Abstract Details
Abstracts
Author: Henry J C Oliver
Requested Type: Poster
Submitted: 2017-03-15 10:47:07
Co-authors: S.E.Sharapov, B.N.Breizman, L.J.Zheng, and JET Contributors
Contact Info:
The University of Texas
2515 Speedway
Austin, Texas 78712
United States
Abstract Text:
Ellipticity-induced Alfvén eigenmodes (EAEs) are normal modes of plasma oscillation that exist within gaps in the shear Alfvén continuum produced by the elliptical shape of magnetic surfaces. Axisymmetric EAEs - EAEs with toroidal mode number n=0 - have been observed in Joint European Torus (JET) D-3He plasmas with deuterium beam ions accelerated with ion cyclotron resonance heating (ICRH). The axisymmetric modes are driven unstable by positive gradients in the energy distribution function of ICRH-heated ions. The MHD code AEGIS is used to confirm the existence of the internal mode and to give an estimate of continuum damping of the mode.
The coupled eigenmode equations for ellipticity-induced Alfvén eigenmodes, obtained from the shear Alfvén equation, give the analytical Alfvén continuum. The eigenmode equation is used to obtain the structure of the n=0 mode. The analytical Alfvén continuum is compared to numerical results. The axisymmetric mode is identified as an EAE because of its position within a gap induced by ellipticity, and the dominance of two poloidal harmonics with poloidal mode numbers m=±1. We present preliminary analytical expressions for linear drive of the mode by energetic particles.
The axisymmetric mode is of particular interest because it is not localised to a specific safety factor (q) value as for other gap modes, and it may be used to diagnose fast particle energy distributions at the mode location.
Comments: