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Seminars (GYP)

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Event When Speaker Title Presentation Material
GYPW01 19th July 2010
09:45 to 10:30
S Cowley Multiscale turbulence in Fusion and Gyrokinetics
GYPW01 19th July 2010
11:30 to 12:15
Observational evidence for anisotropic solar wind turbulence on fluid and kinetic scales
The interaction between small scale turbulence (of the order of the ion Larmor radius) and meso scale magnetic islands is investigated within the gyrokinetic framework. Turbulence, driven by background temperature and density gradients, over nonlinear mode coupling, pumps energy into long wave length modes, and can result in an electrostatic vortex mode that coincides with the magnetic island. The strength of the vortex is strongly enhanced by the modified plasma flow response connected with the change in topology, and the transport it generates can compete with the parallel motion along the perturbed magnetic field. Density and temperature gradients inside the island are below the threshold for turbulence generation, and the anomalous transport inside the island is determined by turbulence spreading. A finite radial temperature gradient inside the island is observed to persist despite the fast motion along the field, and is related to the trapped particles which do not move along the field around the island. Consequences for the stability of the neo-classical tearing mode are discussed.
GYPW01 19th July 2010
14:00 to 14:30
Measurements of electron temperature fluctuations on DIII-D
GYPW01 19th July 2010
14:30 to 15:00
Long-wavelength turbulence characteristics, dynamics and flows in tokamak plasmas
Plasma turbulence, driven by temperature and density gradients inherent to magnetically confined plasmas, drives cross-field transport of particles, energy and momentum. The basic characteristics of density turbulence in a tokamak plasma are presented along with their scaling behavior with respect to certain dimensionless variables (e.g., rho_i/a, ion gyroradius normalized to plasma radius). These turbulence features presented are experimentally measured with a spectroscopic diagnostic, Beam Emission Spectroscopy (BES), that measures localized, long-wavelength (k_perp*rho_i
GYPW01 19th July 2010
15:00 to 15:30
Multi-scale turbulence, electron transport, and zonal flows in DIII-D
GYPW01 19th July 2010
15:30 to 16:00
T Rhodes Multi-scale/multi-field turbulence measurements to test gyrokinetic simulation predictions on the DIII-D tokamak
This presentation describes the progress in our ability to rigorously test gyrokinetic turbulence simulations through a series of carefully designed experiments performed within the Transport Mode Validation Task Force (TMV). These experiments take full advantage of the diagnostic, heating, and plasma control capabilities available at DIII-D. In total, these provide significant constraints for testing and validating gyrokinetic simulations. New, multi-field, multi-scale fluctuation measurements, over a range of target plasmas and radii (r/a~0.55-0.85) have been obtained. New measurements include local, wavenumber resolved TEM scale ñ, fluctuating turbulence flows, density-temperature crossphase, as well as previously available ITG and ETG scale n_e and low-k T_e fluctuations. The methodology, issues, and goals of the TMV will be presented and discussed. Example comparisons between measurements and simulation will be presented with a focus on high-k ETG scale density fluctuations. These, and similar validation efforts, are crucial in developing a predictive capability for ITER and an understanding of the actual ITER plasmas when they arrive. This work was supported by the US Department of Energy under DE-FG02-08ER54984, DE-AC05-76OR00033, and DE-FC02-04ER54698. T.L. Rhodes1, C.H. Holland2, J.C. DeBoo3, A.E. White1, K.H. Burrell3, J. Candy3, E.J. Doyle1, J.C. Hillesheim1, G.R. McKee4, D. Mikkelsen5, W.A. Peebles1, C.C. Petty3, R. Prater3, L. Schmitz1, R.E. Waltz3, G. Wang1, Z. Yan4, and L. Zeng1 1University of California-Los Angeles, PO Box 957099, Los Angeles, CA 90095-7099, USA 2University of California-San Diego, 9500 Gilman Dr., La Jolla, California 92093, USA 3General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA 4University of Wisconsin-Madison, 1500 Engineering Dr., Madison, WI 53706, USA 5Princeton Plasma Physics
GYPW01 20th July 2010
09:00 to 09:45
Measurements and gyrokinetic simulations of electron transport in NSTX
GYPW01 20th July 2010
09:45 to 10:30
Measurements and modelling of turbulent transport on Tore Supra
GYPW01 20th July 2010
11:30 to 12:15
M Maksimovic Solar wind electrons: basic properties and physics
GYPW01 20th July 2010
14:00 to 14:45
F Jenko Grasping plasma turbulence fundamentals: Where do we stand?
