Three-dimensional modeling of beam emission spectroscopy measurements in fusion plasmas

Guszejnov, Dávid; Pokol, Gergö; Pusztai, István; Réfy, D.; Zoletnik, S.; Lampert, M.; Nam, Y. U.

doi:10.1063/1.4764564

Cited by 23 publications

(14 citation statements)

References 16 publications

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“…A fluctuation response simulation has been carried out with the RENATE BES simulator [34] to support the statement about the density perturbation localization for the JET case. The simulation places three dimensional density perturbations along the beam line step-wise, aligned with the magnetic field lines.…”

Section: Appendix B Li-bes Fluctuation Response Modelingmentioning

confidence: 99%

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

Réfy

Solano²,

Vianello³

et al. 2020

Nucl. Fusion

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An H-mode plasma state free of edge-localized mode (ELM), close to the L-H transition with clear density and temperature pedestal has been observed both at the Joint European Torus (JET) and at the ASDEX Upgrade (AUG) tokamaks usually identified by a low frequency (LFO, 1-2 kHz), m=1, n=0 oscillation of the magnetics and the modulation of pedestal profiles. The regime at JET is referred to as M-mode while at AUG as intermediate phase or I-phase. This contribution aims at a comparative analysis of these phenomena in terms of the density and temperature pedestal properties, the magnetic oscillations and symmetries. Lithium beam emission spectroscopy (Li-BES) and reflectometer measurements at JET and AUG show that the M-mode and the I-phase modulates the plasma edge density. A high frequency oscillation of the magnetics and the density at the pedestal is also associated with both the M-mode and the I-phase, and its power is modulated with the LFO frequency. The power modulation happens simultaneously in every Mirnov coil signal where it can be detected. The bursts of the magnetic signals and the density at the pedestal region are followed by the flattening of the density profile, and by a radially outward propagating density pulse in the scrape-off layer (SOL). The analysis of the helium line ratio spectroscopy (He-BES) signals at AUG revealed that the electron temperature is modulated in phase with the density, thus the I-phase modulates the pressure profile gradient. This analysis gave opportunity to compare Li-BES and He-BES density ‡ Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena 2 profiles at different locations suggesting a toroidal and poloidal symmetry of the density modulation. The presented results indicate that the regimes, the AUG I-phase and the JET M-mode, exhibit similar characteristics, which leads to the conclusion that the regimes are likely the same.

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Section: Appendix B Li-bes Fluctuation Response Modelingmentioning

confidence: 99%

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

Réfy

Solano²,

Vianello³

et al. 2020

Nucl. Fusion

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“…However, much further work is required to substantiate the hypothesis above. In KSTAR, the spectrum of edge density fluctuations are measured by beam emission spectroscopy (BES) [24,30] (main vacuum, mid-plane, LFS) in ELM mitigation experiments. increases.…”

Section: Particle Flux and Density Fluctuation Analysis At Mid-plane mentioning

confidence: 99%

ELM mitigation by supersonic molecular beam injection: KSTAR and HL-2A experiments and theory

et al. 2014

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We report recent experimental results from HL-2A and KSTAR on ELM mitigation by supersonic molecular beam injection (SMBI). Cold particle deposition within the pedestal by SMBI is verified in both machines.The signatures of ELM mitigation by SMBI are an ELM frequency increase and ELM amplitude decrease.These persist for an SMBI influence time τI. Here, τI is the time for the SMBI influenced pedestal profile to refill. An increase in f SMBI ELM /f 0 ELM and a decrease in the energy loss per ELM WELM were achieved in both machines. Physical insight was gleaned from studies of density and vφ(toroidal rotation velocity) evolution, particle flux and turbulence spectra, divertor heat load. The characteristic gradients of the pedestal density soften and a change in vφwas observed during a τI time. The spectra of the edge particle flux Г~ < ˜vr˜ne> and density fluctuation with and without SMBI were measured in HL-2A and in KSTAR, respectively. A clear phenomenon observed is the decrease in divertor heat load during the τI time in HL-2A. Similar results are the profiles of saturation current density Jsat with and without SMBI in KSTAR. We note that τI/τp (particle confinement time) is close to ~1, although there is a large difference in individual τI between the two machines. This suggests that τI is strongly related to particle-transport events. Experiments and analysis of a simple phenomenological model support the important conclusion that ELM mitigation by SMBI results from an increase in higher frequency fluctuations and transport events in the pedestal.

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“…The code is written in Interactive Data Language (IDL) and utilizes the atomic physics core of the RENATE BES simulator. 30,31 The atomic physics of the beam can be discussed within the collisional-radiative model. The light profile and the density profile are connected through the rate equations which is a coupled differential equation system.…”

Section: Density Profile Reconstructionmentioning

confidence: 99%

Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system

Réfy

Brix

Gomes

et al. 2018

Review of Scientific Instruments

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Diagnostic alkali atom (e.g., lithium) beams are routinely used to diagnose magnetically confined plasmas, namely, to measure the plasma electron density profile in the edge and the scrape off layer region. A light splitting optics system was installed into the observation system of the lithium beam emission spectroscopy diagnostic at the Joint European Torus (JET) tokamak, which allows simultaneous measurement of the beam light emission with a spectrometer and a fast avalanche photodiode (APD) camera. The spectrometer measurement allows density profile reconstruction with ∼10 ms time resolution, absolute position calculation from the Doppler shift, spectral background subtraction as well as relative intensity calibration of the channels for each discharge. The APD system is capable of measuring light intensities on the microsecond time scale. However ∼100 μs integration is needed to have an acceptable signal to noise ratio due to moderate light levels. Fast modulation of the beam up to 30 kHz is implemented which allows background subtraction on the 100 μs time scale. The measurement covers the 0.9 < ρ < 1.1 range with 6-10 mm optical resolution at the measurement location which translates to 3-5 mm radial resolution at the midplane due to flux expansion. An automated routine has been developed which performs the background subtraction, the relative calibration, and the comprehensive error calculation, runs a Bayesian density reconstruction code, and loads results to the JET database. The paper demonstrates the capability of the APD system by analyzing fast phenomena like pellet injection and edge localized modes.

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Three-dimensional modeling of beam emission spectroscopy measurements in fusion plasmas

Cited by 23 publications

References 16 publications

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

Identity of the JET M-mode and the ASDEX Upgrade I-phase phenomena

ELM mitigation by supersonic molecular beam injection: KSTAR and HL-2A experiments and theory

Sub-millisecond electron density profile measurement at the JET tokamak with the fast lithium beam emission spectroscopy system

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