The effect of the fast-ion profile on Alfvén eigenmode stability

W. W. Heidbrink; M. A. Van Zeeland; M. E. Austin; E. M. Bass; K. Ghantous; N. N. Gorelenkov; B. A. Grierson; D. A. Spong; B. J. Tobias

doi:10.1088/0029-5515/53/9/093006

The effect of the fast-ion profile on Alfvén eigenmode stability

W. W. Heidbrink, M. A. Van Zeeland, M. E. Austin, E. M. Bass, K. Ghantous, N. N. Gorelenkov, B. A. Grierson, D. A. Spong, B. J. Tobias

Plasma Theory and Modeling

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Abstract

Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇β_f in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on- and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.

Original language	English
Article number	093006
Journal	Nuclear Fusion
Volume	53
Issue number	9
DOIs	https://doi.org/10.1088/0029-5515/53/9/093006
State	Published - Sep 2013

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title = "The effect of the fast-ion profile on Alfv{\'e}n eigenmode stability",

abstract = "Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfv{\'e}n eigenmodes (RSAE) and toroidal Alfv{\'e}n eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇βf in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on- and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.",

author = "Heidbrink, {W. W.} and {Van Zeeland}, {M. A.} and Austin, {M. E.} and Bass, {E. M.} and K. Ghantous and Gorelenkov, {N. N.} and Grierson, {B. A.} and Spong, {D. A.} and Tobias, {B. J.}",

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T1 - The effect of the fast-ion profile on Alfvén eigenmode stability

AU - Heidbrink, W. W.

AU - Van Zeeland, M. A.

AU - Austin, M. E.

AU - Bass, E. M.

AU - Ghantous, K.

AU - Gorelenkov, N. N.

AU - Grierson, B. A.

AU - Spong, D. A.

AU - Tobias, B. J.

PY - 2013/9

Y1 - 2013/9

N2 - Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇βf in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on- and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.

AB - Different combinations of on-axis and off-axis neutral beams are injected into DIII-D plasmas that are unstable to reversed shear Alfvén eigenmodes (RSAE) and toroidal Alfvén eigenmodes (TAE). The variations alter the classically expected fast-ion gradient ∇βf in the plasma interior. Off-axis injection reduces the amplitude of RSAE activity an order of magnitude. Core TAEs are also strongly stabilized. In contrast, at larger minor radius, the fast-ion gradient is similar for on- and off-axis injection and switching the angle of injection has a weaker effect on the stability of TAEs. The average mode amplitude correlates strongly with the classically expected profile but the measured profile relaxes to similar values independent of the fraction of off-axis beams. The observations agree qualitatively with a 'critical-gradient' model of fast-ion transport.

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VL - 53

JO - Nuclear Fusion

JF - Nuclear Fusion

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The effect of the fast-ion profile on Alfvén eigenmode stability

Abstract

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