In a world increasingly facing new challenges at the forefront of plasma scientific research and technological innovation, CNR and ISTP pledge progress and achieve an impact in the integration of research into societal practices and policy

High-frequency reversed-shear Alfvén eigenmodes in fast-ion experiments on JET

Dreval M.; Sharapov S.E.; Kazakov Ye.O.; Ongena J.; Nocente M.; Calado R.; Coelho R.; Ferreira J.; Figueiredo A.; Fitzgerald M.; Garcia J.; Giroud C.; Hawkes N.C.; Kiptily V.G.; Nabais F.; Nave M.F.F.; Weisen H.; Craciunescu T.; Salewski M.; Stancar Z.

Conference: 48th EPS Conference on Plasma Physics, pp. 1 - 4 , Online, Amsterdam timezone , 27 June - 1 July 2022 Year: 2022

Keywords: , , ,
Research Activitie:

A broad range of Alfvén eigenmodes (AEs) was destabilized by fast ions in JET D-3He plasmas heated with the three-ion ICRF scenario [1, 2], see Fig. 1. The observed modes include the toroidicity-induced AEs (TAEs), ellipticity-induced AEs (EAEs), as well as reversed-shear AEs (RSAEs), originating from the presence of a local minimum of the safety factor qmin. Two different types of centrally localized RSAEs were regularly observed during the long-period sawtooth phases in this series of JET experiments [3]. In addition to the low-frequency RSAEs with frequencies below the TAE frequency (f ? 80-180 kHz), also RSAEs with frequencies above the TAE frequency (f ? 330-450 kHz) were destabilized. The high-frequency RSAEs feature the temporal decrease of their frequency as the value of qmin decreases (cf. Fig. 1), opposite to the dynamics of the more often observed low-frequency RSAEs. Such high- frequency RSAEs were previously reported in reversed-shear plasmas in JT-60U heated with negative-ion-based NBI, injecting a large number of passing ions with energies ~400 keV [4]. In this contribution, we report the characteristics of the high-frequency RSAEs in JET experiments, investigated in detail using HELENA, CSCAS and MISHKA codes. The computed radial mode structure is consistent with the experimental mode measurements, using an X-mode reflectometer, a multiline interferometer and soft X-ray diagnostics. Our analysis also shows that the high-frequency RSAE destabilization is mostly caused by passing fast ions with energies of several hundred keV [3]. Although the high- frequency RSAEs are not often seen on JET, these modes could be highly relevant for future ITER and fusion reactors dominated by ~MeV-range energetic ions, including a significant population of passing fast ions.

ID 476600
PRODUCT TYPE Conference Proceeding
LAST UPDATE 2023-01-18T08:44:16Z