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May 2005

Volume 12, Issue 5, Articles (05xxxx)

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back to top Magnetically Confined Plasmas, Heating, Confinement

Not completely flattened radial profile of the electron temperature in the vicinity of magnetic islands in Tokamak Chauffage Alfvén Brésilien

A. M. M. Fonseca, V. S. Tsypin, R. M. O. Galvão, Y. K. Kuznetsov, I. C. Nascimento, R. P. da Silva, E. A. Saettone, and A. Vannucci

Phys. Plasmas 12, 052501 (2005); http://dx.doi.org/10.1063/1.1889006 (7 pages) | Cited 3 times

Online Publication Date: 13 April 2005

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Recent results obtained in TCABR (Tokamak Chauffage Alfvén Brésilien) [ J. H. F. Severo, I. C. Nascimento, V. S. Tsypin, and R. M. O. Galvão, Nucl. Fusion 43, 1047 (2003) ] show a nonmonotonic variation of the poloidal rotation velocity at the position of major magnetic islands. In this paper, the associated effect of the magnetic islands on the radial profile of the electron temperature is discussed. Analytical temperature profiles are used to analyze the experimental data obtained with electron cyclotron emission radiometry. It is shown that the competition between strong anomalous perpendicular diffusive transport and parallel heat convection is the dominant mechanism for the oscillations observed in the radial profile of the electron temperature in TCABR.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.70.Gw Radio-frequency and microwave measurements
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)

Controlled and spontaneous magnetic field generation in a gun-driven spheromak

S. Woodruff, B. I. Cohen, E. B. Hooper, H. S. Mclean, B. W. Stallard, D. N. Hill, C. T. Holcomb, C. Romero-Talamas, R. D. Wood, G. Cone, and C. R. Sovinec

Phys. Plasmas 12, 052502 (2005); http://dx.doi.org/10.1063/1.1878772 (13 pages) | Cited 14 times

Online Publication Date: 13 April 2005

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In the Sustained Spheromak Physics Experiment, SSPX [ E. B. Hooper, D. Pearlstein, and D. D. Ryutov, Nucl. Fusion 39, 863 (1999) ], progress has been made in understanding the mechanisms that generate fields by helicity injection. SSPX injects helicity (linked magnetic flux) from 1 m diameter magnetized coaxial electrodes into a flux-conserving confinement region. Control of magnetic fluctuations (δB/B ∼ 1% on the midplane edge) yields Te profiles peaked at >200 eV. Trends indicate a limiting beta (βe ∼ 4%–6%), and so we have been motivated to increase Te by operating with stronger magnetic field. Two new operating modes are observed to increase the magnetic field: (A) Operation with constant current and spontaneous gun voltage fluctuations. In this case, the gun is operated continuously at the threshold for ejection of plasma from the gun: stored magnetic energy of the spheromak increases gradually with δB/B ∼ 2% and large voltage fluctuations (δV ∼ 1 kV), giving a 50% increase in current amplification, Itor/Igun. (B) Operation with controlled current pulses. In this case, spheromak magnetic energy increases in a stepwise fashion by pulsing the gun, giving the highest magnetic fields observed for SSPX ( ∼ 0.7 T along the geometric axis). By increasing the time between pulses, a quasisteady sustainment is produced (with periodic good confinement), comparing well with resistive magnetohydrodynamic simulations. In each case, the processes that transport the helicity into the spheromak are inductive and exhibit a scaling of field with current that exceeds those previously obtained. We use our newly found scaling to suggest how to achieve higher temperatures with a series of pulses.
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52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Predicting core and edge transport barriers in tokamaks using the GLF23 drift-wave transport model

J. E. Kinsey, G. M. Staebler, and R. E. Waltz

Phys. Plasmas 12, 052503 (2005); http://dx.doi.org/10.1063/1.1886826 (12 pages) | Cited 37 times

Online Publication Date: 13 April 2005

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The density and temperature profiles are predicted in core and edge transport barriers in the DIII-D tokamak [ J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985) ] using the GLF23 drift-wave model. The GLF23 model has been retuned to yield a better fit to the linear gyrokinetic growth rates for reversed magnetic shear and H-mode pedestal parameters. The turbulent saturation levels are determined using nonlinear gyrokinetic simulations. Using a large profile database, it is found that the retuned and original GLF23 models yield comparable results for discharges with monotonic safety factor profiles and no discernable internal transport barriers (ITBs). Examples of using retuned GLF23 model to predict the temperature profiles in simulations of several DIII-D strongly reversed magnetic shear ITB discharges are provided. Particle transport simulations show that the model is successful in predicting the density profile in discharges without ITBs but that some additional background particle diffusivity is needed in order to reproduce the measured density profiles within the barrier region of ITB plasmas where the ion temperature gradient and trapped electron mode transport have been quenched by rotational shear stabilization.
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52.25.Fi Transport properties
52.65.-y Plasma simulation
52.55.Fa Tokamaks, spherical tokamaks

