Search Results - (Author, Cooperation:J. F. Drake)
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1Latest Papers from Table of Contents or Articles in PressO. Agapitov, J. F. Drake, I. Vasko, F. S. Mozer, A. Artemyev, V. Krasnoselskikh, V. Angelopoulos, J. Wygant, G. D. Reeves
Wiley-Blackwell
Published 2018Staff ViewPublication Date: 2018-03-06Publisher: Wiley-BlackwellPrint ISSN: 0094-8276Electronic ISSN: 1944-8007Topics: GeosciencesPhysicsPublished by: -
2Latest Papers from Table of Contents or Articles in PressG. T. Roberg-Clark, J. F. Drake, C. S. Reynolds, and M. Swisdak
American Physical Society (APS)
Published 2018Staff ViewPublication Date: 2018-01-20Publisher: American Physical Society (APS)Print ISSN: 0031-9007Electronic ISSN: 1079-7114Topics: PhysicsKeywords: Plasma and Beam PhysicsPublished by: -
3Latest Papers from Table of Contents or Articles in PressStaff View
Publication Date: 2018-01-30Publisher: Wiley-BlackwellPrint ISSN: 0094-8276Electronic ISSN: 1944-8007Topics: GeosciencesPhysicsPublished by: -
4Latest Papers from Table of Contents or Articles in PressJ. L. Burch ; R. B. Torbert ; T. D. Phan ; L. J. Chen ; T. E. Moore ; R. E. Ergun ; J. P. Eastwood ; D. J. Gershman ; P. A. Cassak ; M. R. Argall ; S. Wang ; M. Hesse ; C. J. Pollock ; B. L. Giles ; R. Nakamura ; B. H. Mauk ; S. A. Fuselier ; C. T. Russell ; R. J. Strangeway ; J. F. Drake ; M. A. Shay ; Y. V. Khotyaintsev ; P. A. Lindqvist ; G. Marklund ; F. D. Wilder ; D. T. Young ; K. Torkar ; J. Goldstein ; J. C. Dorelli ; L. A. Avanov ; M. Oka ; D. N. Baker ; A. N. Jaynes ; K. A. Goodrich ; I. J. Cohen ; D. L. Turner ; J. F. Fennell ; J. B. Blake ; J. Clemmons ; M. Goldman ; D. Newman ; S. M. Petrinec ; K. J. Trattner ; B. Lavraud ; P. H. Reiff ; W. Baumjohann ; W. Magnes ; M. Steller ; W. Lewis ; Y. Saito ; V. Coffey ; M. Chandler
American Association for the Advancement of Science (AAAS)
Published 2016Staff ViewPublication Date: 2016-05-14Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsPublished by: -
5Latest Papers from Table of Contents or Articles in PressStaff View
Publication Date: 2011-06-03Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsPublished by: -
6Latest Papers from Table of Contents or Articles in PressStaff View
Publication Date: 2018-12-21Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyGeosciencesComputer ScienceMedicineNatural Sciences in GeneralPhysicsKeywords: Geochemistry, Geophysics, Physics, Planetary SciencePublished by: -
7Articles: DFG German National LicensesAntonsen, T. M. ; Drake, J. F. ; Guzdar, P. N. ; Hassam, A. B. ; Lau, Y. T. ; Liu, C. S. ; Novakovskii, S. V.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The enhancement of stability to ballooning modes from negative shear in tokamaks is shown to be a simple consequence of the orientation of the convective cell with respect to the toroidally outward effective gravity, g↘. For modest positive shear, convective cells remain oriented along g↘ as they map along field lines. In contrast, for negative shear or very positive shear convective cells twist strongly away from g↘ and are less strongly driven. The twist of convection cells is controlled by the profile of the vertical magnetic field along the outer midplane, Bz. Twist is a minimum in regions where Bz is independent of the major radius. Transport should be highest in such locations. Resistive ballooning modes in the tokamak edge are strongly stabilized by modest values of negative shear. Tokamak discharges with finite values of βp develop regions of local negative shear on the outside midplane of the plasma torus. This local negative shear should self-stabilize resistive ballooning modes at finite values of the poloidal beta. This effect may impact the transition to high confinement operation (H-mode). © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The self-consistent nonlinear evolution and saturation of the dynamo, including the back reaction of the magnetic field on the flow through the Lorentz J×B force, is investigated via simulation of the fully compressible magnetohydrodynamic (MHD) equations. The saturated state is found to be highly turbulent. The energy in the saturated magnetic field is only a small fraction of the kinetic energy in the flow which drives the dynamo. However, as the collision frequency decreases and the Reynolds number R increases, the ratio of magnetic to kinetic energy in the saturated state increases gradually. The nonlinear viscosity generated by the turbulent fluctuations rises rapidly relative to the collisional viscosity as R increases, such that the total transport of momentum remains virtually unchanged as the collisional viscosity is reduced. The scale lengths of the magnetic and velocity fluctuations both decrease as R increases, so that the scale size of the magnetic field remains comparable to the scale size of the flow. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesHassam, A. B. ; Drake, J. F. ; Goel, Deepak ; Lathrop, D. P.
[S.l.] : American Institute of Physics (AIP)
Published 2000Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: A stationary equilibrium of a liquid metal flowing past a cylindrical magnetic cavity is presented. The cavity has an azimuthal magnetic field and can also have an axial field. The liquid metal flow can be maintained by a sufficiently high pressure head. The scheme could be used to support a flowing liquid wall for systems producing high heat fluxes. © 2000 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesZeiler, A. ; Biskamp, D. ; Drake, J. F. ; Guzdar, P. N.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Three-dimensional (3-D) simulations of drift-resistive ballooning turbulence are presented. The turbulence is basically controlled by a parameter α, the ratio of the drift wave frequency to the ideal ballooning growth rate. If this parameter is small [α≤1, corresponding to Ohmic (OH) or low confinement phase (L-mode) plasmas], the system is dominated by ballooning turbulence, which is strongly peaked at the outside of the torus. If it is large [α≥1, corresponding to high confinement phase (H-mode) plasmas], field line curvature plays a minor role. The turbulence is nonlinearly sustained even if curvature is removed and all modes are linearly stable due to magnetic shear. In the nonlinear regime without curvature the system obeys a different scaling law compared to the low-α regime. The transport scaling is discussed in both regimes and the implications for OH, L-mode, and H-mode transport are discussed. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesNovakovskii, S. V. ; Guzdar, P. N. ; Drake, J. F. ; Liu, C. S.
[S.l.] : American Institute of Physics (AIP)
Published 1995Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Analytical and numerical study of the stability of the resistive ballooning modes (RBM) in the scrape-off layer (SOL) of a tokamak plasma is performed. It is shown that the stability of the RBM is controlled by the two parameters λ=(me/mi)1/2νeiqR/vTe—the "effective strength'' of the Debye sheath current, and mˆ=mL0/a the dimensionless poloidal number, where the characteristic scale L0 is given in the main text as a function of the basic plasma edge parameters. For λ(approximately-greater-than)1 the coupling to the sheath is unimportant and the unstable spectrum is virtually unchanged from that in the closed flux region. For λ〈1 the sheath current has a strong destabilizing influence on long wavelength modes. The general case of arbitrary λ and mˆ is studied numerically and the spectrum of the unstable RBM is found. The influence of the diamagnetic effects is also investigated. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesKleva, Robert G. ; Drake, J. F. ; Waelbroeck, F. L.
