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Description
Sawtooth oscillations and the associated fast ion transport play a critical role in plasma stability, heating efficiency, and fusion performance. Despite general similarities, sawteeth show a broad variance in characteristics, such as sawtooth crash time, amplitude, and period, depending on the safety factor q, plasma current, plasma beta, plasma shape, and collisionality. The improved diagnostics, especially Imaging Neutral Particle Analyzers (INPAs) and Imaging Fast-Ion D-Alpha (IFIDA) fast-ion diagnostics, enable a more refined study of sawteeth dynamics and their impact on fast-ion transport in phase space. An empirical sawtooth database has been built to characterize sawtooth behavior and quantify the resulting fast-ion transport. The database confirms the general observation that passing fast ions are often redistributed by sawteeth from the plasma core to regions outside the q=1 surface, leading to reductions in central fast-ion density of up to 30% in the core. In contrast, trapped fast ions are only weakly affected, with relative changes typically below 10%. TRANSP-NUBEAM module, gyro-fluid FAR3d code, and hybrid MHD-kinetic CLT-K code have been applied to model sawtooth-induced fast ion transport across a few dedicated and different classes of sawteeth. For sawteeth with fast crash time, the FAR3d and CLT-K simulation results show a reduction in core fast-ion density and primarily in passing fast ion population, which aligns with experimental data. Both experimental and modeling results will be quantitatively compared with Kolesnichenko’s theory [1,2] of sawtooth–fast ion interactions to validate the model.
ACKNOWLEDGEMENTS: This work was supported in part by the US Department of Energy under DE-SC0020337, DE-FC02-04ER54698, DE-FG02-04ER54742
REFERENCE:
[1] Ya. I. Kolesnichenko, V. V. Lutsenko, Yu. V. Yakovenko, G. Kamelander Phys. Plasmas 4, 2544–2554 (1997)
[2] Ya.I. Kolesnichenko, V.V. Lutsenko, R.B. White, Yu.V. Yakovenko Nucl. Fusion 40 1325 (2000)