Impact of a shearless flow and cylindricity on interchange instability in magnetized plasma

E. S. Benilov

Phys. Plasmas 12, 052504 (2005); http://dx.doi.org/10.1063/1.1886830 (9 pages)

Online Publication Date: 18 April 2005

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The stability of magnetically confined plasmas is sometimes examined using the so-called “slab” model, where the toroidal geometry of the problem is approximated locally by the Cartesian one. In the present paper, a (more accurate) cylindrical approximation is considered and shown to yield results which are qualitatively different from those of the slab model. In particular, if the slab model is applied to the outboard region of the tokamak (where the gradient of the plasma’s density and that of the magnetic field are of the same sign), disturbances remain unstable at all times. In the cylindrical model, on the other hand, the E×B flow carries disturbances around the cylinder and they alternate between the unstable and stable regions. Naturally, this reduces the growth rate of instability and makes it dependent on the angular velocity of the flow.
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52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.30.-q Plasma dynamics and flow
52.55.Fa Tokamaks, spherical tokamaks
52.25.Xz Magnetized plasmas

A simple highly accurate field-line mapping technique for three-dimensional Monte Carlo modeling of plasma edge transport

Y. Feng, F. Sardei, and J. Kisslinger

Phys. Plasmas 12, 052505 (2005); http://dx.doi.org/10.1063/1.1888959 (7 pages) | Cited 5 times

Online Publication Date: 20 April 2005

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The paper presents a new simple and accurate numerical field-line mapping technique providing a high-quality representation of field lines as required by a Monte Carlo modeling of plasma edge transport in the complex magnetic boundaries of three-dimensional (3D) toroidal fusion devices. Using a toroidal sequence of precomputed 3D finite flux-tube meshes, the method advances field lines through a simple bilinear, forward/backward symmetric interpolation at the interfaces between two adjacent flux tubes. It is a reversible field-line mapping (RFLM) algorithm ensuring a continuous and unique reconstruction of field lines at any point of the 3D boundary. The reversibility property has a strong impact on the efficiency of modeling the highly anisotropic plasma edge transport in general closed or open configurations of arbitrary ergodicity as it avoids artificial cross-field diffusion of the fast parallel transport. For stellarator-symmetric magnetic configurations, which are the standard case for stellarators, the reversibility additionally provides an average cancellation of the radial interpolation errors of field lines circulating around closed magnetic flux surfaces. The RFLM technique has been implemented in the 3D edge transport code EMC3-EIRENE and is used routinely for plasma transport modeling in the boundaries of several low-shear and high-shear stellarators as well as in the boundary of a tokamak with 3D magnetic edge perturbations.
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52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.65.Pp Monte Carlo methods
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
02.60.Ed Interpolation; curve fitting

Two-dimensional Harris–Liouville plasma kinetic equilibria

F. Ceccherini, C. Montagna, F. Pegoraro, and G. Cicogna

Phys. Plasmas 12, 052506 (2005); http://dx.doi.org/10.1063/1.1899083 (8 pages) | Cited 6 times

Online Publication Date: 22 April 2005

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Isothermal stationary solutions of the self-consistent Vlasov equation can be constructed for arbitrary two-dimensional sheared magnetic field configurations by exploiting a complex function representation of the solutions of the nonlinear Liouville equation. All these solutions are shown to be locally equivalent to the well known Harris sheet pinch configuration. Solutions corresponding to different magnetic configurations are presented, including a double Y-point configuration reminiscent of a reconnection current layer. Lie point symmetries are used to elucidate the relationship between the different configurations and to investigate the structure of the linearized perturbations in the “quasistatic” approximation.
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52.25.Dg Plasma kinetic equations
52.25.Fi Transport properties
52.65.Ff Fokker-Planck and Vlasov equation
52.25.Xz Magnetized plasmas

Additional evidence for the universality of the probability distribution of turbulent fluctuations and fluxes in the scrape-off layer region of fusion plasmas

B. Ph. van Milligen, R. Sánchez, B. A. Carreras, V. E. Lynch, B. LaBombard, M. A. Pedrosa, C. Hidalgo, B. Gonçalves, and R. Balbín

Phys. Plasmas 12, 052507 (2005); http://dx.doi.org/10.1063/1.1884615 (7 pages) | Cited 29 times