[S.l.] : American Institute of Physics (AIP)
Published 1995Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Pressure forces acting on electrons are shown to dramatically alter magnetic field line reconnection in high temperature plasmas. The electron pressure introduces a new physical scale length ρs, the ion gyroradius based on the electron temperature, into the resistive magnetohydrodynamic (MHD) equations. The single dissipation layer of resistive MHD is split into two distinct layers by this effect: a very small inner current layer and a larger flow layer. Unlike resistive MHD, the current layer is microscopic in the outflow, as well as the inflow, direction. As a consequence, the current layer is not unstable to the formation of secondary magnetic islands at low values of resistivity and patchy reconnection does not occur. The absence of a strong current sheet in the outflow region enables the magnetic nozzle controlling the outflow to open up. The magnetic reconnection rate therefore remains large as the resistivity η and ρs become small. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The stability of the tokamak edge pedestal to ballooning modes is addressed using three-dimensional simulations of the Braginskii equations and simple analytic models. The effects of ion diamagnetic drift and the finite radial localization of the pedestal pressure gradient are found to be strongly stabilizing when δ〈δR, where δ is the pedestal half-width and δR∼ρi2/3R1/3 in the center of the pedestal. In this limit, conventional ballooning modes within the pedestal region become stable, and a stability condition is obtained in the two fluid system α/αc〈(4/3)δR/δ (stable) which is much less stringent than that predicted by local magnetohydrodynamic (MHD) theory (α/αc〈1). Given α∼q2Rβ/δ, this condition implies a stability limit on the pedestal β: β〈βc, where βc=(4αc/3q2)δR/R. This limit is due the onset of an ideal pressure driven "surface" instability that depends only on the pressure drop across the pedestal. Near marginal conditions, this mode has a poloidal wavenumber kθ∼1/δR, a radial envelope ∼δR(〉δ), and real frequency ω∼cs/δRR. © 1999 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
14Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Three-dimensional nonlinear simulations of collisional plasma turbulence are presented to model the behavior of the edge region of tokamak discharges. Previous work is extended by including electron temperature fluctuations T˜e. The basic paradigm that turbulence and transport are controlled by resistive ballooning modes in low temperature plasma and nonlinearly driven drift wave turbulence in higher temperature regimes persists in the new system. Parallel thermal conduction strongly suppresses the ability of the electron temperature gradient ∇Te to drive the turbulence and transport everywhere except the very low temperature edge of the resistive ballooning regime. As a consequence, over most of the resistive ballooning regime only the density gradient drives the turbulence and the temperature fluctuations are convected as a passive scalar. In the drift wave regime only the density gradient acts to drive the nonlinear instability and the temperature fluctuations have a relatively strong stabilizing influence on the turbulence due to an enhanced damping of density and potential fluctuations resulting from local electron heating. © 1997 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
15Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Three-dimensional (3-D) nonlinear simulations of collisional drift-wave turbulence are presented. Results for the Hasegawa–Wakatani equations (without magnetic shear) in 3-D are compared to former two-dimensional (2-D) simulations. In contrast to the 2-D system the 3-D situation is completely dominated by a nonlinear drive mechanism. The final state of the system is sensitive to the configuration of the computational grid since the sheared flow develops at the longest scales of the system. When magnetic shear is included, the system is linearly stable but the turbulence is self-sustained by basically the same nonlinear mechanism. Magnetic shear limits the size of the dominant eddies, so the system evolves to a stationary turbulent state independent of the computational box. Finally, it is shown that the level of turbulence in the system with magnetic shear depends sensitively on the size of the effective Larmor radius ρs compared with the characteristic transverse scale length of the eddies. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
16Articles: DFG German National LicensesNovakovskii, S. V. ; Guzdar, P. N. ; Drake, J. F. ; Liu, C. S. ; Waelbroeck, F. L.
[S.l.] : American Institute of Physics (AIP)
Published 1995Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Drift resistive ballooning modes (DRBM) are studied for present-day tokamak edge plasmas. A ballooning equation has been derived for DRBM, corresponding to an "optimal ordering,'' i.e., such a choice of the length and time normalizing units that make the three terms in the vorticity equation to be of the same order. A simple criterion to distinguish strong and weak ballooning regimes for DRBM has been obtained. The DRBM in the strong ballooning regime have been studied and it has been found that they are robustly unstable with an ideal growth rate γ∝cs/(RLn)1/2. The weak ballooning regime also has been studied. It has been found that there exist two different unstable branches in this case. The first one has been identified as a conventional DRBM studied earlier. It has been shown, however, that this solution is stabilized when magnetic shear sˆ=aq'/q is order of 1. The other branch has a stronger ballooning structure compared to the conventional DRBM branch and is localized on the outside of the torus. It is less unstable for a weak shear, but is the only one that is robustly unstable for sˆ∼1. A numerical simulation has shown that this branch matches the strong ballooning solution. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
17Articles: DFG German National LicensesMcCarthy, D. R. ; Drake, J. F. ; Guzdar, P. N.
