Speaker
Description
To obtain high fusion performance and satisfy the first wall material limit in future fusion devices, increasing effort has been made to develop and investigate high-confinement no-ELM (Edge Localized Mode) and small-ELM scenarios. Among them, recently, the X-point radiator (XPR) regime has been developed in multiple devices, including the TCV tokamak, and shows promising ELM suppression [1,2]. However, relatively little is known about fluctuations and filamentary turbulence at the plasma edge and first-wall for this scenario. In this work, we will present recent experimental observation in TCV to explore the dynamics of the edge and SOL fluctuations in the XPR regime, using Gas Puff Imaging (GPI) and other diagnostics including wall-embedded Langmuir probes, reciprocating probes, bolometry and high-speed cameras [3]. Specifically, we will characterize and compare fluctuations, filament properties, and far-SOL transport in Type-I ELMy and ELM-free phases, at the outboard midplane and X-point. In the Snowflake XPR ELM-free H-mode, a periodic burst in the plasma edge is captured by the midplane and X-point GPI, potentially representing the mechanism replacing the particle transport channel otherwise provided by ELMs. In more recent experiments, an ELM suppression was obtained via nitrogen seeding in NBI and ECRH heated single null plasmas, and a gradual reduction in ELM amplitude was observed in the transition to the ELM-free phase. The general fluctuation features of filamentary turbulence and bursts in this regime will be presented.
[1] M. Bernert et al. 2021 Nucl. Fusion 61 024001
[2] H. Reimerdes et al. 2024 Nuclear Materials and Energy Volume 41, 101784
[3] N. Offeddu, C. Wüthrich, W. Han, et al. 2022 Rev. Sci. Instrum. 93, 123504