GYPW01 20th July 2010
15:00 to 16:00
Experimentalists are from Mars, theoreticians are from Venus: what ones want from the others
GYPW01 21st July 2010
09:00 to 09:45
Waves and fluctuations associated with local instabilities in the solar wind
GYPW01 21st July 2010
09:45 to 10:30
Solar wind ion and electron distribution functions and the transition from fluid to kinetic behaviour
GYPW01 21st July 2010
11:30 to 12:15
T Passot Dispersive Alfvén-wave turbulence and the role of self-generated temperature anisotropy
GYPW01 21st July 2010
14:00 to 14:45
W Dorland Gyrokinetics outside of tokamaks
GYPW01 21st July 2010
14:45 to 15:30
F Zonca Alfvénic turbulence in tokamaks: from micro- to meso-scale fluctuations
The challenge of understanding fast particle collective behaviors in burning plasmas of fusion interest, such as charged fusion products and supra-thermal particles produced by additional heating and current-drive methods, is to develop a predictive capability for describing energetic particle confinement and its link to the dynamic evolution of thermal plasma profiles. This work focuses on aspects of fluctuation induced fast particle transport, involving both micro- and meso-scales. While micro-turbulence induced transport of energetic particles tends to be diffusive and reduced by finite orbit averaging, meso-scale fluctuations exhibit both coherent and incoherent non-linear behaviors, reflecting the nature of convective and diffusive transport events respectively connected with them. Meanwhile, cross-scale couplings in (w,k) space will play a crucial role in reactor relevant plasmas, where they can influence long time-scale behaviors, and will be mediated by zonal structures, e.g. zonal flows, geodesic acoustic modes and structure formation in the particle phase-space. Characteristic aspects of Alfvénic fluctuations in the Alfvén-acoustic frequency range are discussed here, with emphasis on excitation mechanisms due to thermal plasma free energy sources at short wavelength and to wave-particle interactions with the supra-thermal component at the longer scales. The dense spectrum of Alfvénic fluctuations, expected to dominate burning plasmas of fusion interest, poses challenging and largely unexplored issues connected with fast particle transports at all scales. The main focus of this presentation is the convective transport associated with coherent nonlinear wave-particle dynamics, where fundamental roles are played by plasma non-uniformities and peculiar features of toroidal geometries.
GYPW01 21st July 2010
16:30 to 16:50
Entropy cascade in 2D-2V Vlasov-hybrid electrostatic model
GYPW01 21st July 2010
17:10 to 17:30
Fluid models of free energy cascade dynamics
GYPW01 22nd July 2010
09:00 to 09:45
Internal transport barriers in JET and the impact of magnetic ripple and plasma rotation
GYPW01 22nd July 2010
09:45 to 10:30
Spontaneous tokamak rotation: observations turbulent momentum transport has to explain
Ideal tokamaks have axisymmetric magnetic fields that, by symmetry, cannot impart toroidal angular momentum. Yet, even without obvious external sources of momentum, such as neutral-beams, they rotate at speeds up to a substantial fraction of the ion thermal speed. This spontaneous rotation is an unequivocal signature of momentum transport (presumably turbulent) *up* the velocity gradient --- that is, in the opposite direction to any supposed shear viscosity. Theoretical suggestions for the mechanisms producing spontaneous rotation exist; but even qualitative confrontation of theory with experiment is at a rudimentary stage. This presentation will summarize some key experimental observations that require explanation. Understanding the spontaneous rotation is vital for future devices like ITER, where beam-driven rotation will be small, and might be relevant also in the space and astrophysical context.
