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  • AIP Publishing  (51)
  • 1
    Online Resource
    Online Resource
    Review of deuterium–tritium results from the Tokamak Fusion Test Reactor
    AIP Publishing ; 1995
    In:  Physics of Plasmas Vol. 2, No. 6 ( 1995-06-01), p. 2176-2188
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 2, No. 6 ( 1995-06-01), p. 2176-2188
    Abstract: After many years of fusion research, the conditions needed for a D–T fusion reactor have been approached on the Tokamak Fusion Test Reactor (TFTR) [Fusion Technol. 21, 1324 (1992)]. For the first time the unique phenomena present in a D–T plasma are now being studied in a laboratory plasma. The first magnetic fusion experiments to study plasmas using nearly equal concentrations of deuterium and tritium have been carried out on TFTR. At present the maximum fusion power of 10.7 MW, using 39.5 MW of neutral-beam heating, in a supershot discharge and 6.7 MW in a high-βp discharge following a current rampdown. The fusion power density in a core of the plasma is ≊2.8 MW m−3, exceeding that expected in the International Thermonuclear Experimental Reactor (ITER) [Plasma Physics and Controlled Nuclear Fusion Research (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 239] at 1500 MW total fusion power. The energy confinement time, τE, is observed to increase in D–T, relative to D plasmas, by 20% and the ni(0) Ti(0) τE product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter-H-mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high-βp discharges. Ion cyclotron range of frequencies (ICRF) heating of a D–T plasma, using the second harmonic of tritium, has been demonstrated. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP [Nucl. Fusion 34, 1247 (1994)] simulations. Initial measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from He gas puffing experiments. The loss of alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha-particle-driven instabilities has yet been observed. D–T experiments on TFTR will continue to explore the assumptions of the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.871303
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1995
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  • 2
    Online Resource
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    Fusion plasma experiments on TFTR: A 20 year retrospective
    AIP Publishing ; 1998
    In:  Physics of Plasmas Vol. 5, No. 5 ( 1998-05-01), p. 1577-1589
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 5, No. 5 ( 1998-05-01), p. 1577-1589
    Abstract: The Tokamak Fusion Test Reactor (TFTR) (R. J. Hawryluk, to be published in Rev. Mod. Phys.) experiments on high-temperature plasmas, that culminated in the study of deuterium–tritium D–T plasmas containing significant populations of energetic alpha particles, spanned over two decades from conception to completion. During the design of TFTR, the key physics issues were magnetohydrodynamic (MHD) equilibrium and stability, plasma energy transport, impurity effects, and plasma reactivity. Energetic particle physics was given less attention during this phase because, in part, of the necessity to address the issues that would create the conditions for the study of energetic particles and also the lack of diagnostics to study the energetic particles in detail. The worldwide tokamak program including the contributions from TFTR made substantial progress during the past two decades in addressing the fundamental issues affecting the performance of high-temperature plasmas and the behavior of energetic particles. The progress has been the result of the construction of new facilities, which enabled the production of high-temperature well-confined plasmas, development of sophisticated diagnostic techniques to study both the background plasma and the resulting energetic fusion products, and computational techniques to both interpret the experimental results and to predict the outcome of experiments.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.872825
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1998
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  • 3
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    Deuterium–tritium plasmas in novel regimes in the Tokamak Fusion Test Reactor
    AIP Publishing ; 1997
    In:  Physics of Plasmas Vol. 4, No. 5 ( 1997-05-01), p. 1714-1724
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 4, No. 5 ( 1997-05-01), p. 1714-1724
