Electron Heat Transport Measured in a Stochastic Magnetic Field

Biewer, T. M.; Forest, C. B.; Anderson, J. K.; Fiksel, G.; Hudson, B.; Prager, S. C.; Sarff, J. S.; Wright, John; Brower, D. L.; Ding, W. X.; Terry, S. D.

doi:10.1103/physrevlett.91.045004

Cited by 67 publications

(96 citation statements)

References 21 publications

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“…These tearing modes can create magnetic islands and lead to stochastic field lines and enhanced transport. 13 The observed phenomenon of the sawtooth in an RFP is hypothesized to result in the relaxation of the equilibrium closer to a Taylor state. 4 During these events, 14 toroidal flux increases while poloidal flux decreases.…”

Section: ٌϫBϭb ͑1͒mentioning

confidence: 98%

Measurement of current profile dynamics in the Madison Symmetric Torus

et al. 2004

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The current profile and core magnetic field fluctuation amplitudes in a reversed-field pinch are measured by using a high-resolution polarimetry–interferometry system. This paper presents data showing a redistribution of the current during a sawtooth crash. Also, the core magnetic field fluctuation amplitude is observed to increase at a sawtooth crash consistent with the idea of nonlinearly driven dynamo current. In addition, the parallel current density increases in the outer region of the plasma during auxiliary pulsed parallel current drive. This was expected, as the external application of an edge parallel electric field is designed to flatten the current profile providing an equilibrium closer to the minimum energy Taylor state. However, the current density also increases in the core, relative to standard plasmas. This increase can be explained by a reduction of the dynamo (anti)current drive in the core that should accompany the measured reduction of magnetic fluctuations and by a drop in resistivity caused by the increased confinement of fast electrons.

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Section: ٌϫBϭb ͑1͒mentioning

confidence: 98%

Measurement of current profile dynamics in the Madison Symmetric Torus

et al. 2004

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“…Development of a detailed physics understanding requires spatially and temporally resolved measurements of many plasma parameters. In particular, topics such as energy 3 and momentum 4 transport, the magnetohydrodynamic dynamo ͑ṽ ϫ B ͒, 2 and equilibrium reconstruction 5 require plasma temperature, flow, and magnetic field to be precisely measured.…”

Section: Introductionmentioning

confidence: 99%

Advances in neutral-beam-based diagnostics on the Madison Symmetric Torus reversed-field pinch (invited)

Hartog

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Ennis

et al. 2006

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Innovative charge-exchange recombination spectroscopy (CHERS), motional Stark effect (MSE), and Rutherford scattering diagnostics are now in operation on the Madison Symmetric Torus (MST) reversed-field pinch (RFP). The CHERS diagnostic measures impurity ion flow and temperature, localized to 2 cm with high time resolution (similar to 100 kHz). A spectral MSE diagnostic has been in use for five years, measuring vertical bar B vertical bar down to 0.2 T with high precision (similar to 2 and good time resolution (similar to 100 kHz). The Rutherford scattering diagnostic has demonstrated the robustness of this technique for reliable measurement of majority (D) ion temperature, also with high time resolution. MST is a large RFP (R= 1.5 m, a= 0.52 m) operated at moderate current (I-

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“…The uncertainties in this analysis are substantial ͑see Ref. 20 for details͒ but there are three conclusions to draw. First, the standard RFP is clearly governed by stochastic magnetic transport.…”

Section: A Transition Away From Stochastic Transportmentioning

confidence: 99%

“…20 The temperature profiles measured by Thomson scattering in standard and dynamo-free RFP discharges are shown in Fig. 5͑a͒.…”

Section: A Transition Away From Stochastic Transportmentioning

confidence: 99%

“…In the standard RFP, magnetic fluctuations responsible for current drive have radial components which are large enough to destroy flux surfaces over nearly the entire plasma. 20 Independent observations from several diagnostics ͑and appropriate modeling and theory͒ in the MST indicate that the improved confinement in the dynamo-free RFP is a result of a restoration of flux surfaces. The measurements described below indicate that flux surfaces are restored over much of the plasma volume.…”

Section: Confinement Propertiesmentioning

confidence: 99%

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Dynamo-free plasma in the reversed-field pinch: Advances in understanding the reversed-field pinch improved confinement mode

et al. 2005

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Generation and sustainment of the reversed field pinch ͑RFP͒ magnetic configuration normally relies on dynamo activity. The externally applied electric field tends to drive the equilibrium away from the relaxed, minimum energy state which is roughly described by a flat normalized parallel current density profile and is at marginal stability to tearing modes. Correlated fluctuations of magnetic field and velocity create a dynamo electric field which broadens the parallel current density profile, supplying the necessary edge current drive. These pervasive magnetic fluctuations are also responsible for destruction of flux surfaces, relegating the standard RFP to a stochastic-magnetic transport-limited device. Application of a tailored electric field profile ͑which matches the relaxed current density profile͒ allows sustainment of the RFP configuration without dynamo-driven edge current. The method used to ascertain that a dynamo-free RFP plasma has been created is reported here in detail. Several confinement improvements during the accompanying periods of low magnetic fluctuations are observed. Namely, the magnetic fluctuation level is reduced to the point where stochastic-magnetic transport is no longer the dominant process in the core and nested flux surfaces are restored in the core of the dynamo-free RFP.

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Electron Heat Transport Measured in a Stochastic Magnetic Field

Cited by 67 publications

References 21 publications

Measurement of current profile dynamics in the Madison Symmetric Torus

Measurement of current profile dynamics in the Madison Symmetric Torus

Advances in neutral-beam-based diagnostics on the Madison Symmetric Torus reversed-field pinch (invited)

Dynamo-free plasma in the reversed-field pinch: Advances in understanding the reversed-field pinch improved confinement mode

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