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dc.contributor.authorLestz, J.B.
dc.contributor.authorBelova, E.V.
dc.contributor.authorGorelenkov, N.N
dc.description.abstractA comprehensive numerical study has been conducted in order to investigate the stability of beam-driven, sub-cyclotron frequency compressional (CAE) and global (GAE) Alfven Eigenmodes in low aspect ratio plasmas for a wide range of beam parameters. The presence of CAEs and GAEs has previously been linked to anomalous electron temperature profile flattening at high beam power in NSTX experiments, prompting further examination of the conditions for their excitation. Linear simulations are performed with the hybrid MHD-kinetic initial value code HYM in order to capture the general Doppler-shifted cyclotron resonance that drives the modes. Three distinct types of modes are found in simulations -- co-CAEs, cntr-GAEs, and co-GAEs -- with differing spectral and stability properties. The simulations reveal that unstable GAEs are more ubiquitous than unstable CAEs, consistent with experimental observations, as they are excited at lower beam energies and generally have larger growth rates. Local analytic theory is used to explain key features of the simulation results, including the preferential excitation of different modes based on beam injection geometry and the growth rate dependence on the beam injection velocity, critical velocity, and degree of velocity space anisotropy. The background damping rate is inferred from simulations and estimated analytically for relevant sources not present in the simulation model, indicating that co-CAEs are closer to marginal stability than modes driven by the cyclotron resonances.en_US
dc.description.tableofcontentsreadme and digital data filesen_US
dc.publisherPrinceton Plasma Physics Laboratory, Princeton Universityen_US
dc.relationNuclear Fusionen_US
dc.subjectFast ion driven instabilitiesen_US
dc.subjectCompressional Alfven Eigenmodesen_US
dc.subjectGlobal Alfven Eigenmodesen_US
dc.subjectHybrid simulationsen_US
dc.subjectDoppler-shifted cyclotron resonanceen_US
dc.titleHybrid simulations of sub-cyclotron compressional and global Alfven Eigenmode stability in spherical tokamaksen_US
dc.contributor.funderU. S. Department of Energyen_US
Appears in Collections:Theory and Computation

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