Low-frequency global Alfvén eigenmodes in low-shear tokamaks with trapped energetic ions

2009 ◽  
Vol 16 (9) ◽  
pp. 092502 ◽  
Author(s):  
V. S. Marchenko ◽  
Ya. I. Kolesnichenko ◽  
S. N. Reznik
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Alfven Eigenmodes ◽  
Low Shear

Alfvén cascade eigenmodes above the TAE-frequency and localization of Alfvén modes in D- 3 He plasmas on JET

2021 ◽  
Author(s):  
Mykola Dreval ◽  
Sergei E Sharapov ◽  
Yevgen Kazakov ◽  
Jozef Ongena ◽  
Massimo Nocente ◽  
...  
Keyword(s):  
High Frequency ◽  
Low Frequency ◽  
High Energy ◽  
Negative Ion ◽  
Energetic Ions ◽  
Fast Ions ◽  
Alfven Eigenmodes ◽  
Different Types ◽  
Central Regions ◽  
High Frequency Ac

Abstract Various types of Alfvén Eigenmodes (AEs) have been destabilized by fast ions over a broad frequency range from ~80 kHz to ~700 kHz in a series of JET experiments in mixed D-3He plasmas heated with the three-ion ICRF scenario [M. Nocente et al., Nucl. Fusion 60, 124006 (2020)]. In this paper, we identify the radial localization of AEs using an X-mode reflectometer, a multiline interferometer and soft X-ray diagnostics. The analysis is focused on the most representative example of these measurements in JET pulse #95691, where two different types of Alfvén cascade (AC) eigenmodes were observed. These modes originate from the presence of a local minimum of the safety factor qmin. In addition to ACs with frequencies below the frequency of toroidal Alfvén eigenmodes (TAEs), ACs with frequencies above the TAE frequency were destabilized by energetic ions. Both low- (f ≈80-180 kHz) and high-frequency (f ≈ 330-450 kHz) ACs were localized in the central regions of the plasma. The characteristics of the high-frequency ACs are investigated in detail numerically using HELENA, CSCAS and MISHKA codes. The resonant conditions for the mode excitation are found to be determined by passing ions of rather high energy of several hundred keV and similar to those established in JT-60U with negative-ion-based NBI [M. Takechi et al., Phys. Plasmas 12, 082509 (2005)]. The computed radial mode structure is found to be consistent with the experimental measurements. In contrast to low-frequency ACs observed most often, the frequency of the high-frequency ACs decreases with time as the value of qmin decreases. This feature is in a qualitative agreement with the analytical model of the high-frequency ACs in [B.N. Breizman et al., Phys. Plasmas 10 3649 (2003)]. The high-frequency AC could be highly relevant for future ITER and fusion reactor plasmas dominated by ~ MeV energetic ions, including a significant population of passing fast ions.

Influence of trapped energetic ions on low-frequency magnetohydrodynamic instabilities with reversed shear profile

2021 ◽  
Vol 28 (1) ◽  
pp. 012104
Author(s):  
Baofeng Gao ◽  
Huishan Cai ◽  
Feng Wang ◽  
Xiang Gao ◽  
Yuanxi Wan
Keyword(s):  
Low Frequency ◽  
Energetic Ions ◽  
Reversed Shear

Thermal ion effects on kinetic beta-induced Alfvén eigenmodes excited by energetic ions

2013 ◽  
Vol 20 (3) ◽  
pp. 032505 ◽  
Author(s):  
Longyu Qi ◽  
J. Q. Dong ◽  
A. Bierwage ◽  
Gaimin Lu ◽  
Z. M. Sheng
Keyword(s):  
Energetic Ions ◽  
Alfven Eigenmodes ◽  
Ion Effects

scholarly journals Multiplicity of low-shear toroidal Alfven eigenmodes

1996 ◽  
Author(s):  
J. Candy ◽  
B.N. Breizman ◽  
J.W. Van Dam ◽  
T. Ozeki
Keyword(s):  
Alfven Eigenmodes ◽  
Low Shear

scholarly journals Effect of the electron redistribution on the nonlinear saturation of Alfvén eigenmodes and the excitation of zonal flows

2020 ◽  
Vol 86 (3) ◽  
Author(s):  
A. Biancalani ◽  
A. Bottino ◽  
P. Lauber ◽  
A. Mishchenko ◽  
F. Vannini
Keyword(s):  
Magnetic Field ◽  
Zonal Flow ◽  
Large Aspect Ratio ◽  
Nonlinear Saturation ◽  
Energetic Ions ◽  
Electron Population ◽  
Zonal Flows ◽  
Particle In Cell ◽  
Alfven Eigenmodes ◽  
Reversed Shear

Numerical simulations of Alfvén modes driven by energetic particles are performed with the gyrokinetic (GK) global particle-in-cell code ORB5. A reversed shear equilibrium magnetic field is adopted. A simplified configuration with circular flux surfaces and large aspect ratio is considered. The nonlinear saturation of beta-induced Alfvén eigenmodes (BAE) is investigated. The roles of the wave–particle nonlinearity of the different species, i.e. thermal ions, electrons and energetic ions are described, in particular for their role in the saturation of the BAE and the generation of zonal flows. The nonlinear redistribution of the electron population is found to be important in increasing the BAE saturation level and the zonal flow amplitude.

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