Observation of Velocity-Independent Electron Transport in the Reversed Field Pinch

O’Connell, R.; Hartog, D. J. Den; Forest, C. B.; Anderson, J. K.; Biewer, T. M.; Chapman, B. E.; Craig, D.; Fiksel, G.; Prager, S. C.; Sarff, J. S.; Terry, S. D.; Harvey, R. W.

doi:10.1103/physrevlett.91.045002

Cited by 36 publications

(27 citation statements)

References 17 publications

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“…This will decrease the core resistivity and lead to higher currents on axis. Finally, new measurements of hard x-ray flux 30 indicate that the confinement of core runaway electrons increases during PPCD. These electrons can also carry significant amounts of current, leading to a drop in the effective resistivity in the core.…”

Section: B Pulsed Parallel Current Drivementioning

confidence: 97%

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: B Pulsed Parallel Current Drivementioning

confidence: 97%

Measurement of current profile dynamics in the Madison Symmetric Torus

et al. 2004

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“…In Ref. 10, the transport scaling of Eq. ͑2͒ could be experimentally confirmed for standard plasmas; however, "improved confinement" plasmas could be generated where the transport was observed to be independent of the parallel runaway electron velocity, and a reduction in transport from D Ϸ 25 m 2 / s to D Ϸ 3 m 2 / s was observed.…”

Section: Introductory Remarksmentioning

confidence: 99%

Runaway electron transport via tokamak microturbulence

Hauff

Jenko

2009

Physics of Plasmas

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The mechanisms found for the magnetic transport of fast ions in the work of Hauff et al. ͓Phys. Rev. Lett. 102, 075004 ͑2009͔͒ are extended to the diffusion of runaway electrons. Due to their smaller mass and larger energy, they behave strongly relativistically, for which reason the scaling laws defined previously have to be modified. It is found that due to these changes, the regime of constant magnetic transport does not exist anymore, but diffusivity scales with E −1 for magnetic transport, or even with E −2 in the case that finite gyroradius effects become important. It is shown that the modified analytical approaches are able to explain the surprisingly small values found in experiments, although it cannot be excluded that possibly other reduction mechanisms are present at the same time.

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“…Figure 6 is a rigorous measurement and accompanying Fokker-Plank modeling which demonstrates the nature of transport in two different RFP regimes. 24 Shown in black is the hard x-ray flux measured by a CdZnTe detector viewing the core of the standard RFP. There is a small but measureable flux up to about 40 keV but above this energy there is effectively no flux.…”

Section: B Fast Particles Confinedmentioning

confidence: 99%

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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Observation of Velocity-Independent Electron Transport in the Reversed Field Pinch

Cited by 36 publications

References 17 publications

Measurement of current profile dynamics in the Madison Symmetric Torus

Measurement of current profile dynamics in the Madison Symmetric Torus

Runaway electron transport via tokamak microturbulence

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

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