Double-resonant fast particle-wave interaction

Schneller, M.; Lauber, Philipp; Brüdgam, M.; Pinches, S. D.; Günter, S.

doi:10.1088/0029-5515/52/10/103019

Cited by 23 publications

(29 citation statements)

References 19 publications

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“…A few years later, Berk et al [7] emphasized the potential importance of intermittent 'avalanche' events, where fast ions transported radially by one mode steepen the gradient elsewhere, destabilizing additional modes. More recently, Schneller et al [8] stressed that fast ions with large orbits can intersect multiple AEs, dramatically altering their transport. In experiment, the first observation of AE-induced damage of the walls was caused by convective losses near the midplane of DIII-D [9].…”

Section: Introductionmentioning

confidence: 99%

Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes

et al. 2017

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Experiments in the DIII-D tokamak show that many overlapping small-amplitude Alfvén eigenmodes (AEs) cause fast-ion transport to sharply increase above a critical threshold in beam power, leading to fast-ion density profile resilience and reduced fusion performance. The threshold is above the AE linear stability limit and varies between diagnostics that are sensitive to different parts of fast-ion phase-space. Comparison with theoretical analysis using the nova and orbit codes shows that, for the neutral particle diagnostic, the threshold corresponds to the onset of stochastic particle orbits due to wave-particle resonances with AEs in the measured region of phase space. The bulk fast-ion distribution and instability behavior was manipulated through variations in beam deposition geometry, and no significant differences in the onset threshold outside of measurement uncertainties were found, in agreement with the theoretical stochastic threshold analysis. Simulations using the 'kick model' produce beam ion density gradients consistent with the empirically measured radial critical gradient and highlight the importance of including the energy and pitch dependence of the fast-ion distribution function in critical gradient models. The addition of electron cyclotron heating changes the types of AEs present in the experiment, comparatively increasing the measured fast-ion density and radial gradient. These studies provide the basis for understanding how to avoid AE transport that can undesirably redistribute current and cause fast-ion losses, and the measurements are being used to validate AE-induced transport models that use the critical gradient paradigm, giving greater confidence when applied to ITER.

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Section: Introductionmentioning

confidence: 99%

Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes

et al. 2017

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“…The relevance of the BoT problem for fusion plasmas research was revived in the 1990's by Berk and Breizman [18][19][20], who proposed it as a paradigmatic model to investigate and understand nonlinear interaction of supra-thermal particles with Alfvén fluctuations [20][21][22][23]. In fact, nonlinear interplay of energetic particles (EPs) with Alfvénic fluctuations (such as Alfvén eigenmodes (AEs), EP modes and drift Alfvén waves [21,22,24,25]) and their consequences for fluctuation induced cross-field transport constitute basic phenomena for thermonuclear plasmas [23,[25][26][27][28][29][30][31][32][33][34][35].…”

Section: Introductionmentioning

confidence: 99%

Mixed Diffusive-Convective Relaxation of a Warm Beam of Energetic Particles in Cold Plasma

Carlevaro¹,

Milovanov

Falessi

et al. 2016

Entropy

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This work addresses the features of fast particle transport in the bump-on-tail problem for varying the width of the fluctuation spectrum, in the view of possible applications to studies of energetic particle transport in fusion plasmas. Our analysis is built around the idea that strongly-shaped beams do not relax through diffusion only and that there exists an intermediate time scale where the relaxations are convective (ballistic-like). We cast this idea in the form of a self-consistent nonlinear dynamical model, which extends the classic equations of the quasi-linear theory to "broad" beams with internal structure. We also present numerical simulation results of the relaxation of a broad beam of energetic particles in cold plasma. These generally demonstrate the mixed diffusive-convective features of supra-thermal particle transport essentially depending on nonlinear wave-particle interactions and phase-space structures. Taking into account the modes of the stable linear spectrum is crucial for the self-consistent evolution of the distribution function and the fluctuation intensity spectrum.

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“…The enhanced fast-ion density gradient (at the boundary) drives the n ¼ 4 mode near r ¼ 0:05 m and the n ¼ À1 mode near r ¼ 0:18 m. This process is similar to the hole-clump creation in the phase space. 45,46 Double-resonant fast particle-wave interactions 47 found in numerical EP simulations of the ASDEX Upgrade discharges may also be relevant to our experiments. Future experiments with the multiple-view ANPA diagnostic may resolve detailed fastion density evolution during the EP-mode excitation process.…”

Section: Summary and Discussionmentioning

confidence: 62%

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

et al. 2014

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Multiple bursty energetic-particle (EP) driven modes with fishbone-like structure are observed during 1 MW tangential neutral-beam injection in a reversed field pinch (RFP) device. The distinguishing features of the RFP, including large magnetic shear (tending to add stability) and weak toroidal magnetic field (leading to stronger drive), provide a complementary environment to tokamak and stellarator configurations for exploring basic understanding of EP instabilities. Detailed measurements of the EP mode characteristics and temporal-spatial dynamics reveal their influence on fast ion transport. Density fluctuations exhibit a dynamically evolving, inboardoutboard asymmetric spatial structure that peaks in the core where fast ions reside. The measured mode frequencies are close to the computed shear Alfv en frequency, a feature consistent with continuum modes destabilized by strong drive. The frequency pattern of the dominant mode depends on the fast-ion species. Multiple frequencies occur with deuterium fast ions compared to single frequency for hydrogen fast ions. Furthermore, as the safety factor (q) decreases, the toroidal mode number of the dominant EP mode transits from n ¼ 5 to n ¼ 6 while retaining the same poloidal mode number m ¼ 1. The transition occurs when the m ¼ 1, n ¼ 5 wave-particle resonance condition cannot be satisfied as the fast-ion safety factor (q fi ) decreases. The fast-ion temporal dynamics, measured by a neutral particle analyzer, resemble a classical predator-prey relaxation oscillation. It contains a slow-growth phase arising from the beam fueling followed by a rapid drop when the EP modes peak, indicating that the fluctuation-induced transport maintains a stiff fast-ion density profile. The inferred transport rate is strongly enhanced with the onset of multiple EP modes. V C 2014 AIP Publishing LLC. [http://dx.

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Double-resonant fast particle-wave interaction

Cited by 23 publications

References 19 publications

Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes

Phase-space dependent critical gradient behavior of fast-ion transport due to Alfvén eigenmodes

Mixed Diffusive-Convective Relaxation of a Warm Beam of Energetic Particles in Cold Plasma

Energetic-particle-driven instabilities and induced fast-ion transport in a reversed field pinch

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