Particle Transport Due to Magnetic Fluctuations

Stoneking, M. R.; Hokin, S.; Prager, S. C.; Fiksel, G.; Ji, Hantao; Hartog, D. J. Den

doi:10.1103/physrevlett.73.549

Cited by 82 publications

(65 citation statements)

References 24 publications

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“…At higher frequencies the fluctuation spectrum obeys a power law ͑decaying as Ϫ5/2 ͒ and encompasses higher helicities. 12 In the high-frequency range, the toroidal wave number varies linearly with frequency, with frequencies from 50-200 kHz corresponding to toroidal mode numbers from 30-70. These measurements indicate that even at the edge, magnetic turbulence is dominated by fluctuations whose resonant surface lies well in the core.…”

Section: Methodsmentioning

confidence: 99%

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Ambipolar magnetic fluctuation-induced heat transport in toroidal devices

Terry

Fiksel

et al. 1996

Physics of Plasmas

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The total magnetic fluctuation-induced electron thermal flux has been determined in the Madison Symmetric Torus ͑MST͒ reversed-field pinch ͓Fusion Technol. 19, 131 ͑1991͔͒ from the measured correlation of the heat flux along perturbed fields with the radial component of the perturbed field. In the edge region the total flux is convective and intrinsically ambipolar constrained, as evidenced by the magnitude of the thermal diffusivity, which is well approximated by the product of ion thermal velocity and the magnetic diffusivity. A self-consistent theory is formulated and shown to reproduce the experimental results, provided nonlinear charge aggregation in streaming electrons is accounted for in the theory. For general toroidal configurations, it is shown that ambipolar constrained transport applies when remote magnetic fluctuations ͑i.e., global modes resonant at distant rational surfaces͒ dominate the flux. Near locations where the dominant modes are resonant, the transport is nonambipolar. This agrees with the radial variation of diffusivity in MST. Expectations for the tokamak are also discussed.

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Section: Methodsmentioning

confidence: 99%

“…5,12 The particle flux ⌫ e was obtained using an electrostatic energy analyzer in conjunction with a magnetic probe to correlate the parallel electron current fluctuation with B r . The heat flux Q e was obtained with a fast pyrobolometer and magnetic probe to correlate the fluctuating parallel heat flux with B r .…”

Section: Methodsmentioning

confidence: 99%

Ambipolar magnetic fluctuation-induced heat transport in toroidal devices

Terry

Fiksel

et al. 1996

Physics of Plasmas

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“…The typical drift parameter can be estimated to be on the order of 0.2-0.3 based on the observation of current carrying fast electrons [Stoneking et al, 1994] or the measured j k , n, and T e . Using typical parameters [Ji, Prager, and Sar, 1995] in MST (Madison Symmetrical Torus) plasmas as we shall mention in the next section, i.e., B T = 2kG, n = 1 10 19 =m 3 , T e = 100eV, and the plasma radius a = 0 : 5m, we h a v e =a(1:5-2:5) 10 3 .…”

Section: Eects Of Reconnection On Helicity Conservationmentioning

confidence: 99%

Helicity, Reconnection, and Dynamo Effects

2013

Magnetic Helicity in Space and Laboratory Plasmas

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The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo eects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly aects the reconnection rate as well as the shape of the diusion region. Conversely, magnetic reconnection events also strongly aect the global helicity, resulting in ecient helicity cancellation (but not dissipation) during counter-helicity reconnection and a nite helicity increase or decrease (but less eciently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo eects. The turbulent electromotive force along the mean magnetic eld (-eect), due to either electrostatic turbulence or the electron diamagnetic eect, transports mean-eld helicity across space without dissipation. This has been supported by direct measurements of helicity ux in a laboratory plasma. When the dynamo eect is driven by electromagnetic turbulence, helicity in the turbulent eld is converted to mean-eld helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery eect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

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“…1͒ and an insertable Rogowskii coil probe 20 ͑with the outer diameter of 3 cm͒ which measures the local poloidal ͑parallel͒ current. Each version of the complex probe consists of two triple probes to measure electron temperature T e , density n, and floating potential V f at two locations separated by 1.27 cm toroidally ͑in the toroidal version͒ or 0.25 cm radially ͑in the radial version.͒ The toroidal version of the complex probe has been modified to block the fast electrons [21][22][23] from the tungsten or molybdenum tips with a small boron nitride obstacle while the radial version has been aligned so that the tips face away from fast electrons. Thus the fast electron effects on probe measurements are eliminated for the entire range of density.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Measurement of the dynamo effect in a plasma

Prager

Almagri

et al. 1996

Physics of Plasmas

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A series of detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line ͑the ␣ effect͒ arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E؋B drift and electron diamagnetic drift. The three major findings are the following: ͑1͒ The ␣ effect accounts for the dynamo current generation, even in the time dependence through a ''sawtooth'' cycle; ͑2͒ at low collisionality the dynamo is explained primarily by the widely studied pressureless magnetohydrodynamic ͑MHD͒ model, i.e., the fluctuating velocity is dominated by the E؋B drift; ͑3͒ at high collisionality, a new ''diamagnetic dynamo'' is observed, in which the fluctuating velocity is dominated by the electron diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying Taylor's ͓Phys. Rev. Lett. 33, 1139 ͑1974͒; Rev. Mod. Phys. 58, 741 ͑1986͔͒ conjecture.

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Particle Transport Due to Magnetic Fluctuations

Cited by 82 publications

References 24 publications

Ambipolar magnetic fluctuation-induced heat transport in toroidal devices

Ambipolar magnetic fluctuation-induced heat transport in toroidal devices

Helicity, Reconnection, and Dynamo Effects

Measurement of the dynamo effect in a plasma

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