Remarks by Ryan Crocker

Crocker, Ryan

doi:10.1017/s0272503700060948

Cited by 1 publication

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“…Recent DIII-D experiments have been dedicated to the study of sub-cyclotron frequency modes [7,24]. A high-frequency AE with ω = 0.58ω ci (in the lab frame, and ω ≈ 0.6ω ci in the plasma frame) was identified as a GAE based on the Doppler-shifted cyclotron resonance condition, calculated fast ion orbit frequencies and comparison with the SAW dispersion [7].…”

Section: Simulations For Higher B Tor Experiments On Diii-dmentioning

confidence: 99%

“…These experiments have been performed for significantly higher values of B tor = 1.2-2 T compared to NSTX-similarity experiments, however, the normalized values of the observed frequencies were approximately the same ω/ω ci ∼ 0.6. HYM simulations have been performed for experimental shot (shot 172019) [24] with the following plasma and beam parameters: B tor = 1.24 T (on axis), n e = 3.4 × 10 13 cm −3 , T e + T i = 2.3 keV, n b = 0.1 × 10 13 cm −3 , β beam = 0.005, β tot = 0.02 (peak values), and injection energy for deuterium beam ions E = 75 keV. In this shot a dominant mode with frequency f ∼ 5.5 MHz was observed.…”

Section: Simulations For Higher B Tor Experiments On Diii-dmentioning

confidence: 99%

“…The first set of simulations was performed based on previously published plasma and NBI profiles and parameters from the NSTX-similarity experiments on DIII-D [6], where the DIII-D toroidal field was lowered to B tor = 0.6 T to match the normalized beam ion speed to NSTX-like values (v 0 /v A 1). The second set of simulations was performed for higher toroidal field, B tor = 1.24 T, corresponding to more recent DIII-D experiments dedicated to the GAE/CAE study [7,24]. In both cases the simulations show instabilities of shear Alfvén type modes, and their properties are compared with the experimental data and the analytical predictions for the DIII-D plasma and NBI parameters.…”

Section: Introductionmentioning

confidence: 99%

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Application of simulations and theory of sub-cyclotron frequency modes to DIII-D

Белова¹,

Crocker²,

Lestz³

et al. 2022

Nucl. Fusion

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Theoretical and numerical study of Alfvén eigenmodes (AEs) in the sub-cyclotron frequency range explains the observed frequency scaling with beam parameters in experiments across different devices. Global Alfvén (GAEs) and compressional Alfvén eigenmodes (CAEs) are frequently excited during neutral beam injection (NBI) in the National Spherical Torus Experiment (NSTX/NSTX-U), as well as other beam-heated devices such as MAST and DIII-D. These modes are driven unstable through the Doppler shifted cyclotron resonance with the NBI ions and can be excited in ITER due to super-Alfvénic velocities and anisotropy of the fast ion distribution. Numerical models and theory for sub-cyclotron frequency modes, previously developed and used to study the excitation of GAEs/CAEs in the NSTX(-U), have been successfully applied to explain the DIII-D observations. Simulations for DIII-D demonstrate that the modes with ω/ωci ≈ 0.6, previously mis-identified as compressional Alfvén eigenmodes, have shear polarization and should be identified as the GAEs. Simulation results match the observed frequencies and estimated toroidal mode numbers in DIII-D experiments. Good agreement is found between scaling of the experimentally observed GAE frequencies with NBI parameters for NSTX, NSTX-U and DIII-D and scaling predicted by the theory and simulations. The DIII-D simulation results also demonstrate that GAEs can be excited for larger aspect-ratio devices and smaller (sub- Alfvénic) beam injection velocities, therefore they can be unstable in ITER.

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Section: Simulations For Higher B Tor Experiments On Diii-dmentioning

confidence: 99%

Section: Simulations For Higher B Tor Experiments On Diii-dmentioning

confidence: 99%