GYPW01 22nd July 2010
11:30 to 12:15
Transport in Disks and Stars
GYPW01 22nd July 2010
14:00 to 14:30
Toroidal momentum transport
GYPW01 22nd July 2010
14:30 to 15:00
Momentum balance in toroidal plasmas
GYPW01 22nd July 2010
15:00 to 15:30
Rotational shear in tokamak plasmas
GYPW01 22nd July 2010
15:30 to 16:00
F I Parra Transport bifurcations in rotating tokamak plasmas
GYPW01 23rd July 2010
09:00 to 09:45
Studies of waves, turbulence, and transport in the Large Plasma Device
GYPW01 23rd July 2010
09:45 to 10:30
Electrostatic instabilities, turbulence and fast ion interactions in simple magnetised plasma
Electrostatic turbulence, related structures and their effect on particle, heat and momentum transport are investigated in TORPEX simple magnetized plasmas using high resolution diagnostics, control parameters, linear fluid models and nonlinear numerical simulations. The nature of the dominant instabilities is controlled by the ratio between vertical and toroidal magnetic field intensities. For Bv/BT>3%, only ideal interchange instabilities are observed. A critical pressure gradient to drive the interchange instability is experimentally identified. Interchange modes give rise to blobs, radially propagating filaments of enhanced plasma pressure. The measured values of blob velocities and sizes span a wide range and are described by a single analytical expression, from the small blob size regime in which the blob velocity is limited by cross-field ion polarization currents, to the large blob size regime in which the limitation to the blob velocity comes from parallel currents to the sheath. As a first attempt at controlling the blob dynamical properties, limiter configurations with varying angles between field lines and the conducting surface of the limiter are explored. Mach probe measurements clearly demonstrate a link between toroidal flows and blobs. To complement probe data, a fast framing camera and a movable gas puffing system are installed. Density and light fluctuations show similar signatures of interchange activity, but the fast camera images can be obtained with higher spatial resolution, proving data on small turbulence scales. The effect of interchange turbulence on fast ion phase space dynamics is studied using movable fast ion source and detector. A theory validation project is conducted in conjunction with TORPEX experiments, based on quantitative comparisons of observables that are defined in the same way in the data and in 2D and 3D local and global simulations.
GYPW01 23rd July 2010
11:30 to 12:15
P Helander Rotation and zonal flows in stellarators
GYPW01 23rd July 2010
14:00 to 14:45
Effects of three-dimensional geometry and radial electric field on ITG turbulence and zonal flows
GYPW01 23rd July 2010
15:00 to 15:30
Workshop Summary
GYP 26th July 2010
09:00 to 09:40
Recent progress and future outlook for kinetic simulations of magnetic reconnection
GYP 26th July 2010
10:00 to 10:40
Particle acceleration and the role of pressure anisotropy in a multi-island reconnection
GYP 26th July 2010
11:30 to 12:10
The equations of state in collisionless reconnection and their implications for the electron diffusion region
Wind and Cluster spacecraft observations of reconnecting current sheets in the Earth`s magnetotail show strong electron temperature anisotropy. This anisotropy is accounted for in a solution of the Vlasov equation that was recently derived for general reconnection geometries with magnetized electrons in the limit of fast transit time [1]. A necessary ingredient is a parallel electric field structure, which maintains quasi-neutrality by regulating the electron density, traps a large fraction of thermal electrons, and heats electrons in the parallel direction. Based on the expression for the electron phase space density, equations of state provide a fluid closure that relates the parallel and perpendicular pressures to the density and magnetic field strength [2]. This new fluid model agrees well with fully kinetic simulations of guide-field reconnection, where the parallel electron temperature becomes many times greater than the perpendicular temperature. In addition, the equations of state relate features of the electron diffusion region that develop during anti-parallel reconnection to the upstream electron beta. They impose strong constraints on the electron Hall currents and magnetic fields [3]. For plasmas with low electron beta gradients in the anisotropic pressure can support large parallel electric fields over extended regions. This is likely important for energization of super-thermal electrons in the Earth magnetotail [4] and perhaps also for fast electrons observed during reconnection events at the sun. [1] J. Egedal, N. Katz, et al., J. Geophys. Res. 113, A12207 (2008). [2] A. Le, J. Egedal, et al., Phys. Rev. Lett., 102, 085001 (2009). [3] A. Le, J. Egedal, et al., Geophys. Res. Lett. 37, L03106 (2010). [4] J. Egedal, A. Le, et al., Geophys. Res. Lett. In press (2010).
