Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

Zweben, S. J.; Terry, J. L.; Stotler, D.P.; Maqueda, R. J.

doi:10.1063/1.4981873

Cited by 84 publications

(85 citation statements)

References 161 publications

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“…The function f parameterizes the ratio of the density of particles in the upper level of the radiative emission to the ground state density times the rate of decay of the upper level. As discussed in a review by Zweben et al (2017), f is handily parameterized by a power law dependence on the electron density and temperature for perturbations around values of n e and T e as f (n e , T e ) ∝ n e α T e β where exponents α and β are specific to the neutral species used for the diagnostics and are anticipated to depend weakly on n e and T e itself. Thus, for small relative fluctuations of n e and T e one can assume α and β to be constant.…”

Section: Methodsmentioning

confidence: 99%

“…The puffed gas atoms are excited by local plasma electrons and emit characteristic line radiation modulated by fluctuations in the local electron density and temperature. This emission is sampled by an optical receiver, such as a fast-framing camera or arrays of avalanche photo diodes (APDs) (Terry et al 2001;Cziegler et al 2010;Fuchert et al 2014;Zweben et al 2017). These receivers are commonly arranged in a two-dimensional field of view and encode the plasma fluctuations in a time series of fluctuating emission data.…”

Section: Introductionmentioning

confidence: 99%

“…2014; Zweben et al. 2017). These receivers are commonly arranged in a two-dimensional field of view and encode the plasma fluctuations in a time series of fluctuating emission data.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer

et al. 2020

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Statistical properties of the scrape-off layer plasma fluctuations are studied in ohmically heated plasmas in the Alcator C-Mod tokamak. For the first time, plasma fluctuations as well as parameters that describe the fluctuations are compared across measurements from a mirror Langmuir probe (MLP) and from gas-puff imaging (GPI) that sample the same plasma discharge. This comparison is complemented by an analysis of line emission time-series data, synthesized from the MLP electron density and temperature measurements. The fluctuations observed by the MLP and GPI typically display relative fluctuation amplitudes of order unity together with positively skewed and flattened probability density functions. Such data time series are well described by an established stochastic framework that models the data as a superposition of uncorrelated, two-sided exponential pulses. The most important parameter of the process is the intermittency parameter, $\gamma = {\tau _{d}} / {\tau _{w}}$ , where ${\tau _{d}}$ denotes the duration time of a single pulse and ${\tau _{w}}$ gives the average waiting time between consecutive pulses. Here we show, using a new deconvolution method, that these parameters can be consistently estimated from different statistics of the data. We also show that the statistical properties of the data sampled by the MLP and GPI diagnostic are very similar. Finally, a synthetic GPI signal using only plasma parameters sampled by the MLP shows qualitatively different fluctuation statistics from the measured GPI signal.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer

et al. 2020

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“…This process is referred to as plasma recycling. Neutral particles can also originate from being injected into the vacuum vessel for fuelling or diagnostic purposes 6,7 . Typical SOL temperatures that are much lower than those of the bulk plasma allow for a significant population of neutrals to exist.…”

Section: Introductionmentioning

confidence: 99%

Plasma particle sources due to interactions with neutrals in a turbulent scrape-off layer of a toroidally confined plasma

et al. 2018

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The conditions in the edge and scrape-off layer (SOL) of magnetically confined plasmas determine the overall performance of the device, and it is of great importance to study and understand the mechanics that drive transport in those regions. If a significant amount of neutral molecules and atoms is present in the edge and SOL regions, those will influence the plasma parameters and thus the plasma confinement. In this paper, it is displayed how neutrals, described by a fluid model, introduce source terms in a plasma drift-fluid model due to inelastic collisions. The resulting source terms are included in a four-field drift-fluid model, and it is shown how an increasing neutral particle density in the edge and SOL regions influences the plasma particle transport across the last-closed-flux-surface. It is found that an appropriate gas puffing rate allows for the edge density in the simulation to be self-consistently maintained due to ionization of neutrals in the confined region.

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“…The light fluctuations, integrated over the full spectrum, are only a proxy for plasma density. The correlation between these two figures is very good only when electron temperature and neutral density fluctuations are negligible [50,51], which has not been demonstrated in the case of HETs. A strictly quantitative analysis of the light emitted by a plasma would then require a calibration, which can be led for example with a Langmuir probe or a full collisional radiative model.…”

Section: Fast Frame Camera Data Acquisitionmentioning

confidence: 83%

Fast Camera Analysis of Plasma Instabilities in Hall Effect Thrusters Using a POD Method under Different Operating Regimes

et al. 2020

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Even after half a century of development, many phenomena in Hall Effect Thrusters are still not well-understood. While numerical studies are now widely used to study this highly non-linear system, experimental diagnostics are needed to validate their results and identify specific oscillations. By varying the cathode heating current, its emissivity is efficiently controlled and a transition between two functioning regimes of a low power thruster is observed. This transition implies a modification of the axial electric field and of the plasma plume shape. High-speed camera imaging is performed and the data are analysed using a Proper Orthogonal Decomposition method to isolate the different types of plasma fluctuations occurring simultaneously. The low-frequency breathing mode is observed, along with higher frequency rotating modes that can be associated to rotating spokes or gradient-induced instabilities. These rotating modes are observed while propagating outside the thruster channel. The reduction of the cathode emissivity beyond the transition comes along with a disappearance of the breathing mode, which could improve the thruster performance and stability.

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Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices

Cited by 84 publications

References 161 publications

Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer

Comparison between mirror Langmuir probe and gas-puff imaging measurements of intermittent fluctuations in the Alcator C-Mod scrape-off layer

Plasma particle sources due to interactions with neutrals in a turbulent scrape-off layer of a toroidally confined plasma

Fast Camera Analysis of Plasma Instabilities in Hall Effect Thrusters Using a POD Method under Different Operating Regimes

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