Phys. Plasmas (1994-Present) - Physics of Plasmas

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Announcement: The 2009 James Clerk Maxwell Prize for Plasma Physics

Ronald C. Davidson

Phys. Plasmas 17, 010201 (2010); http://dx.doi.org/10.1063/1.3273205 (2 pages)

Online Publication Date: 4 January 2010

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99.10.Np

Editorial note

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Observation and characterization of laser-driven phase space electron holes

G. Sarri, M. E. Dieckmann, C. R. D. Brown, C. A. Cecchetti, D. J. Hoarty, S. F. James, R. Jung, I. Kourakis, H. Schamel, O. Willi, and M. Borghesi

Phys. Plasmas 17, 010701 (2010); http://dx.doi.org/10.1063/1.3286438 (4 pages) | Cited 9 times

Online Publication Date: 7 January 2010

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The direct observation and full characterization of a phase space electron hole (EH) generated during laser-matter interaction is presented. This structure, propagating in a tenuous, nonmagnetized plasma, has been detected via proton radiography during the irradiation with a ns laser pulse (Iλ² ≈ 10¹⁴ W/cm²) of a gold hohlraum. This technique has allowed the simultaneous detection of propagation velocity, potential, and electron density spatial profile across the EH with fine spatial and temporal resolution allowing a detailed comparison with theoretical and numerical models.

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52.38.Ph	X-ray, γ-ray, and particle generation
52.70.Nc	Particle measurements
52.25.Tx	Emission, absorption, and scattering of particles

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A statistical model of magnetic islands in a current layer

R. L. Fermo, J. F. Drake, and M. Swisdak

Phys. Plasmas 17, 010702 (2010); http://dx.doi.org/10.1063/1.3286437 (4 pages) | Cited 4 times

Online Publication Date: 25 January 2010

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This letter describes a statistical model of the dynamics of magnetic islands in very large current layers that develop in space plasma. Two parameters characterize the island distribution: the flux ψ contained in the island and the area A it encloses. The integrodifferential evolution equation for this distribution function is based on rules that govern the small-scale generation of secondary islands, the rates of island growth, and island merging. The numerical solutions of this equation produce island distributions relevant to the magnetosphere and solar corona. The solution of a differential equation for large islands explicitly shows the role merging plays in island growth.

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52.35.Vd	Magnetic reconnection
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Rr	Particle-in-cell method
96.60.P-	Corona
95.30.Qd	Magnetohydrodynamics and plasmas
94.05.-a	Space plasma physics

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Suppression of Landau damping via electron band gap

S. Son and S. Ku

Phys. Plasmas 17, 010703 (2010); http://dx.doi.org/10.1063/1.3298735 (4 pages) | Cited 7 times

Online Publication Date: 26 January 2010

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The pondermotive potential in the x-ray Raman compression can generate an electron band gap, which suppresses the Landau damping. The regime is identified where a Langmuir wave can be driven without damping in the stimulated Raman compression. It is shown that the partial wave breaking and the frequency detuning due to the trapped particles would be greatly reduced.

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52.38.Ph	X-ray, γ-ray, and particle generation
52.38.Kd	Laser-plasma acceleration of electrons and ions
52.25.Mq	Dielectric properties

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Modeling of impurity effect on drift instabilities in plasmas with many ion species

S. Moradi, M. Z. Tokar, and B. Weyssow

Phys. Plasmas 17, 012101 (2010); http://dx.doi.org/10.1063/1.3283390 (10 pages) | Cited 4 times

Online Publication Date: 6 January 2010

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Drift microinstabilities, being the main cause of anomalous transport of charged particles and energy in fusion plasmas, can be strongly influenced by the presence of impurities. Normally a large amount of different ion species from diverse charge states and chemical elements is present. An approach, providing a possibility to take into account an arbitrary number of ion species in analysis of instabilities, is proposed and applied to study the impurity effect on unstable modes due to ion temperature gradient and trapped electrons described in a linear fluid approximation. The method is validated by comparing with the results from direct calculations in a one impurity ion case. The dependence of instability characteristics and anomalous transport coefficients on the absolute level and radial gradient of impurity density is investigated. Plasmas with several impurity ion species, including C⁺⁶, N⁺⁷, O⁺⁸, Ne⁺¹⁰, and Ar⁺¹⁸ whose density peaking factors are determined self-consistently from the impurity zero flux condition, are considered as an example of applications.

