Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model

dc.affiliation.dptoUC3M. Departamento de Físicaes
dc.affiliation.grupoinvUC3M. Grupo de Investigación: Física de Plasmases
dc.contributor.authorVarela, Jacobo
dc.contributor.authorSpong, Donald
dc.contributor.authorGarcía Gonzalo, Luis
dc.contributor.funderMinisterio de Economía y Competitividad (España)es
dc.description.abstractAlfven Eigenmodes (AE) can be destabilized by energetic particles in neutral beam injection (NBI) heated plasmas through inverse Landau damping and couplings with gap modes in the shear Alfven continua. We describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system using the reduced MHD equations, density and parallel velocity moments for the energetic particles as well as the geodesic acoustic wave dynamics. A closure relation adds the Landau damping and resonant destabilization effects in the model. We apply the model to study the Alfven modes stability in TJ-II, performing a parametric analysis in a range of realistic values of energetic particle beta (beta(f)), ratios of thermal/Alfven velocities (V-th/V-A0), energetic particle density profiles and toroidal modes (n) including toroidal and helical couplings. The study predicts a large helical coupling between different toroidal modes and the destabilization of helical Alfven eigenmodes (HAE) with frequencies similar to the AE activity measured in TJ-II, between 50-400 kHz. The analysis has also revealed the destabilization of GAE (global Alfven eigenmodes), TAE (toroidal Alfven eigenmodes) and EPM (energetic particle modes). For the modes considered here, optimized TJ-II operations require a t profile in the range of [0.845, 0.979] to stabilize AEs in the inner and middle plasma. AEs in the plasma periphery cannot be fully stabilized, although for a configuration with t = [0.945, 1.079], only n = 7, 11, 15 AE are unstable with a growth rate 4 times smaller compared to the standard t = [1.54, 1.68] case and a frequency of 100 kHz. We reproduce the frequency sweeping evolution of the AE frequency observed in TJ-II as the t profile is varied. The AE frequency sweeping is caused by consecutive changes of the instability dominant modes between different helical families.en
dc.description.sponsorshipThis material based on work is supported both by the U.S. Department of Energy, Office of Science, under Contract DE-AC05-00OR22725 with UT-Battelle, LLC. This research was sponsored in part by the Ministerio of Economia y Competitividad of Spain under project no. ENE2015-68265-P. We also want to acknowledge Alexander Melnikov and the TJ-II group at CIEMAT for providing us the initial VMEC equilibria and useful discussions regarding the experimental phenomena.en
dc.identifier.bibliographicCitationVarela, J., Spong, D. & Garcia, L. (2017). Analysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure model. Nuclear Fusion, 57(12), 126019.en
dc.identifier.publicationtitleNuclear Fusionen
dc.publisherIOP Publishingen
dc.relation.projectIDGobierno de España. ENE2015-68265-Pes
dc.rights© 2017 IAEA, Viennaen
dc.rights.accessRightsopen access
dc.subject.otherEnergetic particlesen
dc.titleAnalysis of Alfven eigenmodes destabilization by energetic particles in TJ-II using a Landau-closure modelen
dc.typeresearch article*
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