159 results found
Henneberg SA, Cowley SC, Wilson HR, 2018, Filamentary plasma eruptions: Results using the non-linear ballooning model, Contributions to Plasma Physics, Vol: 58, Pages: 6-20, ISSN: 0863-1042
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim This paper provides an overview of recent results on two distinct studies exploiting the non-linear model for ideal ballooning modes with potential applications to edge-localized modes (ELMs). The non-linear model for tokamak geometries was developed by Wilson and Cowley in 2004 and consists of two differential equations that characterize the temporal and spatial evolution of the plasma displacement. The variation of the radial displacement along the magnetic field line is described by the first equation, which is identical to the linear ballooning equation. The second differential equation is a two-dimensional non-linear ballooning-like equation, which is often second order in time but can involve a fractional time derivative depending on the geometry. In the first study, the interaction of multiple filamentary eruptions is addressed in a magnetized plasma in a slab geometry. Equally sized filaments evolve independently in both the linear and non-linear regimes. However, if filaments are initiated with slightly different heights from the reference flux surface, they interact with each other in the non-linear regime: lower filaments are slowed down and are eventually completely suppressed, while the higher filaments grow faster because of the non-linear interaction. In the second study, this model of non-linear ballooning modes is examined quantitatively against experimental observations of ELMs in Mega Amp Spherical Tokamak (MAST) geometries. The results suggest that experimentally relevant results can only be obtained using modified equilibria.
Cowley SC, 2016, The quest for fusion power, NATURE PHYSICS, Vol: 12, Pages: 384-386, ISSN: 1745-2473
Ham CJ, Cowley SC, Brochard G, et al., 2016, Explosive Ballooning Flux Tubes in Tokamaks
Tokamak stability to, potentially explosive, `ballooning' displacements ofelliptical magnetic flux tubes is examined in large aspect ratio equilibrium.Above a critical pressure gradient the energy stored in the plasma may belowered by finite (but not infinitesimal) displacements of such tubes(metastability). Above a higher pressure gradient, the linear stabilityboundary, such tubes are linearly and nonlinearly unstable. The flux tubedisplacement can be of the order of the pressure gradient scale length. Plasmatransport from displaced flux tubes may result in rapid loss of confinement.
Ham CJ, Cowley SC, Brochard G, et al., 2016, Nonlinear Stability and Saturation of Ballooning Modes in Tokamaks, PHYSICAL REVIEW LETTERS, Vol: 116, ISSN: 0031-9007
Cowley SC, Cowley B, Henneberg SA, et al., 2015, Explosive instability and erupting flux tubes in a magnetized plasma, PROCEEDINGS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 471, ISSN: 1364-5021
Henneberg SA, Cowley SC, Wilson HR, 2015, Interacting filamentary eruptions in magnetised plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 57, ISSN: 0741-3335
Kunz MW, Schekochihin AA, Chen CHK, et al., 2015, Inertial-range kinetic turbulence in pressure-anisotropic astrophysical plasmas, JOURNAL OF PLASMA PHYSICS, Vol: 81, ISSN: 0022-3778
Rincon F, Schekochihin AA, Cowley SC, 2015, Non-linear mirror instability, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 447, Pages: L45-L49, ISSN: 0035-8711
Cole MDJ, Newton SL, Cowley SC, et al., 2014, Electromagnetic effects in the stabilization of turbulence by sheared flow, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 56, ISSN: 0741-3335
Abel IG, Cowley SC, 2013, Multiscale gyrokinetics for rotating tokamak plasmas: II. Reduced models for electron dynamics, NEW JOURNAL OF PHYSICS, Vol: 15, ISSN: 1367-2630
Abel IG, Plunk GG, Wang E, et al., 2013, Multiscale gyrokinetics for rotating tokamak plasmas: fluctuations, transport and energy flows, REPORTS ON PROGRESS IN PHYSICS, Vol: 76, ISSN: 0034-4885
Ghim Y-C, Schekochihin AA, Field AR, et al., 2013, Experimental Signatures of Critically Balanced Turbulence in MAST, PHYSICAL REVIEW LETTERS, Vol: 110, ISSN: 0031-9007
Ham CJ, Connor JW, Cowley SC, et al., 2013, The role of pressure flattening in calculating tearing mode stability, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 55, ISSN: 0741-3335