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52.25.Vy

Impurities in plasmas

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Generation of whistler waves by a rotating magnetic field source

A. V. Karavaev, N. A. Gumerov, K. Papadopoulos, Xi Shao, A. S. Sharma, W. Gekelman, A. Gigliotti, P. Pribyl, and S. Vincena

Phys. Plasmas 17, 012102 (2010); http://dx.doi.org/10.1063/1.3274916 (13 pages) | Cited 4 times

Online Publication Date: 6 January 2010

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The paper discusses the generation of polarized whistler waves radiated from a rotating magnetic field source created via a novel phased orthogonal two loop antenna. The results of linear three-dimensional electron magnetohydrodynamics simulations along with experiments on the generation whistler waves by the rotating magnetic field source performed in the large plasma device are presented. Comparison of the experimental results with the simulations and linear wave properties shows good agreement. The whistler wave dispersion relation with nonzero transverse wave number and the wave structure generated by the rotating magnetic field source are also discussed. The phase velocity of the whistler waves was found to be in good agreement with the theoretical dispersion relation. The exponential decay rate of the whistler wave propagating along the ambient magnetic field is determined by Coulomb collisions. In collisionless case the rotating magnetic field source was found to be a very efficient radiation source for transferring energy along the ambient magnetic field lines.

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52.35.Hr	Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)
52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
52.40.Fd	Plasma interactions with antennas; plasma-filled waveguides
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.20.-j	Elementary processes in plasmas
52.65.Kj	Magnetohydrodynamic and fluid equation

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Modulational instability of ion-acoustic wave envelopes in magnetized quantum electron-positron-ion plasmas

A. S. Bains, A. P. Misra, N. S. Saini, and T. S. Gill

Phys. Plasmas 17, 012103 (2010); http://dx.doi.org/10.1063/1.3293119 (7 pages) | Cited 5 times

Online Publication Date: 15 January 2010

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The amplitude modulation of quantum ion-acoustic waves (QIAWs) along an external magnetic field is studied in a quantum electron-positron-ion (e-p-i) magnetoplasma. Reductive perturbation technique is used to derive the three-dimensional nonlinear Schrödinger equation which governs the slow modulation of QIAW packets. Accounting for the effects of the electron to ion number density ratio (μ), the normalized ion-cyclotron frequency (ω_c) as well as the ratio (H) of the “plasmonic energy density” to the Fermi energy, new regimes for the modulational instability of QIAWs are obtained and analyzed. In contrast to one-dimensional unmagnetized e-p-i plasmas, the instability growth rate is shown to suppress with increasing μ or decreasing the values of H. The predicted results could be important for understanding the salient features of modulated QIAW packets in dense astrophysical plasmas as well as to the next generation intense laser solid density plasma experiments.

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52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Sb	Solitons; BGK modes
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.27.Ep	Electron-positron plasmas

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The reflection of an electromagnetic wave from the self-produced plasma

M. Mirzaie, B. Shokri, and A. A. Rukhadze

Phys. Plasmas 17, 012104 (2010); http://dx.doi.org/10.1063/1.3292654 (6 pages) | Cited 1 time

Online Publication Date: 15 January 2010

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The dynamic behavior of a high power microwave beam propagating through a gaseous medium, which is ionized in the wave field is investigated. By solving the wave equation, the reflection index of the produced plasma is obtained. It is shown that the cut off condition is different from that of the steady state approximation. The reflection index is less than unity when the plasma density reaches the critical value estimated in the steady state approximation. So, the wave can still propagate through the plasma. By comparing the reflection indexes in the presence and absence of the time delay of the ionization process at different points of the medium, it is shown that it becomes unity much later in the first case. Therefore, the wave propagation takes much more time and consequently the medium is ionized much more.

