Three-dimensional plasma edge turbulence simulations of the Mega Ampere Spherical Tokamak and comparison with experimental measurements

Riva, Fabio Matteo; Militello, Fulvio; Elmore, Sarah; Omotani, John T; Dudson, Ben; Walkden, Nick R

doi:10.1088/1361-6587/ab3561

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Journal article

Three-dimensional plasma edge turbulence simulations of the Mega Ampere Spherical Tokamak and comparison with experimental measurements

Riva, Fabio Matteo ORCID Istituto ricerche solari Aldo e Cele Daccò (IRSOL), Faculty of Informatics, Università della Svizzera italiana Switzerland - United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, United Kingdom
Militello, Fulvio United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, United Kingdom
Elmore, Sarah United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, United Kingdom
Omotani, John T United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, United Kingdom
Dudson, Ben York Plasma Institute, Department of Physics, University of York, United Kingdom
Walkden, Nick R United Kingdom Atomic Energy Authority, Culham Centre for Fusion Energy, Culham Science Centre, United Kingdom

2019

Published in:

Plasma Physics and Controlled Fusion. - 2019, vol. 61, no. 9, p. 095013

English The STORM module of BOUT++ (Easy et al 2014 Phys. Plasmas 21 122515) is generalized to simulate plasma turbulence at the periphery of tokamak devices in diverted configurations and it is used to carry out three-dimensional nonlinear flux-driven simulations in double null configuration with realistic experimental parameters of an L-mode plasma discharge in the Mega Ampere Spherical Tokamak. The reliability of STORM in modeling the scrape-off layer (SOL) plasma dynamics is assessed by comparing the numerical results with experimental measurements from a reciprocating Gundestrup probe and from flush-mounted Langmuir probes. This is the first time that a thorough comparison between experimental measurements and three-dimensional simulations in double null configuration is attempted. It is found that the simulations correctly capture most of the statistical properties of plasma turbulence at the outer mid-plane, whereas ion saturation current and floating potential time-averaged profiles at the outer mid-plane are steeper in the simulations than in the experiment. In particular, it is found that the ion saturation current and floating potential probability distribution functions, as well as the power spectra and several statistical properties of intermittent events in the tokamak SOL, such as the shape, duration and separation of burst events are correctly described by the STORM model. Good qualitative agreement is also obtained for the time-averaged ion saturation current density profiles at the divertor plates. On the other hand, the ion saturation current decay length is approximately 4 times smaller in the numerical results than in the experimental measurements. Additionally, the level of the fluctuations is smaller in the simulations than in the experiment. Finally, possible areas of improvement for the STORM model are identified.

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