Online Publication Date: 22 April 2005

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Plasma density fluctuations and electrostatic turbulent fluxes measured at the scrape-off layer of the Alcator C-Mod tokamak [ B. LaBombard, R. L. Boivin, M. Greenwald, J. Hughes, B. Lipschultz, D. Mossessian, C. S. Pitcher, J. L. Terry, and S. J. Zweben, Phys. Plasmas 8, 2107 (2001) ], the Wendelstein 7-Advanced Stellarator [ H. Renner, E. Anabitarte, E. Ascasibar et al., Plasma Phys. Controlled Fusion 31, 1579 (1989) ], and the TJ-II stellarator [ C. Alejaldre, J. Alonso, J. Botija et al., Fusion Technol. 17, 131 (1990) ] are shown to obey a non-Gaussian but apparently universal (i.e., not dependent on device and discharge parameters) probability density distribution (pdf). The fact that a specific shape acts as an attractor for the pdf seems to suggest that emergent behavior and self-regulation are relevant concepts for these fluctuations. This shape is closely similar to the so-called Bramwell, Holdsworth, and Pinton distribution, which does not have any free parameters.
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52.25.Gj Fluctuation and chaos phenomena
52.25.Fi Transport properties
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Fa Tokamaks, spherical tokamaks
52.55.Jd Magnetic mirrors, gas dynamic traps
52.35.Ra Plasma turbulence

Density dependence of trace tritium transport in H-mode Joint European Torus plasma

I. Voitsekhovitch, X. Garbet, D. C. McDonald, K.-D. Zastrow, M. Adams, Yu. Baranov, P. Belo, L. Bertalot, R. Budny, S. Conroy, J. G. Cordey, L. Garzotti, P. Mantica, D. McCune, J. Ongena, et al.

Phys. Plasmas 12, 052508 (2005); http://dx.doi.org/10.1063/1.1895887 (12 pages) | Cited 7 times

Online Publication Date: 28 April 2005

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Tritium transport in edge localized mode (ELM) high confinement (H-mode) plasmas is analyzed here as a function of density for discharges from the recent trace tritium experimental campaign performed on Joint European Torus. In this campaign small amounts of tritium have been puffed or injected (with neutral beam injectors) into deuterium plasmas [ K.-D. Zastrow, J. M. Adams, Yu. Baranov et al., Plasma Phys. Controlled Fusion 46, B255 (2004) ]. Information about the tritium has been obtained from the evolution of the profiles of neutron emission simulated via the TRANSP [ R. J. Goldston, D. C. McCune, H. H. Towner, S. L. Davis, R. J. Hawryluk, and G. L. Schmidt, J. Comput. Phys. 43, 61 (1981) ] and SANCO (L. Lauro-Taroni, B. Alper, R. Giannella, K. Lawson, F. Marcus, M. Mattioli, P. Smeulders, and M. Von Hellermann, Proceedings of the 21st European Conference on Controlled Fusion and Plasma Physics, Montpelier, France, 1994) codes. A strong inverse correlation of tritium transport with plasma density is found in this analysis. The low tritium transport at high density is close to neoclassical values while the transport becomes strongly anomalous in low density plasmas. The thermal transport does not exhibit such a strong density dependence, leading to a varying ratio of thermal to tritium transport in these discharges. An interpretation of the density effects on the trace tritium transport, partially based on the test particle simulations in plasmas with stochastic magnetic field, is proposed. A simple model for the tritium diffusion coefficient and convective velocity, which includes the modification of the neoclassical particle diffusion in presence of electromagnetic turbulence [ A. I. Smolyakov and P. N. Yushmanov, Nucl. Fusion 35, 383 (1993) ] completed with an empirical density dependence, is developed. This model has positive β dependence in agreement with the results of the similarity experiments performed for trace tritium transport.
Show PACS
52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.80.-s Electric discharges
52.50.Gj Plasma heating by particle beams
52.40.Hf Plasma-material interactions; boundary layer effects
52.35.Qz Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.65.-y Plasma simulation
52.35.Ra Plasma turbulence
52.25.Tx Emission, absorption, and scattering of particles
52.25.Ya Neutrals in plasmas

Electron Bernstein wave-bootstrap current synergy in the National Spherical Torus Experiment

R. W. Harvey and G. Taylor

Phys. Plasmas 12, 052509 (2005); http://dx.doi.org/10.1063/1.1893586 (8 pages)

Online Publication Date: 2 May 2005

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Current driven by electron Bernstein waves (EBW) and by the electron bootstrap effect are calculated separately and concurrently with a kinetic code to determine the degree of synergy between them. A target β = 40% NSTX [ M. Ono, S. Kaye, M. Peng et al., Proceedings of the 17th IAEA Fusion Energy Conference, edited by M. Spak (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135 ] plasma is examined. A simple bootstrap model in the collisional-quasilinear CQL3D Fokker–Planck code (National Technical Information Service document No. DE93002962) is used in these studies: the transiting electron distributions are connected in velocity space at the trapped-passing boundary to trapped-electron distributions that are displaced radially by a half-banana-width outwards/inwards for the co-passing/counter-passing regions. This model agrees well with standard bootstrap current calculations over the outer 60% of the plasma radius. Relatively small synergy net bootstrap current is obtained for EBW power up to 4 MW. Locally, bootstrap current density increases in proportion to increased plasma pressure, and this effect can significantly affect the radial profile of driven current.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.55.-s Magnetic confinement and equilibrium
52.20.Fs Electron collisions
52.25.Dg Plasma kinetic equations
52.65.Ff Fokker-Planck and Vlasov equation
52.25.Fi Transport properties

Role of thermal instabilities and anomalous transport in threshold of detachment and multifacetted asymmetric radiation from the edge (MARFE)

M. Z. Tokar, F. A. Kelly, and X. Loozen

Phys. Plasmas 12, 052510 (2005); http://dx.doi.org/10.1063/1.1897389 (12 pages) | Cited 10 times

Online Publication Date: 2 May 2005

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A model for the plasma edge in limiter tokamaks is elaborated, which permits us to investigate the synergy of impurity radiation, particle recycling, and edge turbulence phenomena in the formation of large-scale structures, in particular, of multifacetted asymmetric radiation from the edge. The model includes a description for the anomalous transport of charged particles induced by drift microinstabilities most typical under edge conditions. Computations show that the pattern of structures, developing when a critical plasma density is approached, is essentially determined by the poloidal inhomogeneities introduced from the Shafranov shift of magnetic surfaces and from the ballooning character of edge turbulence.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.55.Fa Tokamaks, spherical tokamaks

Efficient coupling of thermal electron Bernstein waves to the ordinary electromagnetic mode on the National Spherical Torus Experiment

G. Taylor, P. C. Efthimion, B. P. LeBlanc, M. D. Carter, J. B. Caughman, J. B. Wilgen, J. Preinhaelter, R. W. Harvey, and S. A. Sabbagh

Phys. Plasmas 12, 052511 (2005); http://dx.doi.org/10.1063/1.1891065 (7 pages) | Cited 11 times

Online Publication Date: 5 May 2005

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Efficient coupling of thermal electron Bernstein waves (EBW) to ordinary-mode (O-mode) electromagnetic radiation has been measured in plasmas heated by energetic neutral beams and high harmonic fast waves in the National Spherical Torus Experiment (NSTX) [ M. Ono, S. Kaye, M. Peng et al., Proceedings of the 17th IAEA Fusion Energy Conference, edited by S. Spak (IAEA, Vienna, Austria, 1999), Vol. 3, p. 1135 ]. The EBW to electromagnetic mode coupling efficiency was measured to be 0.8±0.2, compared to a numerical EBW modeling prediction of 0.65. The observation of efficient EBW coupling to O mode, in relatively good agreement with numerical modeling, is a necessary prerequisite for implementing a proposed high power EBW current drive system on NSTX.
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52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.50.Gj Plasma heating by particle beams
52.25.Fi Transport properties
52.55.-s Magnetic confinement and equilibrium

Characterization of core and edge turbulence in L- and enhanced Dα H-mode Alcator C-Mod plasmas

N. P. Basse, E. M. Edlund, D. R. Ernst, C. L. Fiore, M. J. Greenwald, A. E. Hubbard, J. W. Hughes, J. H. Irby, L. Lin, Y. Lin, E. S. Marmar, D. A. Mossessian, M. Porkolab, J. E. Rice, J. A. Snipes, et al.

Phys. Plasmas 12, 052512 (2005); http://dx.doi.org/10.1063/1.1899161 (14 pages) | Cited 5 times

Online Publication Date: 5 May 2005

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The recently upgraded phase-contrast imaging (PCI) diagnostic is used to characterize the transition from the low (L) to the enhanced Dα (EDA) high (H) confinement mode in Alcator C-Mod [ I. H. Hutchinson, R. Boivin, F. Bombarda et al., Phys. Plasmas 1, 1511 (1994) ] plasmas. PCI yields information on line integrated density fluctuations along vertical chords. The number of channels has been increased from 12 to 32 and the sampling rate from 1 MHz to 10 MHz. This expansion of diagnostic capabilities is used to study broadband turbulence in L and EDA H mode and to analyze the quasicoherent (QC) mode associated with EDA H mode. Changes in broadband turbulence at the transition from L to EDA H mode can be interpreted as an effect of the Doppler rotation of the bulk plasma. Additional fluctuation measurements of Dα light and the poloidal magnetic field show features correlated with PCI in two different frequency ranges at the transition. The backtransition from EDA H to L mode, the so-called enhanced neutron (EN) mode, is investigated by new high frequency (132 and 140 GHz) reflectometer channels operating in the ordinary (O) mode. This additional hardware has been installed in an effort to study localized turbulence associated with internal transport barriers (ITBs). The EN mode is a suitable candidate for this study, since an ITB exists transiently as the outer density decreases much faster than the core density in this mode. The fact that the density decays from the outside inward allows us to study fluctuations progressing towards the plasma core. Our results mark the first localized observation of the QC mode at medium density: 2.2×1020 m−3 (132 GHz). Correlating the reflectometry measurements with other fluctuating quantities provides some insight regarding the causality of the EN-mode development.
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52.25.Gj Fluctuation and chaos phenomena
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Ra Plasma turbulence

Confinement analyses of the high-density field-reversed configuration plasma in the field-reversed configuration experiment with a liner

Shouyin Zhang, T. P. Intrator, G. A. Wurden, W. J. Waganaar, J. M. Taccetti, R. Renneke, C. Grabowski, and E. L. Ruden

Phys. Plasmas 12, 052513 (2005); http://dx.doi.org/10.1063/1.1899648 (8 pages) | Cited 9 times

Online Publication Date: 5 May 2005

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The focus of the field-reversed configuration (FRC) experiment with a liner (FRX-L) is the formation of a target FRC plasma for magnetized target fusion experiments. An FRC plasma with density of 1023 m−3, total temperature in the range of 150–300 eV, and a lifetime of ≈ 20 μs is desired. Field-reversed θ-pinch technology is used with programed cusp fields at θ-coil ends to achieve non-tearing field line reconnections during FRC formation. Well-formed FRCs with density between (2–4)×1022 m−3, lifetime in the range of 15–20 μs, and total temperature between 300–500 eV are reproducibly created. Key FRC parameters have standard deviation in the mean of 10% during consecutive shots. The FRCs are formed at 50 mTorr deuterium static fill using 2 kG net reversed bias field inside the θ-coil confinement region, with external main field unexpectedly ranging between 15–30 kG. The high-density FRCs confinement properties are approximately in agreement with empirical scaling laws obtained from previous experiments with fill pressure mostly less than 20 mTorr. Analyses in this paper reveal that reducing the external main field modulation and∕or extending the θ-coil length in the FRX-L device are critical in achieving higher FRC parameters for application in magnetized target fusion.
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52.55.Ez Theta pinch
52.25.Xz Magnetized plasmas
52.50.Lp Plasma production and heating by shock waves and compression

Time-dependent plasma viscosity and poloidal flow damping with orbit squeezing in tokamaks

K. C. Shaing

Phys. Plasmas 12, 052514 (2005); http://dx.doi.org/10.1063/1.1899663 (5 pages) | Cited 6 times

Online Publication Date: 5 May 2005

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In the vicinity of a magnetic island and in the zonal flow, the radial extent of the radial electric field layer is about the width of the ion poloidal gyroradius in tokamaks. Thus, the effects of the orbit squeezing become important in these situations and probably in other applications as well. It is shown that the poloidal flow damping rate in tokamaks is reduced approximately by a factor of ∣S∣ when the effects of orbit squeezing are taken into account. Here, S is the orbit-squeezing factor. Thus, the plasma confinement could be improved when the effects of the orbit squeezing are included in the turbulence simulations.
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52.25.Fi Transport properties
52.55.Fa Tokamaks, spherical tokamaks
52.25.Dg Plasma kinetic equations

Shear flow generation and energetics in electromagnetic turbulence

V. Naulin, A. Kendl, O. E. Garcia, A. H. Nielsen, and J. Juul Rasmussen

Phys. Plasmas 12, 052515 (2005); http://dx.doi.org/10.1063/1.1905603 (10 pages) | Cited 45 times

Online Publication Date: 5 May 2005

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Zonal flows are recognized to play a crucial role for magnetized plasma confinement. The genesis of these flows out of turbulent fluctuations is therefore of significant interest. Here the relative importance of zonal flow generation mechanisms via the Reynolds stress, Maxwell stress, and geodesic acoustic mode (GAM) transfer in drift-Alfvén turbulence is investigated. By means of numerical computations the energy transfer into zonal flows owing to each of these effects is quantified. The importance of the three driving ingredients in electrostatic and electromagnetic turbulence for conditions relevant to the edge of fusion devices is revealed for a broad range of parameters. The Reynolds stress is found to provide a flow drive, while the electromagnetic Maxwell stress is in the cases considered a sink for the flow energy. In the limit of high plasma β, where electromagnetic effects and Alfvén dynamics are important, the Maxwell stress is found to cancel the Reynolds stress to a high degree. The geodesic oscillations, related to equilibrium pressure profile modifications due to poloidally asymmetric transport, can act as both sinks as drive terms, depending on the parameter regime. For high-β cases the GAMs are the main drive of the flow. This is also reflected in the frequency dependence of the zonal flows, showing a distinct peak at the GAM frequency in that regime.
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52.25.Gj Fluctuation and chaos phenomena
52.35.Ra Plasma turbulence
52.65.Kj Magnetohydrodynamic and fluid equation

