Simulation of the eigenmode spectrum below the Toroidicity-induced Alfvén Eigenmode gap generated by the coupling of Alfvén and slow-magnetosonic waves in tokamaks

Kramer, Gerrit J.; Cheng, Frank C. Z.; Podesta, Mario; Nazikian, Raffi

doi:10.1088/1361-6587/ab9153

Simulation of the eigenmode spectrum below the Toroidicity-induced Alfvén Eigenmode gap generated by the coupling of Alfvén and slow-magnetosonic waves in tokamaks

Journal Article · Tue Jun 16 00:00:00 EDT 2020 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/ab9153· OSTI ID:1617638

^[1]; Cheng, Frank C. Z. ^[1]; ^[1]; ^[1]

Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)

The discrete Alfven Eigenmode spectrum below the TAE frequency is studied for hybrid and sawtooth scenarios in tokamaks whereby the full coupling between the Alfven and slow magnetosonic waves are taken into account. In this frequency regime the ususally applied slow-sound approximation is not valid and modes in this frequency regime were recently called Alfven-Slow Eigenmodes (ASE). For the hybrid scenarios (central q ≈ 2 up to ρ ≈ 0.6) a rich spectrum of eigenmodes was found that depend on the plasma pressure and magnetic shear. It was found that the number of modes below the TAE gap is the highest for weakly reversed q~profiles while the number of modes increases with pressure. For zero central shear q-profiles the number of modes is lower than in the reversed shear case while for the normal shear hybrid q-profiles the number of eigenmode first increased with increasing pressure followed by a decrease in the number of eigenmodes. For plasma scenarios with central q < 1 (sawtoothing plasmas) modes were found outside the q=1 surface that are consistent with observations in contrast to the conventional BAE which located at the q=1 surface. The frequency behaviour of the modes below the TAE gap was studied for a reversed shear q-profile in which q_min was varied and it was found that ASEs increase and/or decrease in frequency as function of q_min thereby emerging from and/or disappearing into the continuum.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC)

Grant/Contract Number:: AC02-09CH11466

OSTI ID:: 1617638

Alternate ID(s):: OSTI ID: 1633818
OSTI ID: 23028785

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 7 Vol. 62; ISSN 0741-3335

Publisher:: IOP ScienceCopyright Statement

Country of Publication:: United States

Language:: English

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