TY - JOUR
T1 - Predictions and observations of low-shear beta-induced shear Alfvén-acoustic eigenmodes in toroidal plasmas
AU - Gorelenkov, N. N.
AU - Berk, H. L.
AU - Fredrickson, E.
AU - Sharapov, S. E.
AU - JET EFDA Contributors, EFDA Contributors
PY - 2007/10/8
Y1 - 2007/10/8
N2 - New global MHD eigenmode solutions arising in gaps in the low frequency Alfvén-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfvén-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfvén-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta < 2 % as well as in NSTX plasmas at relatively high-beta > 20 %. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfvén coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
AB - New global MHD eigenmode solutions arising in gaps in the low frequency Alfvén-acoustic continuum below the geodesic acoustic mode (GAM) frequency have been found numerically and have been used to explain relatively low frequency experimental signals seen in NSTX and JET tokamaks. These global eigenmodes, referred to here as Beta-induced Alfvén-Acoustic Eigenmodes (BAAE), exist in the low magnetic safety factor region near the extrema of the Alfvén-acoustic continuum. In accordance to the linear dispersion relations, the frequency of these modes shifts as the safety factor, q, decreases. We show that BAAEs can be responsible for observations in JET plasmas at relatively low beta < 2 % as well as in NSTX plasmas at relatively high-beta > 20 %. In contrast to the mostly electrostatic character of GAMs the new global modes also contain an electromagnetic (magnetic field line bending) component due to the Alfvén coupling, leading to wave phase velocities along the field line that are large compared to the sonic speed. Qualitative agreement between theoretical predictions and observations are found.
UR - https://www.scopus.com/pages/publications/34848846558
UR - https://www.scopus.com/inward/citedby.url?scp=34848846558&partnerID=8YFLogxK
U2 - 10.1016/j.physleta.2007.05.113
DO - 10.1016/j.physleta.2007.05.113
M3 - Article
AN - SCOPUS:34848846558
SN - 0375-9601
VL - 370
SP - 70
EP - 77
JO - Physics Letters, Section A: General, Atomic and Solid State Physics
JF - Physics Letters, Section A: General, Atomic and Solid State Physics
IS - 1
ER -