Time-dependent neoclassical viscosity

A. L. Garcia-Perciante, J. D. Callen, K. C. Shaing, and C. C. Hegna

Phys. Plasmas 12, 052516 (2005); http://dx.doi.org/10.1063/1.1899159 (11 pages) | Cited 3 times

Online Publication Date: 9 May 2005

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A time-dependent closure for the parallel viscous force is calculated in a bumpy cylinder magnetic field geometry using a Chapman–Enskog-like approach. The calculation is valid for all times and field modulations, and is expressed as a dynamic evolution in time. Two important applications are presented: modification of the frequency-dependent electrical conductivity due to the interaction between trapped and circulating particles, and the parallel flow evolution which can be extended to axisymmetric geometries.
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52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.30.-q Plasma dynamics and flow
52.25.Dg Plasma kinetic equations
52.55.-s Magnetic confinement and equilibrium

Nonlocal nonlinear electrostatic gyrofluid equations: A four-moment model

D. Strintzi, B. D. Scott, and A. J. Brizard

Phys. Plasmas 12, 052517 (2005); http://dx.doi.org/10.1063/1.1895886 (10 pages) | Cited 19 times

Online Publication Date: 11 May 2005

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Extending a previous single-temperature model, an electrostatic gyrofluid model that includes anisotropic temperatures (T‖ ≠ T⊥) and can treat general nonlinear situations is constructed. The model is based on a Lagrangian formulation of gyrofluid dynamics, which leads to an exact energy conservation law. Diamagnetic cancellations are inserted manually in such a way that energy conservation is preserved. Comparison with previous models shows a very good agreement for zero-Larmor-radius terms in the gyrofluid equations of motion.
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52.35.Ra Plasma turbulence
52.30.Ex Two-fluid and multi-fluid plasmas
52.65.Tt Gyrofluid and gyrokinetic simulations

Edge-localized modes and edge transport in spherical tokamaks

Robert G. Kleva and Parvez N. Guzdar

Phys. Plasmas 12, 052518 (2005); http://dx.doi.org/10.1063/1.1914806 (5 pages) | Cited 4 times

Online Publication Date: 11 May 2005

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Turbulent energy transport in numerical simulations of the edge region of spherical tokamaks with small toroidal aspect ratio A = 1.5 is directly compared to that in conventional tokamaks with larger aspect ratio A = 3. Depending upon the aspect ratio of the torus, the energy flux can vary greatly. While a tokamak plasma with aspect ratio A = 3 is in the high (H) mode where the transport rate is small, an otherwise identical tokamak plasma with small aspect ratio A = 1.5 exhibits extremely poor confinement. The magnitude of the energy flux in these two cases differs by a multiplicative factor larger than 50. However, good H mode confinement in small aspect ratio spherical tokamaks can be obtained by a further increase in the edge density gradient. Confinement is then dominated by bursts of ballooning modes which periodically transport energy to large major radius. The periodic bursts in the numerical simulations are similar to the periodic radiation bursts that characterize edge-localized modes in tokamaks.
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52.55.Fa Tokamaks, spherical tokamaks
52.35.Ra Plasma turbulence
52.25.Fi Transport properties
52.65.Kj Magnetohydrodynamic and fluid equation
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Implicit solution of the four-field extended-magnetohydrodynamic equations using high-order high-continuity finite elements

S. C. Jardin and J. A. Breslau

Phys. Plasmas 12, 056101 (2005); http://dx.doi.org/10.1063/1.1864992 (10 pages) | Cited 13 times

Online Publication Date: 7 April 2005

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Here we describe a technique for solving the four-field extended-magnetohydrodynamic (MHD) equations in two dimensions. The introduction of triangular high-order finite elements with continuous first derivatives (C1 continuity) leads to a compact representation compatible with direct inversion of the associated sparse matrices. The split semi-implicit method is introduced and used to integrate the equations in time, yielding unconditional stability for arbitrary time step. The method is applied to the cylindrical tilt mode problem with the result that a nonzero value of the collisionless ion skin depth will increase the growth rate of that mode. The effect of this parameter on the reconnection rate and geometry of a Harris equilibrium and on the Taylor reconnection problem is also demonstrated. This method forms the basis for a generalization to a full extended-MHD description of the plasma with six, eight, or more scalar fields.
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52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)

Active and fast particle driven Alfvén eigenmodes in Alcator C-Mod

J. A. Snipes, N. Basse, C. Boswell, E. Edlund, A. Fasoli, N. N. Gorelenkov, R. S. Granetz, L. Lin, Y. Lin, R. Parker, M. Porkolab, J. Sears, S. Sharapov, V. Tang, and S. Wukitch

