Active control of Alfvén eigenmodes in magnetically confined toroidal plasmas

Abstract

Alfvén waves are electromagnetic perturbations inherent to magnetized plasmas that can be driven unstable by a free energy associated with gradients in the energetic particles' distribution function. The energetic particles with velocities comparable to the Alfvén velocity may excite Alfvén instabilities via resonant wave-particle energy and momentum exchange. Burning plasmas with large population of fusion born super-Alfvénic alpha particles in magnetically confined fusion devices are prone to excite weakly-damped Alfvén eigenmodes (AEs) that, if allowed to grow unabated, can cause a degradation of fusion performance and loss of energetic ions through a secular radial transport. In order to control the fast-ion distribution and associated Alfvénic activity, the fusion community is currently searching for external actuators that can control AEs and energetic ions in the harsh environment of a fusion reactor. Most promising control techniques are based on (i) variable fast-ion sources to modify gradients in the energetic particles' distribution, (ii) localized electron cyclotron resonance heating to affect the fast-ion Plasma Physics and Controlled Fusion

Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

“…Changes in the thermal plasma profiles induced by ECH may affect the AE stability through modifying the driving and damping terms. Such behavior is similar to the ECH effect in tokamaks [4] is due to a combination of mode excitation, damping and eigenmode, which complicates the ECH effect. Further experimental and theoretical study is required to clarify the ECH effect.…”

“…Since these modes enhance the anomalous transport of EP and induce EP loss, which reduces heating efficiency and damages the first wall, it is important to stabilize and/or control the EP-driven MHD modes. Studies have been made on the physical properties of specific modes, and several external actuators have been proposed and demonstrated in tokamaks and helical devices for controlling and/or stabilizing EP-driven modes [4]. Promising control techniques are based on (i) varying the energetic-ion sources to modify the gradients in the energetic ion-distribution [5][6][7][8][9][10], (ii) localized electron cyclotron heating (ECH) to modify the energetic-ion slowing-down distribution [11][12][13][14][15][16][17][18], (iii) a localized electron cyclotron current drive (ECCD) for modifying the equilibrium [19,20] and (iv) externally applied 3D perturbative magnetic fields for manipulating the energetic-ion distribution and thus the wave drive [21,22].…”

Towards enhanced performance in fusion plasmas via turbulence suppression by MeV ions

“…AEs can contribute to efficient ion heating through the onset of intense zonal flows, providing an improved thermal insulation of the central plasma. Thus, AE activity is not necessarily a phenomenon to be avoided in D-T plasmas, but actually one that could be purposely tailored using external actuators [49]. The identification of this novel type of for turbulence suppression has important implications for fusion research, as it holds promise to enhance the performance of future fusion devices with strong alpha particle heating, and thus could ultimately lead to an accelerated realization of commercial fusion power plants.…”

A fast model to resolve the velocity-space of fast-ion losses detected in ASDEX Upgrade and MAST Upgrade

“…The accomplishment of real-time fast-ion loss velocity-space measurements does not only accelerate the analysis of the FILD data. In future works, this information can be also used as an input to the real-time control of the FILD positioning [14] and the active control of MHD events [15].…”