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52.40.Db	Electromagnetic (nonlaser) radiation interactions with plasma
52.25.-b	Plasma properties

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Electromagnetic drift instabilities in high-β plasma under conditions of a field reversed configuration

A. Yu. Chirkov and V. I. Khvesyuk

Phys. Plasmas 17, 012105 (2010); http://dx.doi.org/10.1063/1.3283399 (8 pages) | Cited 2 times

Online Publication Date: 15 January 2010

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Electromagnetic drift instabilities are studied in the conditions of a field reversed configuration (FRC). Dispersion equation is based on the set of Vlasov–Maxwell equations taking into account nonadiabatic responses both of ions and electrons. Considered drift instabilities are caused by density and temperature gradients. It is assumed that magnetic field of the FRC is purely poloidal. Two kinds of magnetic field nonuniformity are considered: (i) perpendicular gradient due to high β values (β is the plasma pressure/magnetic pressure) and (ii) curvature of magnetic lines. There is low frequency drift instability existing for high-β regimes. Modes of such instability can propagate transversally to the unperturbed magnetic field lines.

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52.35.Kt	Drift waves
52.55.Lf	Field-reversed configurations, rotamaks, astrons, ion rings, magnetized target fusion, and cusps

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Ion acoustic solitary waves and double layers in dense electron-positron-ion magnetoplasma

Prasanta Chatterjee, Taraknath Saha, S. V. Muniandy, C. S. Wong, and Rajkumar Roychoudhury

Phys. Plasmas 17, 012106 (2010); http://dx.doi.org/10.1063/1.3291059 (8 pages) | Cited 3 times

Online Publication Date: 15 January 2010

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The existence of ion acoustic solitary waves is studied in a magnetized dense electron-positron-ion plasma. The ions are described by the hydrodynamic equations, and the electron and positron are assumed to follow the Thomas–Fermi density distribution. The pseudopotential is derived directly from the basic equations including Poisson’s equation without assuming the quasineutrality condition. The effect of ion temperature on the solitary waves is studied, and the ranges of parameters for which solitary waves and double layers exist are also studied in detail using Sagdeev’s technique.

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52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Sb	Solitons; BGK modes
52.65.Kj	Magnetohydrodynamic and fluid equation
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Coupling of Alfvén and sound waves in stellarator plasmas

Axel Könies and Denis Eremin

Phys. Plasmas 17, 012107 (2010); http://dx.doi.org/10.1063/1.3274921 (7 pages) | Cited 6 times

Online Publication Date: 26 January 2010

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Recently, a low frequency mode possibly driven unstable by hot electrons [ J. M. Canik et al., 21st IAEA Fusion Energy Conference, Chengdu (China) (IAEA, Vienna, 2006), CN-149EX/5-2 ] has been observed in the Helically Symmetric Experiment [ F. S. B. Anderson et al., Fusion Technol. 27, 273 (1995) ]. The emergence of such a mode has been investigated within the framework of computational three-dimensional magnetohydrodynamics (MHD). A three-dimensional MHD continuum code CONTI has been developed for a fast computation of the continuous Alfvén and sound spectrum. The global modes have been calculated using the CAS3D code. A possibly new class of modes has been identified which is generated by the interaction between sound and Alfvén waves. The respective gap still contains a continuum branch, so that because of the continuum interaction, a conclusive answer if these modes really exist cannot be achieved within the computational ideal MHD picture. Additionally, continuum gaps of similar type have been investigated also for other stellarators.