    Abstract: Experiments in the Tokamak Fusion Test Reactor (TFTR) [Phys. Plasmas 2, 2176 (1995)] have explored several novel regimes of improved tokamak confinement in deuterium–tritium (D–T) plasmas, including plasmas with reduced or reversed magnetic shear in the core and high-current plasmas with increased shear in the outer region (high li). New techniques have also been developed to enhance the confinement in these regimes by modifying the plasma-limiter interaction through in situ deposition of lithium. In reversed-shear plasmas, transitions to enhanced confinement have been observed at plasma currents up to 2.2 MA (qa≈4.3), accompanied by the formation of internal transport barriers, where large radial gradients develop in the temperature and density profiles. Experiments have been performed to elucidate the mechanism of the barrier formation and its relationship with the magnetic configuration and with the heating characteristics. The increased stability of high-current, high-li plasmas produced by rapid expansion of the minor cross section, coupled with improvement in the confinement by lithium deposition has enabled the achievement of high fusion power, up to 8.7 MW, with D–T neutral beam heating. The physics of fusion alpha-particle confinement has been investigated in these regimes, including the interactions of the alphas with endogenous plasma instabilities and externally applied waves in the ion cyclotron range of frequencies. In D–T plasmas with q0 & gt;1 and weak magnetic shear in the central region, a toroidal Alfvén eigenmode instability driven purely by the alpha particles has been observed for the first time. The interactions of energetic ions with ion Bernstein waves produced by mode conversion from fast waves in mixed-species plasmas have been studied as a possible mechanism for transferring the energy of the alphas to fuel ions.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.872274
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1997
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  • 4
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    Comparisons of gyrofluid and gyrokinetic simulations*
    AIP Publishing ; 1994
    In:  Physics of Plasmas Vol. 1, No. 5 ( 1994-05-01), p. 1461-1468
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 1, No. 5 ( 1994-05-01), p. 1461-1468
    Abstract: The gyrokinetic and gyrofluid models show the most promise for large scale simulations of tokamak microturbulence. This paper discusses detailed comparisons of these two complementary approaches. Past comparisons with linear theory have been fairly good, therefore the emphasis here is on nonlinear comparisons. Simulations include simple two-dimensional slab test cases, turbulent three-dimensional slab cases, and toroidal cases, each modeling the nonlinear evolution of the ion temperature gradient instability. There is good agreement in both turbulent and coherent nonlinear slab comparisons in terms of the ion heat flux, both in magnitude and scaling with magnetic shear. However, the nonlinear saturation level for ‖Φ‖ in the slab comparisons shows differences of approximately 40%. Preliminary toroidal comparisons show agreement within 50%, in terms of ion heat flux and saturation level.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.870696
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1994
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  • 5
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    Online Resource
    Simulating gyrokinetic microinstabilities in stellarator geometry with GS2
    AIP Publishing ; 2011
    In:  Physics of Plasmas Vol. 18, No. 12 ( 2011-12-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 18, No. 12 ( 2011-12-01)
    Abstract: The nonlinear gyrokinetic code GS2 has been extended to treat non-axisymmetric stellarator geometry. Electromagnetic perturbations and multiple trapped particle regions are allowed. Here, linear, collisionless, electrostatic simulations of the quasi-axisymmetric, three-field period national compact stellarator experiment (NCSX) design QAS3-C82 have been successfully benchmarked against the eigenvalue code FULL. Quantitatively, the linear stability calculations of GS2 and FULL agree to within ∼10%.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.3662064
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2011
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  • 6
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    Fluid models of phase mixing, Landau damping, and nonlinear gyrokinetic dynamics
    AIP Publishing ; 1992
    In:  Physics of Fluids B: Plasma Physics Vol. 4, No. 7 ( 1992-07-01), p. 2052-2061
    Details
    In: Physics of Fluids B: Plasma Physics, AIP Publishing, Vol. 4, No. 7 ( 1992-07-01), p. 2052-2061
