L-H Transition Initiated by Limit Cycle Oscillation Transition in the Globus-M Tokamak

Abstract

The intermediate mode between the ohmic, or low confinement (L-mode), and the increased confinement (H-mode) regimes, or the so called I-phase, which is characterized by the existence of zonal flows in the form of limit cycle oscillations (LCOs), was observed on the Globus-M tokamak. Depending on the LCO frequency, the I-phase resulted in either a transition to H-mode or back to L-mode. The possibility of L-I-H transition initiation induced by LCOs and the effect of LCO frequency were studied by means of numerical modeling of the density profile evolution, taking into account turbulence suppression by the inhomogeneous radial electric field. The modeling results show that lower LCO frequency could be a factor facilitating the L-H transition, whereas higher frequency LCOs are more likely to cause the backward transition to L-mode. The results are in qualitative agreement with the results of the studies of geodesic acoustic mode (GAM)–initiated L-H transition in the TUMAN-3M tokamak, where a lower GAM frequency was found to be beneficial for L-H transition initiation.

Keywords:

• Tokamak
• H-mode
• L-H transition
• radial electric field
• limit cycle oscillations

Acknowledgments

TUMAN-3M tokamak database operation and analysis is supported by Ioffe Institute State contract 0034-2021-0001. The modeling of TUMAN-3M tokamak scenarios is supported by Russian Science Foundation, project 22-12-00062. Globus-M and Globus-M2 tokamaks database operation and analysis is supported by Ioffe Institute State contract FFUG-2024-0028. The modeling of Globus-M tokamak scenarios is supported by the Russian Science Foundation (project 23-72-00024).

Data Availability Statement

The data that support the findings of this study are available from the corresponding author, A. A. Belokurov, upon reasonable request.

Disclosure Statement

No potential competing interest was reported by the authors.

Additional information

Funding

Funding was provided by Ministry of Science and Higher Education of the Russian Federation (Ioffe Institute State contracts 0034-2021-0001 and FFUG-2024-0028), and the Russian Science Foundation (projects 22-12-00062 and 23-72-00024).