Experimental signatures of homoclinic tangles in poloidally diverted tokamaks

Evans, T. E.; Roeder, R. K. W.; Carter, J. A.; Rapoport, B. I.; Fenstermacher, M. E.; Lasnier, C. J.

doi:10.1088/1742-6596/7/1/015

Experimental signatures of homoclinic tangles in poloidally diverted tokamaks

Journal Article · Thu Apr 21 00:00:00 EDT 2005 · Journal of Physics. Conference Series

DOI:https://doi.org/10.1088/1742-6596/7/1/015· OSTI ID:836418

Evans, T. E. ^[1]; Roeder, R. K. W. ^[2]; Carter, J. A. ^[3]; Rapoport, B. I. ^[4]; Fenstermacher, M. E. ^[5]; Lasnier, C. J. ^[5]

General Atomics, San Diego, CA (United States)
Cornell Univ., Ithaca, NY (United States)
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Harvard Univ., Cambridge, MA (United States)
Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Small non-axisymmetric perturbations of poloidally diverted tokamaks create edge stochastic magnetic field lines that connect to material surfaces such as those in the divertors. Separatrix structure calculations show that the distribution of stochastic field lines on the vessel walls is closely related to the topology of homoclinic tangles formed in the perturbed system. Since these tangles prescribe how the stochastic fields are organized, they are of significant practical interest in tokamak experiments. Experimental measurements of heat and particle distributions on plasma facing surfaces sometimes show split peak patterns that are consistent with the presence of stochasticity and homoclinic tangles. These split peaks are often observed during locked modes and other types of edge instabilities. They are also observed when perturbation fields from magnetohydrodynamic control coils are pulsed during a plasma discharge. Numerical modeling of the perturbation field from these control coils shows that the homoclinic tangle produced by a coil pulse is not always large enough to produce the splitting patterns observed. Nevertheless, there is a clear correlation between the coil pulses and the appearance of the split profiles. These results suggest the presence of the plasma amplification mechanism that enhances the size of the non-resonant homoclinic tangles.

View Accepted Manuscript (DOE)

Research Organization:: General Atomics, San Diego, CA (United States)

Sponsoring Organization:: USDOE

Grant/Contract Number:: FC02-04ER54698; W-7405-ENG-48

OSTI ID:: 836418

Alternate ID(s):: OSTI ID: 20669319
OSTI ID: 884797

Report Number(s):: GA-A24948

Journal Information:: Journal of Physics. Conference Series, Journal Name: Journal of Physics. Conference Series Vol. 7; ISSN 1742-6588

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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