Phenomenology of Compressional Alfven Eigenmodes

Fredrickson, E.; Gorelenkov, N.N.; Menard, J.E.

doi:10.2172/827942

Cited by 5 publications

(12 citation statements)

References 22 publications

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“…NSTX studies of the subcyclotron emission indicate that the instabilities are usually compressional Alfvén eigenmodes (CAE) [3][4][5], although some of the modes are probably global Alfvén eigenmodes [5]. The phenomenology of CAEs was studied extensively in NSTX [6].…”

Section: Introductionmentioning

confidence: 99%

Observation of compressional Alfvén eigenmodes (CAE) in a conventional tokamak

et al. 2006

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Fast-ion instabilities with frequencies somewhat below the ion cyclotron frequency occur frequently in spherical tokamaks such as the National Spherical Torus Experiment (NSTX). NSTX and the DIII-D tokamak are nearly ideal for fast-ion similarity experiments, having similar neutral beams, fast-ion to Alfvén speed v f /v A , fast-ion pressure, and shape of the plasma but with a factor of two difference in major radius. When DIII-D is operated at low field (0.6 T), compressional Alfvén eigenmode (CAE) instabilities appear that closely resemble the NSTX instabilities. In particular, the mode frequencies, polarization and beam-energy threshold are nearly identical to NSTX. CAE in high-field discharges and emission at cyclotron harmonics are also observed. As on NSTX, the basic stability properties are consistent with the idea that the instability is driven by anisotropy in the fast-ion velocity distribution and is damped predominantly by Landau damping of electrons. The results suggest that these modes might be excited in ITER.

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Section: Introductionmentioning

confidence: 99%

Observation of compressional Alfvén eigenmodes (CAE) in a conventional tokamak

et al. 2006

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“…The spectrum of Alfvén eigenmodes excited by neutral beam fast ions in NSTX exhibit a broad range in frequency and wavelength [8]. A spectrogram of data from a Mirnov coil for a typical beam heated plasma is shown in Fig.…”

Section: Measurements Of Alfvénic Eigenmodesmentioning

confidence: 99%

“…The idea is based on a substantial body of analytic and numerical calculations [1][2][3][4], on experimental observations of thermal ion heating by a drift_Alfvén wave [5][6][7], and on the discovery of a broad spectrum of weakly damped Alfvén eigenmodes on NSTX below the ion cyclotron frequency [8]. The idea is based on a substantial body of analytic and numerical calculations [1][2][3][4], on experimental observations of thermal ion heating by a drift_Alfvén wave [5][6][7], and on the discovery of a broad spectrum of weakly damped Alfvén eigenmodes on NSTX below the ion cyclotron frequency [8].…”

Section: Introductionmentioning

confidence: 99%

Stochastic RF Heating of Thermal Ions

Fredrickson¹,

Phillips²,

Hosea³

et al. 2007

AIP Conference Proceedings

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“…Among the most critical of these issues are the scaling of the electron transport with field and current [21][22][23][24][25], the physics of fast-particles in the lower field of the ST [26][27][28][29][30][31][32][33] and the ability to non-inductively sustain the high-beta ST configuration (see Refs. [34][35][36][37][38][39][40][41][42] for progress towards this goal in NSTX, and Refs.…”

Section: : Introduction and Motivationmentioning

confidence: 99%

Exploration of the equilibrium operating space for NSTX-Upgrade

Gerhardt¹,

André²,

Ménard³

2012

Nucl. Fusion

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This paper explores a range of high-performance equilibrium scenarios achievable with neutral beam heating in the NSTX-Upgrade device (Menard J.E. 2012 Nucl. Fusion 52 083015). NSTX-Upgrade is a substantial upgrade to the existing NSTX device (Ono M. et al 2000 Nucl. Fusion 40 557), with significantly higher toroidal field and solenoid capabilities, and three additional neutral beam sources with significantly larger current-drive efficiency. Equilibria are computed with free-boundary TRANSP, allowing a self-consistent calculation of the non-inductive current-drive sources, the plasma equilibrium and poloidal-field coil currents, using the realistic device geometry. The thermal profiles are taken from a variety of existing NSTX discharges, and different assumptions for the thermal confinement scalings are utilized. The no-wall and ideal-wall n = 1 stability limits are computed with the DCON code. The central and minimum safety factors are quite sensitive to many parameters: they generally increase with large outer plasma-wall gaps and higher density, but can have either trend with the confinement enhancement factor. In scenarios with strong central beam current drive, the inclusion of non-classical fast-ion diffusion raises qmin, decreases the pressure peaking, and generally improves the global stability, at the expense of a reduction in the non-inductive current-drive fraction; cases with less beam current drive are largely insensitive to additional fast-ion diffusion. The non-inductive current level is quite sensitive to the underlying confinement and profile assumptions. For instance, for BT = 1.0 T and Pinj = 12.6 MW, the non-inductive current level varies from 875 kA with ITER-98y,2 thermal confinement scaling and narrow thermal profiles to 1325 kA for an ST specific scaling expression and broad profiles. Scenarios are presented which can be sustained for 8–10 s, or (20–30) τCR, at βN = 3.8–4.5. The value of qmin can be controlled at either fixed non-inductive fraction of 100% or fixed plasma current, by varying which beam sources are used, opening the possibility for feedback control of the current profile. In terms of quantities like collisionality, neutron emission, non-inductive fraction, or stored energy, these scenarios represent a significant performance extension compared with NSTX and other present spherical torii.

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Phenomenology of Compressional Alfven Eigenmodes

Abstract: predicts the observed scaling of the low frequency limit for CAE.

Cited by 5 publications

References 22 publications

Observation of compressional Alfvén eigenmodes (CAE) in a conventional tokamak

Observation of compressional Alfvén eigenmodes (CAE) in a conventional tokamak

Stochastic RF Heating of Thermal Ions

Exploration of the equilibrium operating space for NSTX-Upgrade

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