Phys. Plasmas 12, 056102 (2005); http://dx.doi.org/10.1063/1.1865012 (8 pages) | Cited 45 times

Online Publication Date: 7 April 2005

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Alfvén eigenmodes (AEs) are studied to assess their stability in high density reactor relevant regimes where Ti ≈ Te and as a diagnostic tool. Stable AEs are excited with active magnetohydrodynamics antennas in the range of the expected AE frequency. Toroidal Alfvén eigenmode (TAE) damping rates between 0.5%<γ/ω<4.5% have been observed in diverted and limited Ohmic plasmas. Unstable AEs are excited with a fast ion tail driven by H minority ion cyclotron radio frequency (ICRF) heating with electron densities in the range of mathe = 0.5–2×1020 m−3. Energetic particle modes or TAEs have been observed to decrease in frequency and mode number with time up to a large sawtooth collapse, indicating the role fast particles play in stabilizing sawteeth. In the current rise phase, unstable modes with frequencies that increase rapidly with time are observed with magnetic pick-up coils at the wall and phase contrast imaging density fluctuation measurements in the core. Modeling of these modes constrains the calculated safety factor profile to be very flat or with slightly reversed shear. AEs are found to be more stable for an inboard than for central or outboard ICRF resonances in qualitative agreement with modeling.
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52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.55.Fa Tokamaks, spherical tokamaks
52.25.Fi Transport properties
52.25.Gj Fluctuation and chaos phenomena
52.30.Cv Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Bj Magnetohydrodynamic waves (e.g., Alfven waves)
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.40.Hf Plasma-material interactions; boundary layer effects
52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.50.Nr Plasma heating by DC fields; ohmic heating, arcs
52.70.Ds Electric and magnetic measurements
52.70.Gw Radio-frequency and microwave measurements

Pellet fueling technology development leading to efficient fueling of ITER burning plasmas

L. R. Baylor, S. K. Combs, T. C. Jernigan, W. A. Houlberg, L. W. Owen, D. A. Rasmussen, S. Maruyama, and P. B. Parks

Phys. Plasmas 12, 056103 (2005); http://dx.doi.org/10.1063/1.1865052 (6 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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Pellet injection is the primary fueling technique planned for core fueling of ITER [ITER Technical Basis 2002 ITER EDA Documentation Series (Vienna: IAEA)] burning plasmas. Efficient core plasma fueling with deuterium and tritium D–T is a requirement for achieving high fusion gain and it cannot be achieved with gas fueling. Injection of pellets from the inner wall has been shown on present day tokamarks to provide efficient fueling and is planned for use on ITER. Modeling of the fueling deposition from inner wall pellet injection using the Parks E×B drift model indicates that pellets have the capability to fuel well inside the separatrix. Gas fueling calculations show very poor neutral penetration due to the high density and wide scrape off layer. Isotopically mixed D–T pellets can provide efficient tritium fueling that will minimize tritium wall loading when compared to gas puffing. Currently the performance of the ITER inner wall guide tube design is under test with initial results indicating that pellet speeds in excess of 300 m/s will lead to fragmented pellets. The ITER pellet injection technology requirements and remaining development issues are discussed along with a plan to reach the design goal for employment on ITER.
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52.50.Gj Plasma heating by particle beams
52.25.Ya Neutrals in plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
52.55.Pi Fusion products effects (e.g., alpha-particles, etc.), fast particle effects
52.55.Fa Tokamaks, spherical tokamaks
28.52.Cx Fueling, heating and ignition
28.52.Fa Materials

Ion cyclotron range of frequency mode conversion physics in Alcator C-Mod: Experimental measurements and modeling

S. J. Wukitch, Y. Lin, A. Parisot, J. C. Wright, P. T. Bonoli, M. Porkolab, N. Basse, E. Edlund, A. Hubbard, L. Lin, A. Lynn, E. Marmar, D. Mossessian, P. Phillips, and G. Schilling

Phys. Plasmas 12, 056104 (2005); http://dx.doi.org/10.1063/1.1866142 (8 pages) | Cited 11 times

Online Publication Date: 7 April 2005

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In ion cyclotron range of frequency experiments, we have simultaneously measured the incident fast wave and the mode converted waves in the mode conversion region in D(math) plasmas using an upgraded phase contrast imaging diagnostic in the Alcator C-Mod tokamak [ I. H. Hutchinson, R. Boivin, F. Bombarida et al., Phys. Plasmas 1, 1511 (1994) ]. To experimentally validate the full wave TORIC [ M. Brambilla, Nucl. Fusion 38, 1805 (1998) ] physics kernel, the simulated power deposition and line integrated perturbed density profiles were compared with experimental profiles and are found to be in remarkably good agreement with the experimentally determined profiles. This suggests the physics model and computation algorithm used in TORIC, particularly for the mode converted waves, model the mode conversion physics well. We also report results from initial mode conversion current drive experiments where the modification of the sawtooth period was clearly observed and was shown to depend on antenna phasing suggesting the presence of a localized driven current.
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52.50.Qt Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.25.Fi Transport properties
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
52.70.Gw Radio-frequency and microwave measurements

