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Title: Electron thermal transport within magnetic islands in the reversed-field pinch

Abstract

Tearing mode induced magnetic islands have a significant impact on the thermal characteristics of magnetically confined plasmas such as those in the reversed-field pinch (RFP). New Thomson scattering diagnostic capability on the Madison Symmetric Torus (MST) RFP has enabled measurement of the thermal transport characteristics of islands. Electron temperature (T{sub e}) profiles can now be acquired at 25 kHz, sufficient to measure the effect of an island on the profile as the island rotates by the measurement point. In standard MST plasmas with a spectrum of unstable tearing modes, remnant islands are present in the core between sawtoothlike reconnection events. Associated with these island remnants is flattening of the T{sub e} profile inside the island separatricies. This flattening is characteristic of rapid parallel heat conduction along helical magnetic field lines. In striking contrast, a temperature gradient within an m=1, n=5 island is observed in these same plasmas just after a sawtooth event when the m=1, n=5 mode may briefly come into resonance near the magnetic axis. This suggests local heating and relatively good confinement within the island. Local power balance calculations suggest reduced thermal transport within this island relative to the confinement properties of standard MST discharges between reconnection events.more » The magnetic field and island structure is modeled with three-dimensional nonlinear resistive magnetohydrodynamic simulations (DEBS code) with Lundquist numbers matching those in MST during standard discharges. During improved confinement plasmas with reduced tearing mode activity, temperature fluctuations correlated with magnetic signals are small with characteristic fluctuation amplitudes of order T-tilde{sub e}/T{sub e}approx2%.« less

Authors:
;  [1];  [1];  [1]
  1. Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States)
Publication Date:
OSTI Identifier:
21371200
Resource Type:
Journal Article
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 17; Journal Issue: 5; Other Information: DOI: 10.1063/1.3388374; (c) 2010 American Institute of Physics; Journal ID: ISSN 1070-664X
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ELECTRIC DISCHARGES; ELECTRON TEMPERATURE; FLUCTUATIONS; MAGNETIC CONFINEMENT; MAGNETIC ISLANDS; PLASMA DIAGNOSTICS; PLASMA SIMULATION; REVERSE-FIELD PINCH; SAWTOOTH OSCILLATIONS; TEARING INSTABILITY; TEMPERATURE GRADIENTS; THERMAL CONDUCTION; THOMSON SCATTERING; TOKAMAK DEVICES; CLOSED PLASMA DEVICES; CONFINEMENT; ENERGY TRANSFER; HEAT TRANSFER; INELASTIC SCATTERING; INSTABILITY; MAGNETIC FIELD CONFIGURATIONS; OSCILLATIONS; PINCH EFFECT; PLASMA CONFINEMENT; PLASMA INSTABILITY; PLASMA MACROINSTABILITIES; SCATTERING; SIMULATION; THERMONUCLEAR DEVICES; VARIATIONS

Citation Formats

Stephens, H D, Reusch, J A, Den Hartog, D J, Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, Madison, Wisconsin 53706, Hegna, C C, and Department of Engineering Physics, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706. Electron thermal transport within magnetic islands in the reversed-field pinch. United States: N. p., 2010. Web. doi:10.1063/1.3388374.
Stephens, H D, Reusch, J A, Den Hartog, D J, Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, Madison, Wisconsin 53706, Hegna, C C, & Department of Engineering Physics, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706. Electron thermal transport within magnetic islands in the reversed-field pinch. United States. doi:10.1063/1.3388374.
Stephens, H D, Reusch, J A, Den Hartog, D J, Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, Madison, Wisconsin 53706, Hegna, C C, and Department of Engineering Physics, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706. Sat . "Electron thermal transport within magnetic islands in the reversed-field pinch". United States. doi:10.1063/1.3388374.
@article{osti_21371200,
title = {Electron thermal transport within magnetic islands in the reversed-field pinch},
author = {Stephens, H D and Reusch, J A and Den Hartog, D J and Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, University of Wisconsin-Madison, Madison, Wisconsin 53706 and Hegna, C C and Department of Engineering Physics, University of Wisconsin-Madison, 1500 Engineering Drive, Madison, Wisconsin 53706},
abstractNote = {Tearing mode induced magnetic islands have a significant impact on the thermal characteristics of magnetically confined plasmas such as those in the reversed-field pinch (RFP). New Thomson scattering diagnostic capability on the Madison Symmetric Torus (MST) RFP has enabled measurement of the thermal transport characteristics of islands. Electron temperature (T{sub e}) profiles can now be acquired at 25 kHz, sufficient to measure the effect of an island on the profile as the island rotates by the measurement point. In standard MST plasmas with a spectrum of unstable tearing modes, remnant islands are present in the core between sawtoothlike reconnection events. Associated with these island remnants is flattening of the T{sub e} profile inside the island separatricies. This flattening is characteristic of rapid parallel heat conduction along helical magnetic field lines. In striking contrast, a temperature gradient within an m=1, n=5 island is observed in these same plasmas just after a sawtooth event when the m=1, n=5 mode may briefly come into resonance near the magnetic axis. This suggests local heating and relatively good confinement within the island. Local power balance calculations suggest reduced thermal transport within this island relative to the confinement properties of standard MST discharges between reconnection events. The magnetic field and island structure is modeled with three-dimensional nonlinear resistive magnetohydrodynamic simulations (DEBS code) with Lundquist numbers matching those in MST during standard discharges. During improved confinement plasmas with reduced tearing mode activity, temperature fluctuations correlated with magnetic signals are small with characteristic fluctuation amplitudes of order T-tilde{sub e}/T{sub e}approx2%.},
doi = {10.1063/1.3388374},
journal = {Physics of Plasmas},
issn = {1070-664X},
number = 5,
volume = 17,
place = {United States},
year = {2010},
month = {5}
}