Speaker
Description
Energetic particles (EPs) are essential for plasma heating and current drive in present and future fusion devices, but their confinement can be degraded by Alfvén eigenmodes (AEs) and related instabilities [1]. Developing robust methods for AE control is therefore important for preserving EP confinement and reducing fast-ion losses in reactor-relevant regimes [2]. Recent experiments on the Tokamak à Configuration Variable (TCV) have established flexible fast-ion scenarios with supra-Alfvénic neutral-beam ions, enabling dedicated studies of AE excitation, fast-ion transport, and active control.
This contribution presents recent TCV experiments demonstrating reproducible AE control using electron-cyclotron heating and current drive (ECRH/ECCD) [3,4]. Scenarios with both co- and counter-current neutral beam injection were developed to vary the fast-ion drive and access different AE regimes. In these plasmas, localized ECRH/ECCD was used to modify thermal profiles, magnetic shear, and fast-ion phase-space gradients. The experiments show that AE activity can be strongly reduced, and in some cases fully suppressed, by varying the EC deposition location and current-drive direction.
The observations indicate that AE control in TCV results from the combined action of several mechanisms. Changes in electron temperature and density profiles can modify damping, mode structure, and resonance conditions, while localized ECCD can alter the safety-factor profile and magnetic shear. AE suppression is also correlated with a reduction in fast-ion losses and redistribution, indicating a close coupling between EC actuation, wave stability, and fast-ion transport. Comparative studies in positive and negative triangularity further show that the character of AE activity is sensitive to plasma shape and equilibrium profiles, even when fast-ion confinement is similar during MHD-quiescent phases.
Reliable EP diagnostics are essential for developing such control strategies and assessing their applicability to future burning-plasma devices. In this context, recent observations of ion cyclotron emission (ICE) in TCV neutral-beam-heated plasmas provide a complementary passive diagnostic of energetic ions [5,6]. The ICE system has recently been upgraded with five additional toroidally distributed in-vessel magnetic pickup coils, enabling simultaneous multi-channel measurements and future mode-number-resolved studies of high-frequency EP-driven activity.
Together, these results demonstrate that TCV provides a flexible platform for isolating the mechanisms underlying AE control with ECRH/ECCD, while also advancing the diagnostic capability needed to characterize energetic-particle-driven modes. The findings contribute to the physics basis for active control of EP-driven instabilities and improved fast-ion confinement in future burning-plasma devices.
References
[1] W. W. Heidbrink et al., Phys. Plasmas 9, 2113–2119 (2002).
[2] M. García-Muñoz et al., Plasma Phys. Control. Fusion 61, 054007 (2019).
[3] S. E. Sharapov et al., Plasma Phys. Control. Fusion 60, 014026 (2018).
[4] A. Jansen van Vuuren et al., 30th IAEA Fusion Energy Conference, FEC2025.
[5] K. G. McClements et al., Nucl. Fusion 55, 043013 (2015).
[6] R. Ochoukov et al., EPJ Web of Conferences 346, 03009 (2026).
[7] A. Jansen van Vuuren et al., Nuclear Fusion, submitted.