GYP 26th July 2010
14:00 to 14:40
B Rogers Gyrokinetic simulations of reconnection - an update
GYP 27th July 2010
10:00 to 11:30
S Nazarenko Inverse cascades, zonal jets and turbulence/transport suppression in CHM model
GYP 27th July 2010
11:30 to 12:30
Gyrokinetic Simulations of Solar Wind Turbulence and its Dissipation: Importance of Nonlocal Effects on the Energy Cascade
GYP 27th July 2010
14:00 to 15:00
P Catto Some things (we think) we have learned about pedestals
GYP 27th July 2010
15:15 to 15:45
P Helander Electric field effects in stellarators
GYP 27th July 2010
16:30 to 17:00
Gyrokinetics in the pedestal
GYP 27th July 2010
17:15 to 17:45
What sets the residual electron heat transport in an edge transport barrier?
GYP 28th July 2010
10:00 to 11:30
Breaking field lines during reconnection: it's anomalous viscosity not anomalous resistivity
GYP 28th July 2010
14:00 to 15:00
H Wilson Non-linear kinetic theory of drift-tearing modes in magnetised plasmas
GYP 28th July 2010
15:00 to 16:00
P Dorland Mediated round-table discussion on microtearing challenges
Discussion on the microtearing challenge using Colin Roach's (Culham) slides from a talk in Vienna on microtearing studies.
GYP 29th July 2010
09:00 to 09:40
D Schaffner Turbulence and flow in the Large Plasma Device
GYP 29th July 2010
10:00 to 10:40
B Rogers Pinch regimes in gyrokinetic simulations of closed fieldline systems and turbulent transport in LAPD
GYP 29th July 2010
11:30 to 12:10
Gyrokinetic modeling for basic turbulence experiments on the LAPD
We describe our gyrokinetic modeling efforts in support of planned basic turbulence experiments on the LAPD at UCLA. The focal point of this investigation is the fundamental building block of Alfvenic turbulence, the nonlinear interaction between two counter-propagating Alfven waves. Although the frequencies of Alfvenic fluctuations under typical LAPD operating parameters are often a substantial fraction (sometimes half or more) of the ion cyclotron frequency, our initial investigation has demonstrated that corrections to the predictions of the plasma behavior using gyrokinetics due to cyclotron effects are typically less than 10%. The intermediate collisionality of the LAPD plasma yields a much greater effect on the plasma dynamics and dissipation, yet a newly developed collision operator that has been implemented in the Astrophysical Gyrokinetics code AstroGK recovers the correct behavior in this challenging limit. I will describe current efforts underway to model the amplitude dependence of the nonlinear energy transfer rate; these results will help guide the design of the experiments to be performed in the laboratory.
GYP 29th July 2010
14:00 to 14:40
Experiments on the Propagation of Plasma Filaments in VTF
We investigate experimentally the motion and structure of isolated plasma filaments propagating through neutral gas. Plasma filaments, or "blobs," arise from turbulent fluctuations in a range of plasmas. Our experimental geometry is toroidally symmetric, and the blobs expand to a larger major radius under the influence of a vertical electric field. The electric field, which is caused by ÑB and curvature drifts in a 1/R magnetic field, is limited by collisional damping on the neutral gas. The blob's electrostatic potential structure and the resulting E×B flow field give rise to a vortex pair and a mushroom shape, which are consistent with nonlinear plasma simulations. We observe experimentally this characteristic mushroom shape. We also find that the blob propagation velocity is inversely proportional to the neutral density and decreases with time as the blob cools [1]. [1] Katz N, Egedal J, et al, (2008) Phys. Rev. Lett. 101, 015003.
