April 4-6

Abstract Details

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Author: Salomon Janhunen
Requested Type: Consider for Invited
Submitted: 2022-03-04 06:29:50

Co-authors: Y. Zhang, M. Barnes, M. Romanelli and the ST40 team

Contact Info:
Tokamak Energy Ltd
173 Brook Dr
Abingdon, Oxfordshir   00000
United Kingdom

Abstract Text:
Spherical tokamaks can potentially exhibit improved confinement properties compared to their large-aspect-ratio counterparts. As such, they have been considered as a lower investment cost approach to commercial fusion. Theoretical understanding of large aspect-ratio tokamaks cannot be directly applied to spherical tokamaks; additional work is needed to improve fidelity of transport models for STs.

Turbulent transport in spherical tokamaks is characterized by instabilities present in finite-β regimes; consequently, electromagnetic fluctuations are of interest. In finite-β regimes the ion temperature gradient instability and trapped electron mode are stabilized, but at sufficiently high β gyrokinetic simulations frequently encounter secular growth of heat and particle fluxes in the so-called “non-zonal transition.” Also, in the ST40 hot ion mode shots beam driven Alfvénic instabilities are present to redistribute fast particles radially, affecting the beam deposition profile. Beam-driven toroidal rotation also affects the impurity density asymmetry on a flux surface in ST40.

We summarize recent advances in these topics and give an overview of present efforts in gyrokinetic modelling of transport for ST40.