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

Journal Article · Sat May 15 00:00:00 EDT 2010 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3388374· OSTI ID:21371200

Stephens, H D; Reusch, J A ^[1]; Den Hartog, D J ^[1]; Hegna, C C ^[1]

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1. Department of Physics, University of Wisconsin-Madison, 1150 University Ave., Madison, Wisconsin 53706 (United States)

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%.

• OSTI ID: 21371200
• Journal Information: Physics of Plasmas, Vol. 17, Issue 5; Other Information: DOI: 10.1063/1.3388374; (c) 2010 American Institute of Physics; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

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