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52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.65.Kj	Magnetohydrodynamic and fluid equation
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.55.Jd	Magnetic mirrors, gas dynamic traps

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Beta-induced Alfvén-acoustic eigenmodes in stellarator plasmas with low shear

D. Yu. Eremin and A. Könies

Phys. Plasmas 17, 012108 (2010); http://dx.doi.org/10.1063/1.3277261 (12 pages) | Cited 6 times

Online Publication Date: 26 January 2010

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The coupling of low-frequency Alfvénic modes with acoustic oscillations due to curvature of the background magnetic field is considered for stellarator plasmas with low shear. Magnetohydrodynamic (MHD) analysis demonstrates that the interaction between these branches can generate gaps in the continua with a width proportional to beta as well as the magnitude of the Fourier harmonics of the magnetic field strength which cause the coupling. The gaps can provide a habitat for beta-induced Alfvén-acoustic eigenmodes (BAAEs). Using the causality principle, a technique is developed to resolve the singular behavior of the MHD BAAE eigenmode equation at the points of resonance with the acoustic continuum. Alternatively, the singularities arising in the reduced MHD description can be resolved by accounting for the finite parallel electrical field. Both approaches yield consistent continuum damping rate, which proves to be small. Numerical calculations for analytically fitted experimental profiles of electron-dominated plasma in Helically Symmetric eXperiment (HSX) facility yield two weakly damped BAAE modes with different frequencies: one is close to the maximum of the lower-frequency Alfvén-acoustic continuum, and the other is located well within the BAAE gap. The numerically found BAAEs have frequencies in the same range as the experimentally observed electromagnetic modes in HSX, even when the finite diamagnetic frequency effects are considered.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.55.Jd	Magnetic mirrors, gas dynamic traps
52.65.Kj	Magnetohydrodynamic and fluid equation

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Energy release and transfer in guide field reconnection

J. Birn and M. Hesse

Phys. Plasmas 17, 012109 (2010); http://dx.doi.org/10.1063/1.3299388 (11 pages) | Cited 1 time

Online Publication Date: 26 January 2010

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Properties of energy release and transfer by magnetic reconnection in the presence of a guide field are investigated on the basis of 2.5-dimensional magnetohydrodynamic (MHD) and particle-in-cell (PIC) simulations. Two initial configurations are considered: a plane current sheet with a uniform guide field of 80% of the reconnecting magnetic field component and a force-free current sheet in which the magnetic field strength is constant but the field direction rotates by 180° through the current sheet. The onset of reconnection is stimulated by localized, temporally limited compression. Both MHD and PIC simulations consistently show that the outgoing energy fluxes are dominated by (redirected) Poynting flux and enthalpy flux, whereas bulk kinetic energy flux and heat flux (in the PIC simulation) are small. The Poynting flux is mainly associated with the magnetic energy of the guide field which is carried from inflow to outflow without much alteration. The conversion of annihilated magnetic energy to enthalpy flux (that is, thermal energy) stems mainly from the fact that the outflow occurs into a closed field region governed by approximate force balance between Lorentz and pressure gradient forces. Therefore, the energy converted from magnetic to kinetic energy by Lorentz force acceleration becomes immediately transferred to thermal energy by the work done by the pressure gradient force. Strong similarities between late stages of MHD and PIC simulations result from the fact that conservation of mass and entropy content and footpoint displacement of magnetic flux tubes, imposed in MHD, are also approximately satisfied in the PIC simulations.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
52.65.Kj	Magnetohydrodynamic and fluid equation
52.35.Vd	Magnetic reconnection

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Cross-helicity dynamo effect in magnetohydrodynamic turbulent channel flow

Fujihiro Hamba and Masataka Tsuchiya

Phys. Plasmas 17, 012301 (2010); http://dx.doi.org/10.1063/1.3291062 (13 pages)