Meyer H, Abel IG, Akers RJ, et al., 2013, Overview of physics results from MAST towards ITER/DEMO and the MAST Upgrade, NUCLEAR FUSION, Vol: 53, ISSN: 0029-5515
Schekochihin AA, Highcock EG, Cowley SC, 2012, Subcritical fluctuations and suppression of turbulence in differentially rotating gyrokinetic plasmas, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 54, ISSN: 0741-3335
Barnes M, Parra FI, Highcock EG, et al., 2011, Turbulent Transport in Tokamak Plasmas with Rotational Shear, PHYSICAL REVIEW LETTERS, Vol: 106, ISSN: 0031-9007
Highcock EG, Barnes M, Parra FI, et al., 2011, Transport bifurcation induced by sheared toroidal flow in tokamak plasmas, PHYSICS OF PLASMAS, Vol: 18, ISSN: 1070-664X
Kunz MW, Schekochihin AA, Cowley SC, et al., 2011, A thermally stable heating mechanism for the intracluster medium: turbulence, magnetic fields and plasma instabilities, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 410, Pages: 2446-2457, ISSN: 0035-8711
Parra FI, Barnes M, Highcock EG, et al., 2011, Momentum Injection in Tokamak Plasmas and Transitions to Reduced Transport, PHYSICAL REVIEW LETTERS, Vol: 106, ISSN: 0031-9007
Rosin MS, Schekochihin AA, Rincon F, et al., 2011, A non-linear theory of the parallel firehose and gyrothermal instabilities in a weakly collisional plasma, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 413, Pages: 7-38, ISSN: 0035-8711
Schekochihin AA, Highcock EG, Cowley SC, 2011, Suppression of turbulence and subcritical fluctuations in differentially rotating gyrokinetic plasmas, PPCF, Vol: 54
Differential rotation is known to suppress linear instabilities in fusionplasmas. However, even in the absence of growing eigenmodes, subcriticalfluctuations that grow transiently can lead to sustained turbulence. Heretransient growth of electrostatic fluctuations driven by the parallel velocitygradient (PVG) and the ion temperature gradient (ITG) in the presence of aperpendicular ExB velocity shear is considered. The maximally simplified caseof zero magnetic shear is treated in the framework of a local shearing box.There are no linearly growing eigenmodes, so all excitations are transient. Themaximal amplification factor of initial perturbations and the correspondingwavenumbers are calculated as functions of q/\epsilon (=safety factor/aspectratio), temperature gradient and velocity shear. Analytical results arecorroborated and supplemented by linear gyrokinetic numerical tests. Forsufficiently low values of q/\epsilon (<7 in our model), regimes with fullysuppressed ion-scale turbulence are possible. For cases when turbulence is notsuppressed, an elementary heuristic theory of subcritical PVG turbulenceleading to a scaling of the associated ion heat flux with q, \epsilon, velocityshear and temperature gradient is proposed; it is argued that the transport ismuch less stiff than in the ITG regime.
Brown B, Forest C, Nornberg M, et al., 2010, An Experimental Plasma Dynamo Program for Investigations of Fundamental Processes in Heliophysics
Plasma experiments in laboratory settings offer unique opportunities toaddress fundamental aspects of the solar dynamo and magnetism in the solaratmosphere. We argue here that ground-based laboratory experiments have directconnections to NASA based missions and NSF programs, and that a smallinvestment in laboratory heliophysics may have a high payoff. We advocate forbroad involvement in community-scale plasma experiments.
Cowley S, 2010, Hot fusion, PHYSICS WORLD, Vol: 23, Pages: 46-51, ISSN: 0953-8585
Highcock EG, Barnes M, Schekochihin AA, et al., 2010, Transport Bifurcation in a Rotating Tokamak Plasma, PHYSICAL REVIEW LETTERS, Vol: 105, ISSN: 0031-9007
Newton SL, Cowley SC, Loureiro NF, 2010, Understanding the effect of sheared flow on microinstabilities, PLASMA PHYSICS AND CONTROLLED FUSION, Vol: 52, ISSN: 0741-3335
Schekochihin AA, Cowley SC, Rincon F, et al., 2010, Magnetofluid dynamics of magnetized cosmic plasma: firehose and gyrothermal instabilities, MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Vol: 405, Pages: 291-300, ISSN: 0035-8711
Smith CL, Cowley S, 2010, The path to fusion power, PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY A-MATHEMATICAL PHYSICAL AND ENGINEERING SCIENCES, Vol: 368, Pages: 1091-1108, ISSN: 1364-503X
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