Edge turbulence scaling in RFX-mod as measured using GPI diagnostic

Scarin, P.; Agostini, M.; Cavazzana, R.; Sattin, F.; Serianni, G.; Spolaore, M.; Vianello, N.

doi:10.1016/j.jnucmat.2009.01.129

Cited by 16 publications

(20 citation statements)

References 29 publications

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“…The dimension of the edge structures b decreases from 60 mm at n e ∼ 1 × 10 19 m −3 down to 15 mm when n e 4 × 10 19 m −3 . Above this density the width of the structures stabilizes and no changes are observable at higher densities [47]. The same behaviour can be found in the dimension of the edge layer: in figure 15 The similarity between the spatial dimension of the edge coherent structures and the width of the edge region is a clear indication of their affiliation.…”

Section: Edge Transportsupporting

confidence: 62%

Characterization of particle confinement properties in RFX-mod at a high plasma current

Auriemma¹,

Lorenzini²,

Agostini³

et al. 2015

Nucl. Fusion

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Transport phenomena affect the performance of fusion devices, reducing heat and particle confinement and consequently leading to a lower fusion triple product and higher fluxes on the plasma facing material. Special attention is devoted in the fusion community to the study of transport mitigation phenomena which lead to the onset of transport barriers in tokamaks, stellarators and reverse field pinch plasmas. The aim of this study is to deepen our understanding of the mechanisms driving transport in the presence of electron internal transport barriers in the RFX-mod single helical axis (SHAx) state (Lorenzini et al 2009 Nature Phys. 5 570). We discuss whether transport in the core can be described within the theory of chaotic transport. Light is also shed on the mechanisms acting at the plasma edge. The particle source is calculated using the 2D Monte-Carlo code NENE, considering the pattern of plasma-wall interaction. In the core region of the SHAx we found that the diffusivity along 90% of the radius is reduced with respect to the standard case: D ∼ 1 m 2 s −1 fits well with the density profile, compared with the ∼50 m 2 s −1 of a standard plasma. This result confirms a strong mitigation of magnetic chaos, although comparison with the neoclassical diffusivity D neo ∼ 0.01-0.4 m 2 s −1 indicates that transport in the SHAx is still anomalous. The same picture describes well both the particle and energy transport in the plasma core: comparison with the effective thermal diffusivity χ eff indicates that the ratio χ eff /D ∼ (m i /m e ) 0.5 is consistent with the theory of chaos-dominated transport.The plasma edge is affected by a different mechanism. In the external region (the final 10% of the radius) magnetic chaos is suppressed and the edge diffusivity is likely to be ruled by electrostatic turbulence, in particular a direct link with the presence of pressure coherent structures is found.

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Section: Edge Transportsupporting

confidence: 62%

Characterization of particle confinement properties in RFX-mod at a high plasma current

Auriemma¹,

Lorenzini²,

Agostini³

et al. 2015

Nucl. Fusion

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“…There, at high density, particles accumulate, radiation increases and the plasma cools down. In RFX-mod at high density, smaller blobs are nested into larger ones, corresponding to more effective coherent structures with higher density [16]. Indeed, also in Tokamaks the high density regimes are characterized by blobs at higher density [21].…”

Section: The Role Of the Edge Flow And Transportmentioning

confidence: 99%

High density physics in reversed field pinches: comparison with tokamaks and stellarators

et al. 2009

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Reversed Field Pinches (RFPs) share with Tokamaks and Stellarators the experimental evidence of an upper limit for the maximum value of the electron density at which they can operate. Above a certain density level, well described by the Greenwald law for Tokamaks and RFPs, a radiative collapse with strong plasma cooling is observed, predominantly due to processes occurring at the plasma boundary. In the RFX-mod RFP close to the density limit a radiating belt, poloidally symmetric and toroidally localized, develops in the region where the plasma is shrunk as an effect of the m=0 tearing modes. The phenomenology recalls that of MARFES or plasma detachment, though, unlike Tokamaks, the appearance of the radiating belt is associated to a soft landing of the plasma discharge. The paper reports the experimental pattern of the RFX-mod plasmas close to the density limit, including density and radiation profiles, plasma flow and turbulence. Particles are toroidally conveyed towards the region of maximum shrinking of the plasma column where they accumulate. The interpretation is related to the topology of MHD m=0 and m=1 modes: the reconstruction of the magnetic topology shows that the highly radiating region corresponds to the presence of peripheral m=0 magnetic islands well detached from the wall. The emerging indication is that in RFPs a reduction of the m=0 activity could be a way to overcome the density limit.

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“…77,79,[95][96][97][98] The light fluctuations seen with GPI were compared with a thermal helium beam line ratio diagnostic of density and temperature fluctuations made using the same helium gas puff. On the TPE-RX field reversed pinch in Japan, the GPI system was similar to that in RFX-Mod, and there was a retractable Langmuir probe array at the same location as the GPI gas cloud for cross-comparison.…”

Section: E Special Features Of Various Gpi Systemsmentioning

confidence: 99%

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

Zweben

Terry

Stotler

et al. 2017

Review of Scientific Instruments

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Gas puff imaging (GPI) is a diagnostic of plasma turbulence which uses a puff of neutral gas at the plasma edge to increase the local visible light emission for improved space-time resolution of plasma fluctuations. This paper reviews gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion research, with a focus on the instrumentation, diagnostic cross-checks, and interpretation issues. The gas puff imaging hardware, optics, and detectors are described for about 10 GPI systems implemented over the past ∼15 years. Comparison of GPI results with other edge turbulence diagnostic results is described, and many common features are observed. Several issues in the interpretation of GPI measurements are discussed, and potential improvements in hardware and modeling are suggested.

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Edge turbulence scaling in RFX-mod as measured using GPI diagnostic

Cited by 16 publications

References 29 publications

Characterization of particle confinement properties in RFX-mod at a high plasma current

Characterization of particle confinement properties in RFX-mod at a high plasma current

High density physics in reversed field pinches: comparison with tokamaks and stellarators

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

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