Direct Measurement of the Damping of Toroidicity-Induced Alfvén Eigenmodes

Fasoli, A.; Borba, D.; Bosia, G.; Campbell, D.J.; Dobbing, John; Gormezano, C.; Jacquinot, J.; Lavanchy, P.; Lister, J.B.; Marmillod, P.; Moret, J.M.; Santagiustina, A.; Sharapov, S. E.

doi:10.1103/physrevlett.75.645

Cited by 134 publications

(136 citation statements)

References 17 publications

Supporting

Mentioning

130

Contrasting

Order By: Relevance

“…Furthermore, in all the discharges in the alpha-heating experiment low-n NTMs were present with similar amplitudes in the low-frequency range, between ∼10 and ∼35 kHz. The triangular sweeping waveform seen in figure 9 for #42856 is the signal from the saddle coils, used to measure the damping rate of TAEs in this discharge [52]. Hence, as previously reported in [4], the presence or absence of coherent, current/pressure-driven (low-frequency) and higher frequency fast-ion driven modes can be discounted to explain the anomalous ion heating observed with the αs.…”

Section: Measurements Of the Ion And Electron Drift-wave Turbulence Smentioning

confidence: 78%

“…Hence, knowledge of the noise level in the measurements helps one to determine the optimum value for λ NORM to be used for the analysis of the turbulence data. As an example of this efficient tuning of λ NORM , this quantity is set in the range λ NORM = 0.10 to λ NORM = 0.35 when performing the analysis of the very long time series typical of astronomical and astrophysical measurements [7], then λ NORM = 0.85 to λ NORM = 0.95 when performing in real-time the toroidal mode number decomposition of the frequencydegenerate spectrum of coherent AEs actively driven by an in-vessel antenna system in JET [52,72], so that only the largest component is selected for real-time tracking [73,74], then λ NORM = 0.35 to λ NORM = 0.95 when the same analysis is performed post-pulse, so that effectively all (or a selection of the largest between) the coherent, antenna-driven AEs whose amplitude is well above the background turbulence level are…”

Section: Appendix a The Sparse Representation Methods And The Sparspementioning

confidence: 99%

See 1 more Smart Citation

A phenomenological explanation for the anomalous ion heating observed in the JET alpha-heating experiment of 1997

Testa¹,

Albergante²

2012

Nucl. Fusion

View full text Add to dashboard Cite

In the so-called 'alpha-heating' experiment performed on the JET tokamak during the deuterium-tritium campaign of 1997, the ion temperature was found to be far exceeding (both in absolute value and in its rise time) the level that could have been expected from direct collisional heating by the fusion-born alpha particles themselves and energy equipartition with the electrons. To date, no explanation has been put forward for this long standing puzzle, despite much work having been performed on this subject in the early 2000s.Two analysis methods that have recently become available have been employed to re-analyse these observations of an anomalous ion heating. First, an algorithm based on the sparse representation of signals has been used to analyse magnetic, reflectometry and electron-cyclotron emission measurements of the turbulence spectra in the drift-wave range of frequencies. This analysis has then been complemented with turbulence simulations performed with the GENE code.We find, both experimentally and in the simulations, that the presence of a minority, but sufficiently large, population of fusion-born alpha particles that have not yet fully thermalized stabilizes the turbulence in the ion-drift direction, but practically does not affect the turbulence in the electron-drift direction. We link such stabilization of the ion-drift-wave turbulence to the increase in the ion temperature above the level achieved in similar discharges that did not have (at all or enough) alpha particles. When the fusion-born alpha particles have fully thermalized, the turbulence spectrum in the ion-drift direction reappears at somewhat larger amplitudes, which we link to the ensuing reduction in the ion temperature. This phenomenological dynamics fully corresponds to the actual experimental observations. By taking into account an effect of the alpha particles that had not been previously considered, our new analysis finally presents a phenomenological explanation for the so-far-unexplained anomalous ion heating observed in the JET alpha-heating experiment of 1997.Through the formulation of an empirical criterion for ion-drift-wave turbulence stabilization by fusion-born alpha particles, we also show why similar observations were not made in the other deuterium-tritium experiments run so far in JET and TFTR. This allows assessing the operational domain for this stabilization mechanism for ion-drift-wave turbulence in future burning plasma experiments such as ITER, which may open a new path towards the sustainment of a high energy gain in such forthcoming devices.

