Energetic particle-induced geodesic acoustic modes on DIII-D

Self Cite

A newly-developed Imaging Neutral Particle Analyzer (INPA) in the DIII-D tokamak interrogates phase space occupied by fast ions on multiple different orbit topologies, including passing, stagnation, trapped and potato orbits. Depending on plasma parameters and beam injection geometries, this new INPA system is capable of visualizing distributions of fast ions on the selected orbit topology and its associated orbit topological boundaries. More importantly, the system is able to directly visualize the effective pitch angle scattering ν eff in phase space by measuring fast ions that are scattered across the trapped-passing orbit topological boundaries and from counter-passing orbits to co-passing orbits. It also enables visualization of fast ion confined-loss boundaries and resolves the change of the boundary in phase space, as plasma equilibrium evolves. The key goal of this new INPA system is to directly measure ν eff across phase space induced by drift waves and its interaction with Alfvén eigenmodes, i.e. a key issue towards a future fusion power plant.

Section: Introductionmentioning

confidence: 99%

Visualization of phase-space orbit topological boundary using imaging neutral particle analyzer

Du,

Gonzalez-Martin,

Liu

et al. 2023

Self Cite

“…GAMs can be driven by EPs known as the energetic particle-induced geodesic acoustic modes (EGAMs), which were first theoretically predicted by Fu in 2008 [13] and discovered experimentally almost simultaneously [14]. EGAMs have been observed in nearly all main tokamaks [15][16][17][18][19][20][21] and are generally accepted as providing a new pathway for energy and momentum transfer between EPs and the bulk plasma [22][23][24]. In particular, direct evidence of the EGAMs impact on turbulent transport was reported in 2013 by Zarzoso et al using a flux-driven 5D gyro-kinetic simulation [25].…”

Section: Introductionmentioning

confidence: 99%

Plasma elongation effects on energetic particle-induced geodesic acoustic modes in tokamaks

Chen,

Ren,

M Roach

2024

Plasma elongation effects on energetic particle-induced geodesic acoustic modes (EGAMs) are theoretically investigated by using gyro-kinetic equations and the Miller local equilibrium model. Including an arbitrary elongation κ and a finite radial derivative sκ=r∂rκ/κ, a general EGAM dispersion relation is obtained for an arbitrary energetic particle (EP) distribution. In particular, we obtain analytical EGAM dispersion relations for both the double-shifted Maxwellian distribution and the standard slowing-down distribution of EPs. In both cases, the frequency of the unstable EGAM branch decreases slowly with increasing elongation, while its growth rate decreases rapidly with κ when the ratio of the EP to the bulk ion density, nh/ni ≥ 0.1. These trends agree well with previous GENE and ORB5 simulations [A. Di Siena et al 2018 Nucl. Fusion 58 106014], but differ significantly from the elongation effects on geodesic acoustic modes (GAMs) [Zhe Gao et al 2009 Nucl. Fusion 49 045014]. The portion of the EGAM dispersion relation accounting for the first-order finite-orbit-width shows greater sensitivity to frequency compared to that of GAM, which explains the smaller variations in the frequency of EGAM as κ changes. When the EP number is small (typically, nh/ni≈ 5%) in the double-shifted Maxwellian case, the growth rate of EGAMs first increases with the increasing elongation and then decreases, while it monotonically increases with κ in the slowing-down case. Furthermore, the effects of sκ on EGAMs are similar to the elongation κ effects but weaker.

“…Energetic particles (EPs) pose a significant challenge in magnetic confinement fusion devices, and they arise through heating or through fusion reactions. GAMs can be significantly influenced by EPs, giving rise to energetic particle-induced geodesic acoustic modes (EGAMs) [20][21][22][23][24][25][26]. Fu first theoretically investigated EGAMs [27], revealing an unstable branch with a positive growth rate primarily attributed to the EPwave resonance at ω = ω h t (with the superscript 'h' denoting EPs).…”

Section: Introductionmentioning

confidence: 99%

On the energetic particle-induced geodesic acoustic modes with finite-orbit-width effects

Chen,

Li,

Ren

et al. 2024

This study presents an analytical investigation of energetic particle-induced geodesic acoustic modes (EGAMs) within a gyro-kinetic model, incorporating finite-orbit-width (FOW) effects up to the second order. The inclusion of second-order FOW effects introduces two distinct types of energetic particle-wave resonances, occurring at ω = ω t h and ω = 2 ω t h , respectively, where ω t h denotes the transit frequency of energetic particles (EPs). It is found that two unstable EGAM branches coexist: a low frequency branch (LFB) characterized by 0 < ω LFB < ω t , max h , and a high frequency branch (HFB) marked by ω t , max h < ω HFB < 2 ω t , max h . The instability of LFB primarily arises from the resonance ω = ω t h , mainly introduced by first-order FOW effects. As a result, the instability of LFB always exists regardless of the presence or absence of second-order FOW effects, and is barely modified by these effects. In contrast, the instability of HFB is exclusively attributed to the resonance ω = 2 ω t h induced by second-order FOW effects. Consequently, the HFB exhibits instability in the presence of these effects.