GYP 29th July 2010
15:00 to 15:40
The simulation effort for the basic plasma physics experiment TORPEX
TORPEX is a toroidal device in which a vertical magnetic field superposed on a toroidal field creates helicoidal field lines with both ends terminating on the torus vessel. As in the scrape-off layer of magnetic fusion device, the plasma turbulence driven by magnetic curvature and plasma gradients causes plasma transport in the radial direction while at the same time it is progressively lost due to flows along the field lines. The configuration facilitates the experimental study of low frequency instabilities and related transport, as it allows more detailed experimental diagnostics and wider parameter scans than are usually possible in fusion devices. The relatively simple magnetic geometry of the TORPEX configuration also enables deep theoretical investigations, analytical development, and makes an accurate comparison between simulations and experiments possible. Recently, a three-dimensional global fluid code that solves the drift-reduced Braginskii equations in the whole TORPEX domain has been developed, taking into account the plasma source, plasma losses at the torus vessel, and the plasma turbulent dynamics. We show simulation results and their physical interpretation across a wide parameter space; in particular, we point out that three turbulent regimes exist, which are driven respectively by the ideal interchange mode, by the resistive interchange mode, and by drift waves. Comparison with experimental results is discussed, showing that the predicted turbulence regime transitions are in agreement with the experimental observations.
GYP 29th July 2010
16:30 to 16:50
Theory and modeling in simplified magnetic configurations
GYP 29th July 2010
17:00 to 17:40
2D and 3D kinetic simulations of the MRX reconnection experiment
GYP 30th July 2010
09:30 to 10:30
The diffusion region in collisionless magnetic reconnection: New results from in-situ space observations in the Earth's magnetotail
GYP 2nd August 2010
10:00 to 11:00
Gyrokinetic energy conservation laws
GYP 2nd August 2010
14:00 to 14:45
Entropy transfer processes in kinetic plasma turbulence and zonal flows
GYP 2nd August 2010
15:00 to 15:45
Gyrokinetic Phase-space Turbulence and Energy Flows: Review, Progress and Open Problems
GYP 3rd August 2010
10:00 to 11:00
Energy flows and entropy balance in multiscale gyrokinetics
GYP 3rd August 2010
14:00 to 15:00
An Introduction to CodeRunner
GYP 4th August 2010
10:00 to 11:00
Lagrangian chaos and the evolution of advected fields
GYP 4th August 2010
14:00 to 15:00
A Mishchenko Gyrokinetic particle-in-cell simulations of Alfvenic modes
GYP 5th August 2010
10:00 to 11:00
S Balbus MHD instabilites in dilute astrophysical plasmas
GYP 5th August 2010
14:00 to 15:00
M Kunz Viscous instabilities in weakly collisional astrophysical discs
GYP 5th August 2010
15:30 to 16:30
Gyrofluid momentum conservation law
GYP 6th August 2010
10:00 to 11:00
Gyrokinetic statistical absolute equilibrium and turbulence
GYP 9th August 2010
10:00 to 11:00
S Cowley Shape matters
GYP 9th August 2010
14:00 to 15:00
Lattice Boltzmann approaches for magnetohydrodynamics and related models
GYP 10th August 2010
10:00 to 11:00
Global Gyrokinetic Equations: Extended Orderings and Second Order Terms
GYP 10th August 2010
11:00 to 11:40
S Leerink Full f Gyrokinetic Simulation of Tokamak Plasma Turbulence using ELMFIRE
GYP 10th August 2010
14:00 to 14:40
I Calvo Lagrangian formulation of gyrokinetic theory with a single expansion parameter
GYP 10th August 2010
15:00 to 15:40
F Parra Radial electric field in full-f gyrokinetic simulations
GYP 11th August 2010
10:00 to 11:00
M Vittot Intrinsic guiding-center dynamics: towards gyro-center reduction in Maxwell-Vlasov algebra
GYP 11th August 2010
14:00 to 15:00
Subcritical fluctuations in a differentially rotating gyrokinetic plasma: linear theory
GYP 12th August 2010
10:00 to 11:00
A Mishchenko Non-linear correction to the gyrokinetic polarization density
GYP 12th August 2010
14:00 to 15:00
Programme summary and mediated discussion of the outstanding questions/future directions
University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons