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Seminars (GYPW01)

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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
University of Cambridge Research Councils UK
    Clay Mathematics Institute London Mathematical Society NM Rothschild and Sons