Online Publication Date: 13 January 2010

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A large eddy simulation of magnetohydrodynamic (MHD) turbulent channel flow is carried out to investigate the dynamo mechanism. It is shown that the streamwise component of the mean magnetic field is generated and sustained due to the effect of the turbulent electromotive force. The Reynolds-averaged turbulence model for MHD flows is assessed; it is suggested that the cross-helicity dynamo effect contributes to the turbulent electromotive force; that is, the electromotive force parallel to the mean vorticity is generated due to the turbulent cross helicity. To verify the importance of the cross-helicity dynamo, the transport equation for the turbulent electromotive force is evaluated; it is confirmed that the term involving the cross helicity and the mean vorticity is the main production term for the turbulent electromotive force. The transport equations for the turbulent kinetic and magnetic energies are also examined to discuss the dynamo mechanism from the viewpoint of the energy transfer.

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52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)
47.65.Md	Plasma dynamos
47.27.-i	Turbulent flows
52.35.Ra	Plasma turbulence
47.60.Dx	Flows in ducts and channels
47.27.nd	Channel flow
52.35.We	Plasma vorticity

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Scaling properties of turbulence driven shear flow

Z. Yan, G. R. Tynan, C. Holland, M. Xu, S. H. Muller, and J. H. Yu

Phys. Plasmas 17, 012302 (2010); http://dx.doi.org/10.1063/1.3276521 (8 pages) | Cited 2 times

Online Publication Date: 13 January 2010

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The characteristics and scaling properties of the turbulence driven shear flow are investigated in a cylindrical laboratory plasma device. For a given plasma pressure, the density fluctuation amplitude and radial particle flux increase with the applied magnetic field. Strong flow shear is found to coexist at high magnetic fields (>700 G) with ∼ 10 kHz drift wave turbulence, but not at low magnetic fields (<700 G). The absolute value of the divergence of the turbulent Reynolds stress at the shear layer is shown to increase with the magnetic field as well. For a fixed magnetic field, the shear flow is found to decrease as the discharge gas pressure is increased. The density fluctuation amplitude and divergence of the turbulent Reynolds stress also decrease with the plasma pressure. For both situations the cross phase between the radial and azimuthal components of the velocity is found to be a key factor to determine variations in the turbulent Reynolds stress at different magnetic fields and discharge pressures. The results show that the generation of the shear flow is related to the development of specific frequency components of the drift wave turbulence for a variety of plasma conditions. The linear stability analysis shows that the observed variation in the turbulence and shear flow with magnetic field is also consistent with a critical gradient behavior.

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52.35.Ra	Plasma turbulence
52.35.Kt	Drift waves
52.25.Gj	Fluctuation and chaos phenomena

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Recurrence quantification analysis of turbulent fluctuations in the plasma edge of Tokamak Chauffage Alfvén Brésilien tokamak

Z. O. Guimarães-Filho, I. L. Caldas, R. L. Viana, I. C. Nascimento, Yu. K. Kuznetsov, and J. Kurths

Phys. Plasmas 17, 012303 (2010); http://dx.doi.org/10.1063/1.3280010 (8 pages) | Cited 3 times

Online Publication Date: 14 January 2010

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Recurrences are close returns of a given state in a time series, and can be used to identify different dynamical regimes and other related phenomena, being particularly suited for analyzing experimental data. In this work, we use recurrence quantification analysis to investigate dynamical patterns in scalar data series obtained from measurements of floating potential and ion saturation current at the plasma edge of the Tokamak Chauffage Alfvén Brésilien [ R. M. O. Galvão et al., Plasma Phys. Controlled Fusion 43, 1181 (2001) ]. We consider plasma discharges with and without the application of radial electric bias, and also with two different regimes of current ramp. Our results indicate that biasing improves confinement through destroying highly recurrent regions within the plasma column that enhance particle and heat transport.