New York, NY : American Institute of Physics (AIP)
Published 1993Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: The parallel velocity shear instability in an axisymmetric toroidal edge plasma is studied numerically. In the presence of a large asymmetric particle transport and a limiter, sonic parallel flows develop that are peaked at the last closed flux surface. For α=ρsqR/aLv(approximately-greater-than)1, these flows are unstable to axisymmetric modes. The associated turbulence gives order unity fluctuation levels. It is located inside the last closed flux surface (LCFS) and on the inner half of the torus. There is an up–down asymmetry of the turbulence which is due to the diamagnetic drift and poloidal rotation. These results are compared to the experimental results from the Continuous Current Tokamak (CCT) (G. R. Tynan, Ph.D. thesis, 1991).Type of Medium: Electronic ResourceURL: -
18Articles: DFG German National LicensesMcCarthy, D. R. ; Drake, J. F. ; Guzdar, P. N. ; Hassam, A. B.
New York, NY : American Institute of Physics (AIP)
Published 1993Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: The equilibrium and stability of axisymmetric toroidal edge plasma in the presence of an anomalous ballooninglike transport is studied. The equilibrium density evolves so that the transport rate, D⊥/Ln2 equals the sound transit time, cs/πqR. As a result, confinement is coupled to the local sound velocity such that a reduced sound velocity (larger ion mass) leads to improved confinement. A result of the large asymmetric transport is the generation of nearly sonic parallel flows which allow the system to be unstable to the Stringer spin-up instability. For weak magnetic pumping, a large poloidal rotation of order the poloidal sound speed (acs/qR) is driven, forming a localized shear layer. The direction of rotation corresponds to a negative radial electric field in the closed flux region. For strong magnetic pumping the rotation is equal in magnitude and opposite in direction to the ion diamagnetic drift, the neoclassical result. Particle sources localized in poloidal angle can strongly impact the rotation. A source placed between the bottom and the outside of the torus enhances the rotation while the same source placed between the top and the inside retards the rotation. However, a large enough source at the latter location will drive the rotation in the other direction, reversing the sign of the electric field. The implications of the results for understanding Ohmic, L-mode, and H-mode discharges are discussed.Type of Medium: Electronic ResourceURL: -
19Articles: DFG German National LicensesDrake, J. F. ; Guzdar, P. N. ; Dimits, A.
New York, NY : American Institute of Physics (AIP)
Published 1991Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: The anomalous transport of ion thermal energy in a heated plasma slab confined by a uniform, straight magnetic field Bz has been investigated in three-dimensional (3-D) fluid simulations. Convection flows are driven unstable by ∇Ti and nonlinearly develop into narrow streams which carry cold edge plasma into the hot center. The convective flows undergo a sharp transition from laminar to turbulent behavior as the thermal energy confined in the slab is increased beyond a critical level. This transition is reminiscent of similar behavior in Rayleigh–Bénard convection in heated fluids. The convective thermal transport increases sharply as this turbulence threshold is exceeded. The structure of the flow patterns and associated transport also depend strongly on the physical dimensions of the confined plasma (Lx,Ly,Lz) =(a,2πa,2πR) compared with the ion Larmor radius ρi. For α=a2/Rρi〉1, the dominant flows have kyρi ∼a/R and produce an anomalous cross field thermal transport χ⊥i that scales as via2/R . In the opposite limit α=a2/Rρi 〈1, dominant flows have kya∼1 and the transport is given by χ⊥i∼ρivi , the Bohm scaling. Close to marginal stability, the transport is greatly reduced. These simulations imply that ion thermal transport in any straight field system such as a tandem mirror or a stellarator with weak shear and nearly rational fields will be strongly anomalous if the ∇Ti threshold for instability is exceeded.Type of Medium: Electronic ResourceURL: -
20Articles: DFG German National LicensesDrake, J. F. ; Sparks, L. ; Van Hoven, G.
[S.l.] : American Institute of Physics (AIP)
Published 1988Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: The structure and growth rate of the radiative instability in a sheared magnetic field B have been calculated analytically using the Braginskii fluid equations. In a shear layer, temperature and density perturbations are linked by the propagation of sound waves parallel to the local magnetic field. As a consequence, density clumping or condensation plays an important role in driving the instability. Parallel thermal conduction localizes the mode to a narrow layer where k(parallel) =k⋅B/||B|| is small and stabilizes short wavelengths k〉kc, where kc depends on the local radiation and conduction rates. Thermal coupling to ions also limits the width of the unstable spectrum. It is shown that a broad spectrum of modes is typically unstable in tokamak edge plasmas and it is argued that this instability is sufficiently robust to drive the large-amplitude density fluctuations often measured there.Type of Medium: Electronic ResourceURL: