The role of parallel heat transport in the relation between upstream scrape-off layer widths and target heat flux width in H-mode plasmas of the National Spherical Torus Experiment

Journal Article · Tue Jan 01 04:00:00 EST 2008 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.3043799· OSTI ID:1015029

Ahn, J W ^[1]; Boedo, J. A. ^[1]; Maingi, R. ^[2]; Soukhanovskii, V. A. ^[3]

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1. University of California, San Diego
2. Oak Ridge National Laboratory (ORNL)
3. Lawrence Livermore National Laboratory (LLNL)

he physics of parallel heat transport was tested in the scrape-off layer (SOL) plasma of the National Spherical Torus Experiment [M. Ono , Nucl. Fusion 40, 557 (2000); S. M. Kaye , ibid. 45, S168 (2005)] tokamak by comparing the upstream electron temperature (T-e) and density (n(e)) profiles measured by the midplane reciprocating probe to the heat flux (q(perpendicular to)) profile at the divertor plate measured by an infrared camera. It is found that electron conduction explains the near SOL width data reasonably well while the far SOL, which is in the sheath limited regime, requires an ion heat flux profile broader than the electron one to be consistent with the experimental data. The measured plasma parameters indicate that the SOL energy transport should be in the conduction-limited regime for R-R-sep (radial distance from the separatrix location) < 2-3 cm. The SOL energy transport should transition to the sheath-limited regime for R-R-sep>2-3 cm. The T-e, n(e), and q(perpendicular to) profiles are better described by an offset exponential function instead of a simple exponential. The conventional relation between midplane electron temperature decay length (lambda(Te)) and target heat flux decay length (lambda(q)) is lambda(Te)=7/2 lambda(q), whereas the newly derived relation, assuming offset exponential functional forms, implies lambda(Te)=(2-2.5)lambda(q). The measured values of lambda(Te)/lambda(q) differ from the new prediction by 25%-30%. The measured lambda(q) values in the far SOL (R-R-sep>2-3 cm) are 9-10 cm, while the expected values are 2.7

• Research Organization: Oak Ridge National Laboratory (ORNL)
• Sponsoring Organization: SC USDOE - Office of Science (SC)
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 1015029
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 12 Vol. 15; ISSN 1070-664X
• Country of Publication: United States
• Language: English