show abstract

Section: Measurements Of the Ion And Electron Drift-wave Turbulence Smentioning

confidence: 78%

Section: Appendix a The Sparse Representation Methods And The Sparspementioning

confidence: 99%

A phenomenological explanation for the anomalous ion heating observed in the JET alpha-heating experiment of 1997

Testa¹,

Albergante²

2012

Nucl. Fusion

View full text Add to dashboard Cite

show abstract

“…This expression allows an exact and quick calculation of the excitation n-spectrum without the need to repeat the Fourier calculation for different values of the antenna currents. By fitting the measured transfer function H = H(n, ω) to a rational function as described in [19], one obtains the frequency and damping rate of individual modes. Such a fit is shown for 2 modes of n = ±5 in figure 7.…”

Section: Damping Rate Measurements Of N = 3 − 5 Taesmentioning

confidence: 99%

“…is constructed from the input data, as described in [19]. The input data are synchronously detected signals.…”

Section: Real-time N-decomposition Of the Plasma Response Using Sparspecmentioning

confidence: 99%

Optimization of the active MHD spectroscopy system on JET for the excitation of individual intermediate and high-n Alfvén eigenmodes

et al. 2010

Self Cite

View full text Add to dashboard Cite

Abstract. The stability of Alfvén eigenmodes (AEs) is studied experimentally in the JET tokamak by observing the plasma response to antenna-driven frequency-sweeping perturbations at the plasma edge. During the 2008/9 experimental campaigns, the complete set of the new antennas was operated and AEs with toroidal mode numbers (n) in the intermediate-n range were excited under various plasma conditions. In this paper, we describe the results of the work achieved on the technical aspects of the diagnostic. The antenna currents have been optimized to improve the antenna-plasma coupling. The mode-tracking system has been upgraded for real-time targeting of modes with specific n. As an example of the optimized performance of the diagnostic, the paper concludes with a report on the damping rates of n = 3 − 5 toroidal AEs (TAEs) that were measured dynamically while the background plasma parameters were evolving in time.

show abstract

“…By exciting modes with external antennas in Ohmic plasmas with no fast particle drive, it is possible to isolate the damping from the drive mechanisms. Previous work on JET [7][8][9][10][11] has extensively studied the damping rates of low n = 0, 1, and 2 stable AEs excited with large saddle coils across a broad range of plasma conditions, where they have found a clear dependence of the damping, for example, on plasma shape and edge magnetic shear. The damping rate was found to increase with increased triangularity and elongation consistent with the increased edge magnetic shear.…”

Section: Introductionmentioning

confidence: 99%

Initial active MHD spectroscopy experiments exciting stable Alfvén eigenmodes in Alcator C-Mod

Snipes¹,

Schmittdiel²,

Fasoli³

et al. 2004

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

A pair of toroidally localised in-vessel antennas in Alcator C-Mod were used to excite and detect stable Toroidal Alfvén Eigenmode (TAE) resonances in the frequency range of 400 -500 kHz. By ramping the toroidal field, the plasma TAE frequency was swept through the constant antenna excitation frequency to find a resonance and the width of the resonance was measured to determine the effective damping rate of the mode. The toroidal field and density at the resonances were observed to scale as , as expected for Alfvén eigenmodes. TAE damping rates were measured in both inner wall limited and diverted discharges. The inner wall limited damping rates for these discharges were in the range of 1% < |γ/ω| < 4%. Diverted plasmas, on the other hand, required a very small outer gap between the last closed flux surface (LCFS) and the outboard limiter of less than 1 cm to observe the resonances and the damping rates were then very low with |γ/ω| < 1%.

show abstract

Direct Measurement of the Damping of Toroidicity-Induced Alfvén Eigenmodes

Cited by 134 publications

References 17 publications

A phenomenological explanation for the anomalous ion heating observed in the JET alpha-heating experiment of 1997

A phenomenological explanation for the anomalous ion heating observed in the JET alpha-heating experiment of 1997

Optimization of the active MHD spectroscopy system on JET for the excitation of individual intermediate and high-n Alfvén eigenmodes

Initial active MHD spectroscopy experiments exciting stable Alfvén eigenmodes in Alcator C-Mod

Contact Info

Product

Resources

About