    Abstract: Fluidlike models have long been used to develop qualitative understanding of the drift-wave class of instabilities (such as the ion temperature gradient mode and various trapped-particle modes) which are prime candidates for explaining anomalous transport in plasmas. Here, the fluid approach is improved by developing fairly realistic models of kinetic effects, such as Landau damping and gyroradius orbit averaging, which strongly affect both the linear mode properties and the resulting nonlinear turbulence. Central to this work is a simple but effective fluid model [Phys. Rev. Lett. 64, 3019 (1990)] of the collisionless phase mixing responsible for Landau damping (and inverse Landau damping). This model is based on a nonlocal damping term with a damping rate ∼ vt‖k∥‖ in the closure approximation for the nth velocity space moment of the distribution function f, resulting in an n-pole approximation of the plasma dispersion function Z. Alternatively, this closure approximation is linearly exact (and therefore physically realizable) for a particular f0 which is close to Maxwellian. ‘‘Gyrofluid’’ equations (conservation laws for the guiding-center density n, momentum mnu∥, and parallel and perpendicular pressures p∥ and p⊥) are derived by taking moments of the gyrokinetic equation in guiding-center coordinates rather than particle coordinates. This naturally yields nonlinear gyroradius terms and an important gyroaveraging of the shear. The gyroradius effects in the Bessel functions are modeled with robust Padé-like approximations. These new fluid models of phase mixing and Landau damping are being applied by others to a broad range of applications outside of drift-wave turbulence, including strong Langmuir turbulence, laser–plasma interactions, and the α-driven toroidicity-induced Alfvén eigenmode (TAE) instability.
    Type of Medium: Online Resource
    ISSN: 0899-8221
    URL: Article
    DOI: 10.1063/1.860014
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1992
    detail.hit.zdb_id: 2130787-8
    detail.hit.zdb_id: 648023-8
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  • 7
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    Discrete particle noise in particle-in-cell simulations of plasma microturbulence
    AIP Publishing ; 2005
    In:  Physics of Plasmas Vol. 12, No. 12 ( 2005-12-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 12, No. 12 ( 2005-12-01)
    Abstract: Recent gyrokinetic simulations of electron temperature gradient (ETG) turbulence with the global particle-in-cell (PIC) code GTC [Z. Lin et al., Proceedings of the 20th Fusion Energy Conference, Vilamoura, Portugal, 2004 (IAEA, Vienna, 2005)] yielded different results from earlier flux-tube continuum code simulations [F. Jenko and W. Dorland, Phys. Rev. Lett. 89, 225001 (2002)] despite similar plasma parameters. Differences between the simulation results were attributed to insufficient phase-space resolution and novel physics associated with global simulation models. The results of the global PIC code are reproduced here using the flux-tube PIC code PG3EQ [A. M. Dimits et al., Phys. Rev. Lett. 77, 71 (1996)], thereby eliminating global effects as the cause of the discrepancy. The late-time decay of the ETG turbulence and the steady-state heat transport observed in these PIC simulations are shown to result from discrete particle noise. Discrete particle noise is a numerical artifact, so both these PG3EQ simulations and, by inference, the GTC simulations that they reproduced have little to say about steady-state ETG turbulence and the associated anomalous heat transport. In the course of this work several diagnostics are developed to retrospectively test whether a particular PIC simulation is dominated by discrete particle noise.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.2118729
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2005
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  • 8
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    Online Resource
    Role of stable eigenmodes in gyrokinetic models of ion temperature gradient turbulence
    AIP Publishing ; 2009
    In:  Physics of Plasmas Vol. 16, No. 2 ( 2009-02-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 16, No. 2 ( 2009-02-01)
    Abstract: Investigation of ion temperature gradient turbulence in gyrokinetic models shows that some of the key features of reduced models associated with saturation by nonlinearly excited damped eigenmodes carry over to gyrokinetics. For nonzonal wavenumbers the frequency spectrum in gyrokinetics is broader by a factor of 10 than simple nonlinear broadening of the most unstable eigenmode. The width, including its variations with wavenumber and temperature gradient scale length, closely tracks accessible stable eigenmodes as approximated by a gyro-Landau fluid model for the same parameters. Cross-phase probability distribution functions (pdfs) and fluxes show nonlinear behavior consistent with stable eigenmodes in nonzonal wavenumbers contributing to 30% of the fluctuation energy. Phase pdfs and cross-phase time histories show that multiple eigenmodes [in addition to high frequency geodesic acoustic modes (GAMs)] are a significant part of the ky=0 spectrum. Two possible roles of zonal modes in saturation are proposed. First, known nonlinearly accessible stable zonal eigenmodes (in addition to zonal flows and GAMs) are discussed and it is suggested that if these eigenmodes are excited they may be the primary arbiter of saturation. Second, zonal modes may facilitate energy transfer from unstable eigenmodes to stable eigenmodes at finite ky.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.3079779
