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

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

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

Cited by 52 publications

(83 citation statements)

References 39 publications

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“…The "AE amplitude" plotted in the figure is the sum of the amplitudes of coherent modes between the geodesic acoustic mode (GAM) and TAE frequencies detected by the electron cyclotron emission (ECE) radiometer diagnostic, 31 using the algorithm described in Ref. 25. The observed behavior differs from the typical critical gradient behavior sketched in Fig.…”

Section: Critical Gradient Behaviormentioning

confidence: 89%

“…Unstable toroidal Alfven eigenmodes (TAE) and reversed-shear Alfven eigenmodes (RSAE) are common. 14 Conditions with multiple unstable AEs occur both in L-mode plasmas during the current ramp 6,14,25 and in H-mode steady-state scenario plasmas with elevated q profiles. 26,27 Fast-ion diagnostics include the volume-averaged neutron rate, 28 which is dominated by beam-plasma reactions in the L-mode plasmas, FIDA diagnostics with oblique sightlines, 29 and solid-state neutral-particle analyzers (NPA) operated in current mode 30 (Fig.…”

Section: Critical Gradient Behaviormentioning

confidence: 99%

“…(Here, the fast-ion distribution function that would occur in the absence of wave-induced transport is termed "classical.") Then, in 2013, 25 an experiment that utilized different combinations of on-axis and off-axis injection reported that, once the AE activity was strongly driven, the FIDA profile was invariant to the heating location ( Fig. 3(a)).…”

Section: Critical Gradient Behaviormentioning

confidence: 99%

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Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold

et al. 2017

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Experiments on the DIII-D tokamak have identified how multiple simultaneous Alfvén eigenmodes (AEs) lead to overlapping wave-particle resonances and stochastic fast-ion transport in fusion grade plasmas [C. S. Collins et al., Phys. Rev. Lett. 116, 095001 (2016)]. The behavior results in a sudden increase in fast-ion transport at a threshold that is well above the linear stability threshold for Alfvén instability. A novel beam modulation technique [W. W. Heidbrink et al., Nucl. Fusion 56, 112011 (2016)], in conjunction with an array of fast-ion diagnostics, probes the transport by measuring the fast-ion flux in different phase-space volumes. Well above the threshold, simulations that utilize the measured mode amplitudes and structures predict a hollow fast-ion profile that resembles the profile measured by fast-ion Dα spectroscopy; the modelling also successfully reproduces the temporal response of neutral-particle signals to beam modulation. The use of different modulated sources probes the details of phase-space transport by populating different regions in phase space and by altering the amplitude of the AEs. Both effects modulate the phase-space flows.

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Section: Critical Gradient Behaviormentioning

confidence: 89%

Section: Critical Gradient Behaviormentioning

confidence: 99%

Section: Critical Gradient Behaviormentioning

confidence: 99%

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Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold

et al. 2017

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“…This paper focuses on the 1 MA current 2 T toroidal field L-mode DIII-D on-axis NBI discharge 146102 of [1]. The safety factor at r/a = 0.0, 0. simulations, in section 3 to follow, did not include any effects of rotational or ExB shear.…”

Section: Experimental and Simulation Profile Parametersmentioning

confidence: 99%

Development and validation of a critical gradient energetic particle driven Alfven eigenmode transport model for DIII-D tilted neutral beam experiments

et al. 2015

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Recent experiments with the DIII-D tilted neutral beam injection (NBI) varying the beam energetic particle (EP) source profiles have provided strong evidence that unstable Alfven eigenmodes (AE) drive stiff EP transport at a critical EP density gradient [Heidbrink et al 2013 Nucl. Fusion 53 093006]. Here the critical gradient is identified by the local AE growth rate being equal to the local ITG/TEM growth rate at the same low toroidal mode number. The growth rates are taken from the gyrokinetic code GYRO. Simulation show that the slowing down beam-like EP distribution has a slightly lower critical gradient than the Maxwellian. The ALPHA EP density transport code [Waltz and Bass 2014 Nucl. Fusion 54 104006], used to validate the model, combines the low-n stiff EP critical density gradient AE mid-core transport with the Angioni et al (2009 Nucl. Fusion 49 055013) energy independent high-n ITG/TEM density transport model controling the central core EP density profile. For the on-axis NBI heated DIII-D shot 146102, while the net loss to the edge is small, about half the birth fast ions are transported from the central core r/a < 0.5 and the central density is about half the slowing down density. These results are in good agreement with experimental fast ion pressure profiles inferred from MSE constrained EFIT equilibria.

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“…Changes in radial mode structure as the frequency evolves are modest. This particular discharge uses off-axis neutral beam injection, which results in relatively weak RSAE drive 43 and minimizes changes in mode structure caused by coupling to other unstable modes. 44 Figure 3 shows a similar sequence of ECE spectra for a downsweeping "fishhook" case.…”

Section: Methodsmentioning

confidence: 99%

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

et al. 2013

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Reversed shear Alfven eigenmodes (RSAEs) usually sweep upward in frequency when the minimum value of the safety factor q min decreases in time. On rare occasions, RSAEs sweep downward prior to the upward sweep. Electron cyclotron emission measurements show that the radial eigenfunction during the downsweeping phase is similar to the eigenfunction of normal, upsweeping RSAEs. V C 2013 AIP Publishing LLC. [http://dx

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

Cited by 52 publications

References 39 publications

Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold

Fast-ion transport by Alfvén eigenmodes above a critical gradient threshold

Development and validation of a critical gradient energetic particle driven Alfven eigenmode transport model for DIII-D tilted neutral beam experiments

Measurements of the eigenfunction of reversed shear Alfvén eigenmodes that sweep downward in frequency

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