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Bi-directional Alfvén cyclotron instabilities in the mega-amp spherical tokamak
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Sharapov, S. E. (Sergei E.), Lilley, M. K., Akers, R. J., Ayed, N. Ben, Cecconello, M., Cook, James William S., Cunningham, G. and Verwichte, E. (Erwin) (2014) Bi-directional Alfvén cyclotron instabilities in the mega-amp spherical tokamak. Physics of Plasmas, Volume 21 (Number 8). Article number 082501. doi:10.1063/1.4891322 ISSN 1070-664X.
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WRAP_Verwichte_0370723-px-081215-sharapov_2014_cae_paper.pdf - Accepted Version - Requires a PDF viewer. Download (1635Kb) | Preview |
Official URL: http://dx.doi.org/10.1063/1.4891322
Abstract
Alfvén cyclotron instabilities excited by velocity gradients of energetic beam ions were investigated in MAST experiments with super-Alfvénic neutral beam injection over a wide range of toroidal magnetic fields from ∼0.34 T to ∼0.585 T. In MAST discharges with high magnetic field, a discrete spectrum of modes in the sub-cyclotron frequency range is excited toroidally propagating counter to the beam and plasma current (toroidal mode numbers n < 0). At lower magnetic field ≤0.45 T, a discrete spectrum of Compressional Alfvén Eigenmodes (CAEs) with n > 0 arises, in addition to the modes with n < 0. At lowest magnetic fields, the CAEs with n > 0 become dominant, they are observed in frequency range from ∼250 kHz for n=1 to ∼3.5 MHz for n=15 , well above the on-axis ion cyclotron frequency (∼2.5 MHz). The data is interpreted in terms of normal and anomalous Doppler resonances modified by magnetic drift terms due to inhomogeneity and curvature of the magnetic field. A Hall MHD model is applied for computing the eigenfrequencies and the spatial mode structure of CAEs and a good agreement with the experimental frequencies is found.
| Item Type: | Journal Article | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Subjects: | Q Science > QC Physics | ||||||||
| Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||||||
| Library of Congress Subject Headings (LCSH): | Cyclotron waves, Tokamaks | ||||||||
| Journal or Publication Title: | Physics of Plasmas | ||||||||
| Publisher: | American Institute of Physics | ||||||||
| ISSN: | 1070-664X | ||||||||
| Official Date: | 2014 | ||||||||
| Dates: |
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| Volume: | Volume 21 | ||||||||
| Number: | Number 8 | ||||||||
| Article Number: | Article number 082501 | ||||||||
| DOI: | 10.1063/1.4891322 | ||||||||
| Status: | Peer Reviewed | ||||||||
| Publication Status: | Published | ||||||||
| Access rights to Published version: | Restricted or Subscription Access | ||||||||
| Date of first compliant deposit: | 15 December 2015 | ||||||||
| Date of first compliant Open Access: | 15 December 2015 | ||||||||
| Funder: | Engineering and Physical Sciences Research Council (EPSRC) | ||||||||
| Grant number: | EP/J005967/1 (EPSRC) |
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