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2009
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  • 9
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    Comparisons and physics basis of tokamak transport models and turbulence simulations
    AIP Publishing ; 2000
    In:  Physics of Plasmas Vol. 7, No. 3 ( 2000-03-01), p. 969-983
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 7, No. 3 ( 2000-03-01), p. 969-983
    Abstract: The predictions of gyrokinetic and gyrofluid simulations of ion-temperature-gradient (ITG) instability and turbulence in tokamak plasmas as well as some tokamak plasma thermal transport models, which have been widely used for predicting the performance of the proposed International Thermonuclear Experimental Reactor (ITER) tokamak [Plasma Physics and Controlled Nuclear Fusion Research, 1996 (International Atomic Energy Agency, Vienna, 1997), Vol. 1, p. 3], are compared. These comparisons provide information on effects of differences in the physics content of the various models and on the fusion-relevant figures of merit of plasma performance predicted by the models. Many of the comparisons are undertaken for a simplified plasma model and geometry which is an idealization of the plasma conditions and geometry in a Doublet III-D [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] high confinement (H-mode) experiment. Most of the models show good agreements in their predictions and assumptions for the linear growth rates and frequencies. There are some differences associated with different equilibria. However, there are significant differences in the transport levels between the models. The causes of some of the differences are examined in some detail, with particular attention to numerical convergence in the turbulence simulations (with respect to simulation mesh size, system size and, for particle-based simulations, the particle number). The implications for predictions of fusion plasma performance are also discussed.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.873896
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
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  • 10
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    Characterizing electron temperature gradient turbulence via numerical simulation
    AIP Publishing ; 2006
    In:  Physics of Plasmas Vol. 13, No. 12 ( 2006-12-01)
    Details
    In: Physics of Plasmas, AIP Publishing, Vol. 13, No. 12 ( 2006-12-01)
    Abstract: Numerical simulations of electron temperature gradient (ETG) turbulence are presented that characterize the ETG fluctuation spectrum, establish limits to the validity of the adiabatic ion model often employed in studying ETG turbulence, and support the tentative conclusion that plasma-operating regimes exist in which ETG turbulence produces sufficient electron heat transport to be experimentally relevant. We resolve prior controversies regarding simulation techniques and convergence by benchmarking simulations of ETG turbulence from four microturbulence codes, demonstrating agreement on the electron heat flux, correlation functions, fluctuation intensity, and rms flow shear at fixed simulation cross section and resolution in the plane perpendicular to the magnetic field. Excellent convergence of both continuum and particle-in-cell codes with time step and velocity-space resolution is demonstrated, while numerical issues relating to perpendicular (to the magnetic field) simulation dimensions and resolution are discussed. A parameter scan in the magnetic shear, s, demonstrates that the adiabatic ion model is valid at small values of s (s & lt;0.4 for the parameters used in this scan) but breaks down at higher magnetic shear. A proper treatment employing gyrokinetic ions reveals a steady increase in the electron heat transport with increasing magnetic shear, reaching electron heat transport rates consistent with analyses of experimental tokamak discharges.
    Type of Medium: Online Resource
    ISSN: 1070-664X , 1089-7674
    URL: Article
    DOI: 10.1063/1.2402510
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2006
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