; thus, distances between thermodynamic states can be computed. It constitutes a geometric methodology to understand stochastic processes involved in, e.g., order–disorder transitions, where a sudden increase in distance is expected. We consider gyrokinetic simulations of ion-temperature-gradient (ITG)-mode-driven turbulence in the core region of the stellarator W7-X with realistic quasi-isodynamic topologies. In gyrokinetic plasma turbulence simulations, avalanches, e.g., of heat and particles, are often found, and in this work, a novel method for detection is investigated. This new method combines the singular spectrum analysis algorithm with a hierarchical clustering method such that the time series is decomposed into two parts: useful physical information and noise. The informative component of the time series is used for the calculation of the Hurst exponent, the information length, and the dynamic time. Based on these measures, the physical properties of the time series are revealed.

33

Vega, Cristian, Stanislav Boldyrev, and Vadim Roytershteyn. "Spatial Intermittency of Particle Distribution in Relativistic Plasma Turbulence." Astrophysical Journal 949, no. 2 (June 1, 2023): 98. http://dx.doi.org/10.3847/1538-4357/accd73.

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Abstract Relativistic magnetically dominated turbulence is an efficient engine for particle acceleration in a collisionless plasma. Ultrarelativistic particles accelerated by interactions with turbulent fluctuations form nonthermal power-law distribution functions in the momentum (or energy) space, f(γ)d γ ∝ γ −α d γ, where γ is the Lorenz factor. We argue that in addition to exhibiting non-Gaussian distributions over energies, particles energized by relativistic turbulence also become highly intermittent in space. Based on particle-in-cell numerical simulations and phenomenological modeling, we propose that the bulk plasma density has lognormal statistics, while the density of the accelerated particles, n, has a power-law distribution function, P ( n ) dn ∝ n − β dn . We argue that the scaling exponents are related as β ≈ α + 1, which is broadly consistent with numerical simulations. Non-space-filling, intermittent distributions of plasma density and energy fluctuations may have implications for plasma heating and for radiation produced by relativistic turbulence.

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Hankla, Amelia M., Vladimir Zhdankin, Gregory R. Werner, Dmitri A. Uzdensky, and Mitchell C. Begelman. "Kinetic simulations of imbalanced turbulence in a relativistic plasma: Net flow and particle acceleration." Monthly Notices of the Royal Astronomical Society 509, no. 3 (November 10, 2021): 3826–41. http://dx.doi.org/10.1093/mnras/stab3209.

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ABSTRACT Turbulent high-energy astrophysical systems often feature asymmetric energy injection: for instance, Alfvén waves propagating from an accretion disc into its corona. Such systems are ‘imbalanced’: the energy fluxes parallel and antiparallel to the large-scale magnetic field are unequal. In the past, numerical studies of imbalanced turbulence have focused on the magnetohydrodynamic regime. In this study, we investigate externally driven imbalanced turbulence in a collision-less, ultrarelativistically hot, magnetized pair plasma using 3D particle-in-cell (PIC) simulations. We find that the injected electromagnetic momentum efficiently converts into plasma momentum, resulting in net motion along the background magnetic field with speeds up to a significant fraction of lightspeed. This discovery has important implications for the launching of accretion disc winds. We also find that although particle acceleration in imbalanced turbulence operates on a slower time-scale than in balanced turbulence, it ultimately produces a power-law energy distribution similar to balanced turbulence. Our results have ramifications for black hole accretion disc coronae, winds, and jets.

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Trotta, Domenico, Francesco Valentini, David Burgess, and Sergio Servidio. "Phase space transport in the interaction between shocks and plasma turbulence." Proceedings of the National Academy of Sciences 118, no. 21 (May 18, 2021): e2026764118. http://dx.doi.org/10.1073/pnas.2026764118.

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The interaction of collisionless shocks with fully developed plasma turbulence is numerically investigated. Hybrid kinetic simulations, where a turbulent jet is slammed against an oblique shock, are employed to address the role of upstream turbulence on plasma transport. A technique, using coarse graining of the Vlasov equation, is proposed, showing that the particle transport strongly depends on upstream turbulence properties, such as strength and coherency. These results might be relevant for the understanding of acceleration and heating processes in space plasmas.

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Zheng, S. Y., D. B. Zhang, E. B. Xue, L. M. Yu, X. M. Zhang, J. Huang, Y. Xiao, M. Q. Wu, and X. Z. Gong. "Study of turbulence in the high β _P discharge using only RF heating on EAST." Plasma Physics and Controlled Fusion 64, no. 4 (February 28, 2022): 045017. http://dx.doi.org/10.1088/1361-6587/ac4b07.

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Abstract High poloidal beta scenarios with a favorable energy confinement ( β p ∼ 1.9 , H 98 y 2 ∼ 1.4 ) have been achieved on the Experimental Advanced Superconducting Tokamak using only radio frequency wave heating. Gyrokinetic simulations are carried out with experimental plasma parameters and tokamak equilibrium data of a typical high β p discharge using the gyrokinetic toroidal code. Linear simulations show that electron-temperature scale length and electron-density scale length destabilize the turbulence, collision effects stabilize the turbulence, and the instability propagates in the electron diamagnetic direction. These properties indicate that the dominant instability in the core of high β p plasma is a collisionless trapped electron mode. Ion thermal diffusivity, calculated by nonlinear gyrokinetic simulations, is consistent with the experimental value, in which the electron collision effects play an important role. Further analyses show that instabilities with 0.38$?> k θ ρ s > 0.38 are suppressed by collision effects and collision effects reduce the radial correlation length of turbulence, resulting in the suppression of the turbulence.

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Dyrud, L. P., J. Urbina, J. T. Fentzke, E. Hibbit, and J. Hinrichs. "Global variation of meteor trail plasma turbulence." Annales Geophysicae 29, no. 12 (December 16, 2011): 2277–86. http://dx.doi.org/10.5194/angeo-29-2277-2011.

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Abstract. We present the first global simulations on the occurrence of meteor trail plasma irregularities. These results seek to answer the following questions: when a meteoroid disintegrates in the atmosphere, will the resulting trail become plasma turbulent? What are the factors influencing the development of turbulence? and how do these trails vary on a global scale? Understanding meteor trail plasma turbulence is important because turbulent meteor trails are visible as non-specular trails to coherent radars. Turbulence also influences the evolution of specular radar meteor trails; this fact is important for the inference of mesospheric temperatures from the trail diffusion rates, and their usage for meteor burst communication. We provide evidence of the significant effect that neutral atmospheric winds and ionospheric plasma density have on the variability of meteor trail evolution and on the observation of non-specular meteor trails. We demonstrate that trails are far less likely to become and remain turbulent in daylight, explaining several observational trends for non-specular and specular meteor trails.

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ELIASSON, BENGT. "FULL-SCALE SIMULATIONS OF IONOSPHERIC LANGMUIR TURBULENCE." Modern Physics Letters B 27, no. 08 (March 13, 2013): 1330005. http://dx.doi.org/10.1142/s0217984913300056.

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This brief review is devoted to full-scale numerical modeling of the nonlinear interactions between electromagnetic (EM) waves and the ionosphere, giving rise to ionospheric Langmuir turbulence. A numerical challenge in the full-scale modeling is that it involves very different length- and time-scales. While the EM waves have wavelengths of the order 100 meters, the ionospheric Langmuir turbulence involving electrostatic waves and nonlinear structures can have wavelengths below one meter. A full-scale numerical scheme must resolve these different length- and time-scales, as well as the ionospheric profile extending vertically hundreds of kilometers. To overcome severe limitations on the timestep and computational load, a non-uniform nested grid method has been devised, in which the EM wave is represented in space on a relatively coarse grid with a spacing of a few meters, while the electrostatic wave turbulence is locally resolved on a much denser grid in space at the critical layer where the turbulence occurs. Interpolation and averaging schemes are used to communicate values of the EM fields and current sources between the coarse and dense grids. In this manner, the computational load can be drastically decreased, making it possible to perform full-scale simulations that cover the different time- and space-scales. We discuss the simulation methods and how they are used to study turbulence, stimulated EM emissions, particle acceleration and heating, and the formation of artificial ionospheric plasma layers by ionospheric Langmuir turbulence.

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Sisti, M., S. Fadanelli, S. S. Cerri, M. Faganello, F. Califano, and O. Agullo. "Characterizing current structures in 3D hybrid-kinetic simulations of plasma turbulence." Astronomy & Astrophysics 655 (November 2021): A107. http://dx.doi.org/10.1051/0004-6361/202141902.

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Context. In space and astrophysical plasmas, turbulence leads to the development of coherent structures characterized by a strong current density and important magnetic shears. Aims. Using hybrid-kinetic simulations of turbulence (3D with different energy injection scales), we investigate the development of these coherent structures and characterize their shape. Methods. First, we present different methods to estimate the overall shape of the 3D structure using local measurements, foreseeing an application on satellite data. Then we study the local magnetic configuration inside and outside current peak regions, comparing the statistics in the two cases. Last, we compare the statistical properties of the local configuration obtained in simulations with the ones obtained analyzing an MMS (Magnetospheric MultiScale mission) dataset having similar plasma parameters. Results. Thanks to our analysis, (1) we validate the possibility of studying the overall shape of 3D structures using local methods, (2) we provide an overview of a local magnetic configuration emerging in different turbulent regimes, (3) we show that our 3D-3V simulations can reproduce the structures that emerge in MMS data for the periods considered.

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Ricketson, L., A. Hakim, and J. Hittinger. "Consistent coupling algorithms for coupled core-edge simulations of plasma turbulence." Physics of Plasmas 28, no. 1 (January 2021): 012301. http://dx.doi.org/10.1063/5.0027670.

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Franci, Luca, Simone Landi, Lorenzo Matteini, Andrea Verdini, and Petr Hellinger. "HIGH-RESOLUTION HYBRID SIMULATIONS OF KINETIC PLASMA TURBULENCE AT PROTON SCALES." Astrophysical Journal 812, no. 1 (October 5, 2015): 21. http://dx.doi.org/10.1088/0004-637x/812/1/21.

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Perrone, D., F. Valentini, S. Servidio, S. Dalena, and P. Veltri. "VLASOV SIMULATIONS OF MULTI-ION PLASMA TURBULENCE IN THE SOLAR WIND." Astrophysical Journal 762, no. 2 (December 19, 2012): 99. http://dx.doi.org/10.1088/0004-637x/762/2/99.

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Goodman, Simon, Hideyuki Usui, and Hiroshi Matsumoto. "Particle‐in‐cell (PIC) simulations of electromagnetic emissions from plasma turbulence." Physics of Plasmas 1, no. 6 (June 1994): 1765–67. http://dx.doi.org/10.1063/1.870680.

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Ottaviani, M. "An alternative approach to field-aligned coordinates for plasma turbulence simulations." Physics Letters A 375, no. 15 (April 2011): 1677–85. http://dx.doi.org/10.1016/j.physleta.2011.02.069.

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Angioni, C., J. Candy, E. Fable, M. Maslov, A. G. Peeters, R. E. Waltz, and H. Weisen. "Particle pinch and collisionality in gyrokinetic simulations of tokamak plasma turbulence." Physics of Plasmas 16, no. 6 (June 2009): 060702. http://dx.doi.org/10.1063/1.3155498.

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Hariri, F., and M. Ottaviani. "A flux-coordinate independent field-aligned approach to plasma turbulence simulations." Computer Physics Communications 184, no. 11 (November 2013): 2419–29. http://dx.doi.org/10.1016/j.cpc.2013.06.005.

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Tamain, P., H. Bufferand, L. Carbajal, Y. Marandet, C. Baudoin, G. Ciraolo, C. Colin, et al. "Interplay between Plasma Turbulence and Particle Injection in 3D Global Simulations." Contributions to Plasma Physics 56, no. 6-8 (July 4, 2016): 569–74. http://dx.doi.org/10.1002/ctpp.201610063.

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Bañón Navarro, A., A. Di Siena, J. L. Velasco, F. Wilms, G. Merlo, T. Windisch, L. L. LoDestro, J. B. Parker, and F. Jenko. "First-principles based plasma profile predictions for optimized stellarators." Nuclear Fusion 63, no. 5 (March 22, 2023): 054003. http://dx.doi.org/10.1088/1741-4326/acc3af.

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Abstract In the present Letter, first-of-its-kind computer simulations predicting plasma profiles for modern optimized stellarators—while self-consistently retaining neoclassical transport, turbulent transport with 3D effects, and external physical sources—are presented. These simulations exploit a newly developed coupling framework involving the global gyrokinetic turbulence code GENE-3D, the neoclassical transport code KNOSOS, and the 1D transport solver TANGO. This framework is used to analyze the recently observed degradation of energy confinement in electron-heated plasmas in the Wendelstein 7-X stellarator, where the central ion temperature was ‘clamped’ to T i ≈ 1.5 keV regardless of the external heating power. By performing first-principles based simulations, we provide key evidence to understand this effect, namely the inefficient thermal coupling between electrons and ions in a turbulence-dominated regime, which is exacerbated by the large T e / T i ratios, and show that a more efficient ion heat source, such as direct ion heating, will increase the on-axis ion temperature. This work paves the way towards the use of high-fidelity models for the development of the next generation of stellarators, in which neoclassical and turbulent transport are optimized simultaneously.

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Santos-Lima, R., G. Guerrero, E. M. de Gouveia Dal Pino, and A. Lazarian. "Diffusion of large-scale magnetic fields by reconnection in MHD turbulence." Monthly Notices of the Royal Astronomical Society 503, no. 1 (February 18, 2021): 1290–309. http://dx.doi.org/10.1093/mnras/stab470.

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ABSTRACT The rate of magnetic field diffusion plays an essential role in several astrophysical plasma processes. It has been demonstrated that the omnipresent turbulence in astrophysical media induces fast magnetic reconnection, which consequently leads to large-scale magnetic flux diffusion at a rate independent of the plasma microphysics. This process is called 'reconnection diffusion' (RD) and allows for the diffusion of fields, which are dynamically important. The current theory describing RD is based on incompressible magnetohydrodynamic (MHD) turbulence. In this work, we have tested quantitatively the predictions of the RD theory when magnetic forces are dominant in the turbulence dynamics (Alfvénic Mach number MA < 1). We employed the Pencil Code to perform numerical simulations of forced MHD turbulence, extracting the values of the diffusion coefficient ηRD using the test-field method. Our results are consistent with the RD theory ($\eta _{\rm RD} \sim M_{\rm A}^{3}$ for MA < 1) when turbulence approaches the incompressible limit (sonic Mach number MS ≲ 0.02), while for larger MS the diffusion is faster ($\eta _{\rm RD} \sim M_{\rm A}^{2}$). This work shows for the first time simulations of compressible MHD turbulence with the suppression of the cascade in the direction parallel to the mean magnetic field, which is consistent with incompressible weak turbulence theory. We also verified that in our simulations the energy cascading time does not follow the scaling with MA predicted for the weak regime, in contradiction with the RD theory assumption. Our results generally support and expand the RD theory predictions.

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Comişel, Horia, Yasuhiro Nariyuki, Yasuhito Narita, and Uwe Motschmann. "On the role of ion-scale whistler waves in space and astrophysical plasma turbulence." Annales Geophysicae 34, no. 11 (November 9, 2016): 975–84. http://dx.doi.org/10.5194/angeo-34-975-2016.

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Abstract. Competition of linear mode waves is studied numerically to understand the energy cascade mechanism in plasma turbulence on ion-kinetic scales. Hybrid plasma simulations are performed in a 3-D simulation box by pumping large-scale Alfvén waves on the fluid scale. The result is compared with that from our earlier 2-D simulations. We find that the whistler mode is persistently present both in the 2-D and 3-D simulations irrespective of the initial setup, e.g., the amplitude of the initial pumping waves, while all the other modes are excited and damped such that the energy is efficiently transported to thermal energy over non-whistler mode. The simulation results suggest that the whistler mode could transfer the fluctuation energy smoothly from the fluid scale down to the electron-kinetic scale, and justifies the notion of whistler turbulence.