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52.25.Gj	Fluctuation and chaos phenomena
52.55.Fa	Tokamaks, spherical tokamaks
52.80.-s	Electric discharges
52.25.Fi	Transport properties
52.35.Ra	Plasma turbulence

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Gyrokinetic simulations of ion temperature gradient modes in the reversed field pinch

I. Predebon, C. Angioni, and S. C. Guo

Phys. Plasmas 17, 012304 (2010); http://dx.doi.org/10.1063/1.3290173 (7 pages) | Cited 10 times

Online Publication Date: 15 January 2010

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Linear gyrokinetic calculations are applied to the reversed field pinch configuration to investigate the occurrence of ion temperature gradient instabilities. The analysis shows this type of instability to be only marginally responsible for particle and energy transport. The required gradients could be reached only in correspondence to the temperature slopes arising at the boundary of the helical structure in the quasisingle helicity states. The dependence of the instability threshold on the relevant macroscopic quantities is considered. A discussion on the main differences in the driving mechanisms existing between the reversed field pinch and the tokamak configuration is addressed.

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52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Ra	Plasma turbulence
52.65.Tt	Gyrofluid and gyrokinetic simulations

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Dispersion relations of nonlinearly coupled electromagnetic and electrostatic waves in relativistic plasmas

T. C. Pesch and H.-J. Kull

Phys. Plasmas 17, 012305 (2010); http://dx.doi.org/10.1063/1.3292648 (10 pages) | Cited 2 times

Online Publication Date: 19 January 2010

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In the present work large amplitude electromagnetic waves in cold plasmas at relativistic intensities are studied analytically in a plane wave geometry. Special attention is drawn to the nonlinear coupling of electromagnetic and electrostatic modes. In the framework of the Akhiezer–Polovin model, periodic and more general quasiperiodic waves are taken into account. For small densities a two-time-scale method is used to calculate an analytical solution up to the fourth order in the plasma density. Nonlinear dispersion relations are calculated for coupled waves, taking into account the full plasma response for linear as well as for circular polarization. In the presence of a large amplitude electrostatic wave, the results show a major difference from the commonly considered dispersion relation for electromagnetic waves. Finally, the solutions of the Akhiezer–Polovin model are compared with particle-in-cell simulations.

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52.27.Ny	Relativistic plasmas
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.25.-b	Plasma properties

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Effect of magnetic field on temporal development of Rayleigh–Taylor instability induced interfacial nonlinear structure

M. R. Gupta, Labakanta Mandal, Sourav Roy, and Manoranjan Khan

Phys. Plasmas 17, 012306 (2010); http://dx.doi.org/10.1063/1.3293120 (12 pages) | Cited 3 times

Online Publication Date: 26 January 2010

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The effect of magnetic field on the nonlinear growth rate of Rayleigh–Taylor instability induced two fluid interfacial structures has been investigated. The magnetic field is assumed to be parallel to the plane of the two fluid interface and acts in a direction perpendicular to the wave vector. If the magnetic field is restricted only to either side of the interface, the growth rate may be depressed (may almost disappear) or be enhanced depending on whether the magnetic pressure on the interface opposes the instability driving pressure difference g(ρ_h−ρ_l)y or acts in the same direction. If magnetic field is present on both sides of the two fluid interface, stabilization may also take place in the sense that the surface of separation undulates periodically when the force due to magnetic pressure on two sides is such as to act in opposite direction. This result differs from the classical linear theory result which predicts that the magnetic field parallel to the surface has no influence on the growth rate when the wave vector is perpendicular to its direction.

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52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Mw	Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)

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Electromagnetic effects on trace impurity transport in tokamak plasmas

T. Hein and C. Angioni

Phys. Plasmas 17, 012307 (2010); http://dx.doi.org/10.1063/1.3276102 (15 pages) | Cited 8 times

