Experimental observations of bifurcated power decay lengths in the near Scrape-Off Layer of ST40 High Field Spherical Tokamak

Experimental observations of bifurcated power decay lengths in the near Scrape-Off Layer of ST40 High Field Spherical Tokamak

The scrape-off layer parallel heat flux decay lengths measured at ST40, a high field, low aspect ratio spherical tokamak, have been observed to bifurcate into two groups. The wide group follows established H-mode scalings (ranging between 2 to 8 mm) while the narrow group falls up to 10 times below...

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Main Authors: X. Zhang, C. Marsden, M. Moscheni, E.N.J. Maartensson, A. Rengle, M. Robinson, T. O’Gorman, H.F. Lowe, E. Vekshina, S. Janhunen, A. Scarabosio, P.F. Buxton, M. Sertoli, M. Romanelli, S.A.M. McNamara, T.K. Gray, N.A. Lopez
Format: Article
Language:English
Published: Elsevier 2024-12-01
Series:Nuclear Materials and Energy
Subjects:
ST40 spherical tokamak
Plasma exhaust
Divertor heat flux
Scrape-off Layer width
Infrared thermography
Online Access:http://www.sciencedirect.com/science/article/pii/S2352179124001959
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Summary:The scrape-off layer parallel heat flux decay lengths measured at ST40, a high field, low aspect ratio spherical tokamak, have been observed to bifurcate into two groups. The wide group follows established H-mode scalings (ranging between 2 to 8 mm) while the narrow group falls up to 10 times below these scalings (between 0.2 and 0.8 mm), being comparable to the ion total Larmor radius rather than the ion poloidal Larmor radius. The heat flux profiles of the latter group can only be described by a multi-exponential function, rather than the single exponential function convoluted with a Gaussian. The onset of the narrow scrape-off layer width is observed to be associated with suppressed magnetic fluctuations, suggesting reduced electromagnetic turbulence levels in the SOL.
ISSN:2352-1791

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