Strong<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>E</mml:mi><mml:mi /><mml:mo>×</mml:mo><mml:mi /><mml:mi>B</mml:mi></mml:math>Flow Shear and Reduced Fluctuations in a Reversed-Field Pinch

Chapman, B. E.; Chiang, C. S.; Prager, S. C.; Sarff, J. S.; Stoneking, M. R.

doi:10.1103/physrevlett.80.2137

Cited by 45 publications

(42 citation statements)

References 18 publications

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“…In contrast to sawtooth crashes, the dynamo events occurring during EC discharges originate with the mϭ0 modes, resonant in the edge. 17,18,27 The momentary increase in b rms caused by these events is dominantly mϭ0. Note that these events occur during PPCD discharges as well ͑as will be shown below͒.…”

Section: ϫ3mentioning

confidence: 99%

“…The fluctuation power also increases periodically throughout the EC period. These bursts 17,18 are manifestations of the RFP dynamo, and they will be described more below.…”

Section: ϫ3mentioning

confidence: 99%

“…[16][17][18][19][20][21] This is summarized in Table I, which includes standard discharges for comparison. The improved global particle confinement in all three enhanced confinement cases is evidenced by a decreased particle source rate ͑indicated by neutral hydrogen or deuterium radiation͒ and a line-averaged density that is constant or increasing.…”

Section: Enhanced Confinement and Fluctuation Reductionmentioning

confidence: 99%

“…In the second case, the E؋B flow shear and enhanced confinement occur spontaneously, following sawtooth crashes. 17,18 These discharges exhibit a reduction of both the edge electrostatic fluctuations and the core-resonant, global magnetic fluctuations, and both particle and energy confinement improve.…”

Section: Introductionmentioning

confidence: 99%

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E×B flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

et al. 1998

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Strong E؋B flow shear occurs in the edge of three types of enhanced confinement discharge in the Madison Symmetric Torus ͓Dexter et al., Fusion Technol. 19, 131 ͑1991͔͒ reversed-field pinch. Measurements in standard ͑low confinement͒ discharges indicate that global magnetic fluctuations drive particle and energy transport in the plasma core, while electrostatic fluctuations drive particle transport in the plasma edge. This paper explores possible contributions of E؋B flow shear to the reduction of both the magnetic and electrostatic fluctuations and, thus, the improved confinement. In one case, shear in the E؋B flow occurs when the edge plasma is biased. Biased discharges exhibit changes in the edge electrostatic fluctuations and improved particle confinement. In two other cases, the flow shear emerges ͑1͒ when auxiliary current is driven in the edge and ͑2͒ spontaneously, following sawtooth crashes. Both edge electrostatic and global magnetic fluctuations are reduced in these discharges, and both particle and energy confinement improve.

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Section: ϫ3mentioning

confidence: 99%

“…The fluctuation power also increases periodically throughout the EC period. These bursts 17,18 are manifestations of the RFP dynamo, and they will be described more below.…”

Section: ϫ3mentioning

confidence: 99%

Section: Enhanced Confinement and Fluctuation Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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E×B flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

et al. 1998

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“…Periods of spontaneous improved confinement, which can last up to 20 ms, are also characterized by mϭ0 bursts and a reduction of magnetic fluctuations between bursts. 7,[13][14][15] One burst occurs just as the current drive begins in Fig. 4.…”

Section: Fluctuation Reductionmentioning

confidence: 99%

High confinement plasmas in the Madison Symmetric Torus reversed-field pinch

et al. 2002

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Reduction of core-resonant mϭ1 magnetic fluctuations and improved confinement in the Madison Symmetric Torus ͓Dexter et al., Fusion Technol. 19, 131 ͑1991͔͒ reversed-field pinch have been routinely achieved through control of the surface poloidal electric field, but it is now known that the achieved confinement has been limited in part by edge-resonant mϭ0 magnetic fluctuations. Now, through refined poloidal electric field control, plus control of the toroidal electric field, it is possible to reduce simultaneously the mϭ0 and mϭ1 fluctuations. This has allowed confinement of high-energy runaway electrons, possibly indicative of flux-surface restoration in the usually stochastic plasma core. The electron temperature profile steepens in the outer region of the plasma, and the central electron temperature increases substantially, reaching nearly 1.3 keV at high toroidal plasma current ͑500 kA͒. At low current ͑200 kA͒, the total beta reaches 15% with an estimated energy confinement time of 10 ms, a tenfold increase over the standard value which for the first time substantially exceeds the constant-beta confinement scaling that has characterized most reversed-field-pinch plasmas.

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Laboratory investigation of the boundary layer processes of artificially created ionospheric depletion

Cao

et al. 2014

JGR Space Physics

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Key Points:• We studied the boundary layer processes of ionospheric depletion Abstract In the work, we have experimentally investigated the boundary layer processes of artificially created ionospheric depletions. Those ionospheric depletions were modeled via releasing attachment chemicals, such as SF 6 , CF 4 , and CO 2 , into the ambient plasmas. Boundary layer of width of electric scale length emerged and separated those plasmas into two regions, the ambient plasmas and the negative ions plasmas. In the localized boundary layer, those fluctuations of the electron density and the floating potential were investigated varying with the plasma pressure and the partial pressure of released chemicals. The electron density decreased sharply that yielded steep density gradients ∇n e , and the floating potential increased which generated sheared electron flows. It is found that the magnitude of fluctuating floating potential is proportional to that of the ∇n e . Those fluctuations were analyzed in detail using digital spectra analysis techniques. Vortex-like coherent structures were observed in the fluctuations of electrostatic potentials. These coherent frequencies are sensitive to the mass of the negative ions, and all lie in the lower hybrid range. By comparing the experimental results with theoretical predictions, the modes have been identified as the coherent structures resulting from the electron-ion hybrid instability. Our results are important to study the early phase nonlinear evolution of the ionospheric depletion and also may be applied to the plasma sheet boundary layer in where often encounters the narrow electron density gradients and sheared electron flows.

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StrongE×BFlow Shear and Reduced Fluctuations in a Reversed-Field Pinch

Cited by 45 publications

References 18 publications

E×B flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

E×B flow shear and enhanced confinement in the Madison Symmetric Torus reversed-field pinch

High confinement plasmas in the Madison Symmetric Torus reversed-field pinch

Laboratory investigation of the boundary layer processes of artificially created ionospheric depletion

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