Collisionality dependent transport in TCV SOL plasmas

Garcia, Odd Erik; Pitts, R.A.; Horáček, J.; Madsen, J.; Naulin, V.; Nielsen, A. H.; Rasmussen, Jens Juul

doi:10.1088/0741-3335/49/12b/s03

Cited by 83 publications

(131 citation statements)

References 39 publications

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“…The ion temperature at the LCFS is assumed to be T T i e 0 0 = , since no ion temperature measurement was available for that discharge. Resistivity can affect substantially blobs dynamics by electrically disconnecting from the target sheaths and subsequently increasing their convective velocity, as predicted in [25] and experimentally measured in [4,27,28]. The influence of resistivity on blob dynamics has been investigated with seeded simulations in [17,29].…”

Section: Nonlinear Simulations With the Gbs Codementioning

confidence: 92%

Blob properties in full-turbulence simulations of the TCV scrape-off layer

Nespoli

Furno

Labit

et al. 2017

Plasma Phys. Control. Fusion

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To investigate blob properties in the tokamak scrape-off layer (SOL), we perform dedicated numerical nonlinear simulations of plasma turbulence in the SOL of a TCV discharge using the Global Braginskii Solver code. A blob detection technique is used for the first time in a threedimensional (3D) full-turbulence simulation to track the motion of the filaments in the SOL. The specific size, density amplitude and radial velocity of the blobs are computed, with the typical values being 7.4 s r , n 0.33 e and c 0.016 s , respectively. The analysis of blob structure in the parallel direction shows that the blobs are partially detached from the limiter. The cross correlation analysis shows how the blobs are born all along the entire field line, not being generated primarily on the low field side SOL and expanding towards the limiter. The blob radial velocity agrees well with the inertial branch of the existing scaling law. The radial particle and heat fluxes given by blobs are shown to be responsible of up to 100% and 70% of the turbulent particle and heat flux in the far SOL, respectively. The results of a second simulation with a 40 times higher resistivity are also discussed.

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Section: Nonlinear Simulations With the Gbs Codementioning

confidence: 92%

Blob properties in full-turbulence simulations of the TCV scrape-off layer

Nespoli

Furno

Labit

et al. 2017

Plasma Phys. Control. Fusion

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“…The poloidal variation of the electron temperature T e was not as dramatic as for the electron density and T e seemed to be almost independent of radius within the data scatter. LaBombard and Lipschultz clearly identified the necessity of a poloidally varying radial convection process (which is now known to be driven by the interchange instabiltiy [1][2][3][4][5]) to account for the measured density profiles. In the limiter tokamak DITE [10], the SOL T e was also found to be a weak function of the poloidal angle but, in contrast to [8], the maximum of the SOL n e was observed near the outer midplane.…”

Section: Introductionmentioning

confidence: 99%

Comparison of scrape-off layer profiles in outboard-versus inboard-limited plasmas in Tore Supra

Kočan¹,

Gunn

2010

Plasma Phys. Control. Fusion

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In the Tore Supra tokamak, the scrape-off layer profiles of discharges limited either on the inboard or on the outboard side are compared. Inboard-limited discharges are characterized by substantially longer SOL e-folding lengths of ion and electron temperatures and electron density measured near the top of the plasma, providing strong evidence that the ion and electron energy transport across the SOL is enhanced on the outboard side, similar to the particle transport. The parallel heat flux density extrapolated to the last closed flux surface is found to be inversely proportional to its e-folding length in the SOL. The outboard limiters thus receive higher and more peaked heat loads than the inboard limiters. These results are important for the optimization of the plasma start-up scenario and design of the first wall in ITER.PACS 52.25.Fi, 52.25.Xz, 52.35.Ra, 52.55.Fa, 52.70.Ds IntroductionIn tokamaks, the intermittent expulsion of magnetic-field-aligned plasma filaments from the last closed flux surface (LCFS) is responsible for a large fraction of the effective radial transport to the wall [1][2][3][4][5][6]. Filament propagation appears to be governed by a ballooning-type instability in the unfavourable magnetic curvature region on the low field side. As the filaments propagate outward, they also expand freely along the magnetic field lines, driving pressure-driven field-direction-independent parallel flows. Mach probe measurements in many divertor tokamaks (e.g. [7] and references therein) show flow patterns consistent with this model (i.e. stagnant flow poloidally approximately halfway between the outer midplane and the X-point), in which the filaments can be seen as an important particle source in the scrape-off layer (SOL). Similar observations in limiter tokamaks [8][9][10][11][12] prove that enhanced radial particle transport on the outboard side of the plasma is a universal phenomenon, independent of the presence of an X-point divertor. The enhancement of the radial particle transport on the outboard side of the limiter plasmas was confirmed by the 3D fluid turbulence code TOKAM-3D [13]. When the plasma contact point is on the inboard limiters, the filaments propagate freely out to the wall, filling all the available volume outside the LCFS and leading to a broad SOL with nearly flat density profiles. On the other hand, it was demonstrated [12] that outboard modular limiters suppress the radial particle transport when they are near the LCFS, leading to a very thin SOL. It is probable [8] that the limiters act as simple mechanical barriers that intercept the parallel particle flux in the region in which the enhanced radial convection.

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“…[11][12][13][14][15] The turbulence-driven transport results in broad plasma profiles in the SOL and enhanced levels of plasma--wall interactions that may be an issue for the next generation plasma confinement experiments and future fusion power reactors. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] The radial motion of blob-like structures leads to largeamplitude bursts in single-point measurements. The statistical properties of these bursts in the SOL of several tokamak plasmas have recently been elucidated by the analysis of long data time series from probe measurements and gas puff imaging.…”

Section: Introductionmentioning

confidence: 99%

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

et al. 2016

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A stochastic model is presented for intermittent fluctuations in the scrape-off layer of magnetically confined plasmas. The fluctuations in the plasma density are modeled by a super-position of uncorrelated pulses with fixed shape and duration, describing radial motion of blob-like structures. In the case of an exponential pulse shape and exponentially distributed pulse amplitudes, predictions are given for the lowest order moments, probability density function, auto-correlation function, level crossings, and average times for periods spent above and below a given threshold level. Also, the mean squared errors on estimators of sample mean and variance for realizations of the process by finite time series are obtained. These results are discussed in the context of single-point measurements of fluctuations in the scrape-off layer, broad density profiles, and implications for plasma--wall interactions due to the transient transport events in fusion grade plasmas. The results may also have wide applications for modelling fluctuations in other magnetized plasmas such as basic laboratory experiments and ionospheric irregularities. Published by AIP Publishing.

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Collisionality dependent transport in TCV SOL plasmas

Cited by 83 publications

References 39 publications

Blob properties in full-turbulence simulations of the TCV scrape-off layer

Blob properties in full-turbulence simulations of the TCV scrape-off layer

Comparison of scrape-off layer profiles in outboard-versus inboard-limited plasmas in Tore Supra

Stochastic modelling of intermittent fluctuations in the scrape-off layer: Correlations, distributions, level crossings, and moment estimation

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