Fast magnetic fluctuation diagnostics for Alfvén eigenmode and magnetohydrodynamics studies at the Joint European Torus

Heeter, R. F.; Fasoli, A.; Ali-Arshad, S.; Moret, J. M.

doi:10.1063/1.1313797

Cited by 31 publications

(46 citation statements)

References 31 publications

(22 reference statements)

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“…As a full end-to-end frequency-dependent calibration exists for the magnetics channels acquired through the KC1F system [38], whereas such calibration is not available for the same pick-up coils when acquired through the CATS system, the latter have been rescaled to match the FFT amplitude of the KC1F data. However, a detection problem exists for the internal fluctuation measurements in that not enough of these data were acquired via the KC1F diagnostic.…”

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

confidence: 99%

“…This gives a value for the minimum measurable magnetic field |δB MEAS | producing at least a one-count signal in the KC1F digitizers around 0.5 mG at 10 kHz and 0.01 mG at 200 kHz. For our error analysis, we use the Poisson statistics to estimate the relative error on the KC1F digitizer count, and the estimated error on the end-to-end transfer function [38]. Accordingly, an error thresholding scheme (via the λ NORM parameter, see the appendix) is set in the SRS calculations for the measured magnetic signal |δB MEAS (ω)| in the drift-wave frequency range, from a minimum value which corresponds to three counts at 10 kHz.…”

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

confidence: 99%

“…These fluctuation data were acquired using the central acquisition and triggering system (the so-called CATS diagnostic [37]) and the KC1F diagnostic system [38]. These two diagnostic systems served different purposes: whereas the CATS system provided concurrent and synchronized acquisition of a very large number of channels (>200, including magnetics, ECE and reflectometry measurements) for short time windows (up to 7, the duration of each one not exceeding 150 ms) and at moderate frequency (up to 250 kHz), the KC1F systems had eight channels (mostly magnetics), which were, however, acquired continuously at 1 MHz over four seconds in all but two (#40365 and #41069) of the discharges analysed here (where the data acquisition time window lasted only one second due to RAM limitations).…”

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

confidence: 99%

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

Testa¹,

Albergante²

2012

Nucl. Fusion

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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.

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

confidence: 99%

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

confidence: 99%

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

confidence: 99%

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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

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“…This value is well below the ITER requirement of |ıB MEAS /B POL | ∼ 10 −4 , as the latter is of similar order to the threshold in mode amplitude that is expected to cause stochastic fast ion transport [3]. Note also that values of |ıB MEAS | ∼ mG are routinely measured by HF pick-up coils in all major tokamaks such as JET [4], ASDEX-U [5], MAST [6], DIII-D [7], JT60U [8], i.e. for modes which are far away from the stochasticity threshold.…”

Section: Introductionmentioning

confidence: 99%

Assessment of the ITER high-frequency magnetic diagnostic set

Testa

Carfantan

Toussaint

et al. 2011

Fusion Engineering and Design

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a b s t r a c tThe ITER high-frequency (HF) magnetic diagnostic system has to provide essential measurements of MHD instabilities with |ıB MEAS /B POL | ∼ 10 −4 (∼1 G) for frequencies up to 2 MHz to resolve toroidal mode numbers (n) in the range |n| = 10 to |n| = 50. A review of the measurement requirements for HF MHD instabilities in ITER was initiated during the TW4 work-program and led to significant interest for physics and real-time control issues in measuring modes with |ıB MEAS | as low as ∼10 −3 G at the position of the sensors, with |n| ≤ 30 and poloidal mode numbers |m| ∼ 2|n| up to |n| ∼ 15, for a frequency range extending up to ∼500 kHz. We have examined the ability of the current ITER design for the individual sensors and the diagnostic system as a whole to meet these needs, and have explored what adjustments to the design (of the individual sensors and/or of the system as a whole) or to the requirements would be needed to meet them when considering different hypothesis for the financial costs and risk management over the ITER life-time. First, we find that the proposed diagnostic layout, with 168 sensors in total, does not meet the more stringent measurement requirements and risk management criteria: these can only be met by a revision of the design requiring 350-500 sensors, depending on different costing and risk management options. Second, we find that the current design for the ITER HF Mirnov-type pick-up coil could be usefully revised.

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“…The electrical characteristics of the prototype HF magnetic sensors have been extracted from the measurement of the coil impedance following the technique described in [7]. For the measurement of the effective and stray area, an Helmholtz coil assembly was used.…”

Section: Prototyping Of the Iter Hf Magnetic Sensormentioning

confidence: 99%

Baseline system design and prototyping for the ITER high-frequency magnetic diagnostics set

Testa

Chavan

Guterl

et al. 2009

2009 23rd IEEE/NPSS Symposium on Fusion Engineering

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This paper reports the mechanical and electrical tests performed for the prototyping of the ITER high-frequency magnetic sensor and the analysis of the measurement performance of this diagnostic. The current design for the sensor is not suitable for manufacturing for ITER due to the high likelihood of breakages of the un-guided tungsten wire during the winding. A number of alternative designs and manufacturing processes have been investigated, with the Low Temperature Co-fired Ceramic technology giving the best results. The measurement performance of the baseline system design for the high-frequency magnetic diagnostic cannot meet the intended ITER requirements due to its intrinsic spatial periodicities.

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Fast magnetic fluctuation diagnostics for Alfvén eigenmode and magnetohydrodynamics studies at the Joint European Torus

Cited by 31 publications

References 31 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

Assessment of the ITER high-frequency magnetic diagnostic set

Baseline system design and prototyping for the ITER high-frequency magnetic diagnostics set

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