Probabilistic transport models for plasma transport in the presence of critical thresholds: Beyond the diffusive paradigm

R. Sánchez, B. Ph. van Milligen, and B. A. Carreras

Phys. Plasmas 12, 056105 (2005); http://dx.doi.org/10.1063/1.1869499 (7 pages) | Cited 18 times

Online Publication Date: 7 April 2005

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It is argued that the modeling of plasma transport in tokamaks may benefit greatly from extending the usual local paradigm to accommodate scale-free transport mechanisms. This can be done by combining Lévy distributions and a nonlinear threshold condition within the continuous time random walk concept. The advantages of this nonlocal, nonlinear extension are illustrated by constructing a simple particle density transport model that, as a result of these ideas, spontaneously exhibits much of nondiffusive phenomenology routinely observed in tokamaks. The fluid limit of the system shows that the kind of equations that are appropriate to capture these dynamics are based on fractional differential operators. In them, effective diffusivities and pinch velocities are found that are dynamically set by the system in response to the specific characteristics of the fueling source and external perturbations. This fact suggests some dramatic consequences for the extrapolation of these transport properties to larger size systems.
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52.25.Fi Transport properties
52.30.-q Plasma dynamics and flow
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.55.Fa Tokamaks, spherical tokamaks
05.40.Fb Random walks and Levy flights
02.50.Cw Probability theory

Simulation of spheromak evolution and energy confinement

B. I. Cohen, E. B. Hooper, R. H. Cohen, D. N. Hill, H. S. McLean, R. D. Wood, S. Woodruff, C. R. Sovinec, and G. A. Cone

Phys. Plasmas 12, 056106 (2005); http://dx.doi.org/10.1063/1.1869501 (9 pages) | Cited 22 times

Online Publication Date: 7 April 2005

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Simulation results are presented that illustrate the formation and decay of a spheromak plasma driven by a coaxial electrostatic plasma gun, and model the plasma energy confinement. The physics of magnetic reconnection during formation is also illuminated. The simulations are performed with the three-dimensional, time-dependent, resistive magnetohydrodynamic NIMROD code [ C. R. Sovinec, A. H. Glasser, T. A. Gianakon, D. C. Barnes, R. A. Nebel, S. E. Kruger, D. D. Schnack, S. J. Plimpton, A. Tarditi, and M. S. Chu, J. Comput. Phys. 195, 355 (2004) ]. The simulation results are compared to data from the Sustained Spheromak Physics Experiment (SSPX) [ E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999) ]. The simulation results are tracking SSPX with increasing fidelity (e.g., improved agreement with measured magnetic fields, fluctuation amplitudes, and electron temperature) as the simulation has been improved in its representations of the experimental geometry, the magnetic bias coils, and the detailed time dependence of the current source driving the plasma gun, and uses realistic parameters. The simulations confirm that controlling the magnetic fluctuations is influenced by the current drive history and by matching the gun current in sustainment approximately to the value corresponding to the eigenvalue in the flux-conserver for the parallel current in a force-free equilibrium.
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52.65.-y Plasma simulation

Magnetohydrodynamics equilibria with toroidal and poloidal flow

L. Guazzotto and R. Betti

Phys. Plasmas 12, 056107 (2005); http://dx.doi.org/10.1063/1.1869502 (10 pages) | Cited 19 times

Online Publication Date: 7 April 2005

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In the present work, the effects of flow on tokamak equilibria are investigated, focusing in particular on the effects of poloidal flows. It is shown that discountinuous transonic equilibria with a pedestal structure can be obtained for relatively low values of the poloidal velocity. Equilibria with poloidal flow of the order of the poloidal Alfvén speed are shown to develop inverted Shafranov shift. Since the rotation is damped by the neoclassical poloidal viscosity, a quasi-omnigenous solution for equilibria with large rotation is also derived in order to minimize the flow damping. In this solution, the magnetic field is construed to be a function of the poloidal magnetic flux Ψ up to a small correction by an appropriate choice of the flow profiles. All numerical results are obtained with the code FLOW [L. Guazzotto, R. Betti, J. Manickam, and S. Kaye, Phys. Plasmas 11, 604 (2004) ].
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52.55.Fa Tokamaks, spherical tokamaks
52.65.-y Plasma simulation
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