Online Publication Date: 26 January 2010

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The impact of electromagnetic effects on the transport of light and heavy impurities in tokamak plasmas is investigated by means of an extensive set of linear gyrokinetic numerical calculations with the code GYRO [ J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003) ] and of analytical derivations with a fluid model. The impurity transport is studied by appropriately separating diffusive and convective contributions, and conditions of background microturbulence dominated by both ion temperature gradient (ITG) and trapped electron modes (TEMs) are analyzed. The dominant contribution from magnetic flutter transport turns out to be of pure convective type. However it remains small, below 10% with respect to the E×B transport. A significant impact on the impurity transport due to an increase in the plasma normalized pressure parameter β is observed in the case of ITG modes, while for TEM the overall effect remains weak. In realistic conditions of high β plasmas in the high confinement (H-) mode with dominant ITG turbulence, the impurity diffusivity is found to decrease with increasing β in qualitative agreement with recent observations in tokamaks. In contrast, in these conditions, the ratio of the total off-diagonal convective velocity to the diagonal diffusivity is not strongly affected by an increase in β, particularly at low impurity charge, due to a compensation between the different off-diagonal contributions.

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52.25.Fi	Transport properties
52.35.Bj	Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.55.Fa	Tokamaks, spherical tokamaks

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Detection of electric field around field-reversed configuration plasma

Taeko Ikeyama, Masanori Hiroi, Yasunori Ohkuma, and Yasuyuki Nogi

Phys. Plasmas 17, 012501 (2010); http://dx.doi.org/10.1063/1.3280023 (8 pages) | Cited 2 times

Online Publication Date: 6 January 2010

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Electric-field probes consisting of copper plates are developed to measure electric fields in a vacuum region around a plasma. The probes detect oscillating electric fields with a maximum strength of approximately 100 V/m through a discharge. Reproducible signals from the probes are obtained with an unstable phase dominated by a rotational instability. It is found that the azimuthal structure of the electric field can be explained by the sum of an n = 2 mode charge distribution and a convex-surface electron distribution on the deformed separatrix at the unstable phase. The former distribution agrees with that anticipated from the diamagnetic drift motions of plasma when the rotational instability occurs. The latter distribution suggests that an electron-rich plasma covers the separatrix.

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52.70.Ds	Electric and magnetic measurements
52.25.Fi	Transport properties
52.58.Lq	Z-pinches, plasma focus, and other pinch devices
52.35.Qz	Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)
52.35.Fp	Electrostatic waves and oscillations (e.g., ion-acoustic waves)

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Calculating electron cyclotron current drive stabilization of resistive tearing modes in a nonlinear magnetohydrodynamic model

Thomas G. Jenkins, Scott E. Kruger, C. C. Hegna, Dalton D. Schnack, and Carl R. Sovinec

Phys. Plasmas 17, 012502 (2010); http://dx.doi.org/10.1063/1.3276740 (12 pages) | Cited 2 times

Online Publication Date: 7 January 2010

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A model which incorporates the effects of electron cyclotron current drive (ECCD) into the magnetohydrodynamic equations is implemented in the NIMROD code [ C. R. Sovinec et al., J. Comput. Phys. 195, 355 (2004) ] and used to investigate the effect of ECCD injection on the stability, growth, and dynamical behavior of magnetic islands associated with resistive tearing modes. In addition to qualitatively and quantitatively agreeing with numerical results obtained from the inclusion of localized ECCD deposition in static equilibrium solvers [ A. Pletzer and F. W. Perkins, Phys. Plasmas 6, 1589 (1999) ], predictions from the model further elaborate the role which rational surface motion plays in these results. The complete suppression of the (2,1) resistive tearing mode by ECCD is demonstrated and the relevant stabilization mechanism is determined. Consequences of the shifting of the mode rational surface in response to the injected current are explored, and the characteristic short-time responses of resistive tearing modes to spatial ECCD alignments which are stabilizing are also noted. We discuss the relevance of this work to the development of more comprehensive predictive models for ECCD-based mitigation and control of neoclassical tearing modes.

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Show PACS

52.35.Py	Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.65.Kj	Magnetohydrodynamic and fluid equation
52.50.Qt	Plasma heating by radio-frequency fields; ICR, ICP, helicons
52.30.Cv	Magnetohydrodynamics (including electron magnetohydrodynamics)