Mechanism for blob generation in the TORPEX toroidal plasma

Furno, I.; Labit, B.; Fasoli, A.; Poli, F. M.; Ricci, Paolo; Theiler, C.; Brunner, S.; Diallo, A.; Graves, J. P.; Podestà, M.; Müller, Stefan

doi:10.1063/1.2870082

Cited by 68 publications

(84 citation statements)

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“…With the present plasma parameters, the relevant collision frequencies of the suprathermal Li6 + ions with background thermal ions are ν s,i ≈ 16 s −1 and with neutrals ν s,n ≈ 6.2 × 10 3 s −1 , respectively. As these frequencies are typically much smaller than the gyrofrequency ≈ 188 × 10 3 s −1 for Li6 + ions in TORPEX and the ideal interchange growth rate is ≈ 8 × 10 4 s −1 (Furno et al 2008a), the suprathermal ions are magnetized. For reference, the respective collision frequencies for the thermal ions are ν i,i ≈ 7 × 10 3 s −1 and with neutrals ν i,n ≈ 5 × 10 4 s −1 .…”

Section: Suprathermal Ion Physicsmentioning

confidence: 99%

“…The particle fluxes associated with the creation of the quasi-equilibrium are compared with those related to fluctuating density and potential, both locally and in conjunction with macroscopic fluctuating structures. To this aim, a modified conditional sampling technique has been developed which allows simultaneous measurements of time-resolved, two dimensional profiles of electron density, and temperature and plasma potential (Furno et al 2008a). These measurements are complemented by direct observation of turbulent structures and related particle flux as obtained by a spatio-temporal pattern recognition method, which was previously developed on the TORPEX device ).…”

Section: Major Research Questionsmentioning

confidence: 99%

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Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

et al. 2015

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The TORPEX basic plasma physics device at the Center for Plasma Physics Research (CRPP) in Lausanne, Switzerland is described. In TORPEX, simple magnetized toroidal configurations, a paradigm for the tokamak scrape-off layer (SOL), as well as more complex magnetic geometries of direct relevance for fusion are produced. Plasmas of different gases are created and sustained by microwaves in the electron-cyclotron (EC) frequency range. Full diagnostic access allows for a complete characterization of plasma fluctuations and wave fields throughout the entire plasma volume, opening new avenues to validate numerical codes. We detail recent advances in the understanding of basic aspects of plasma turbulence, including its development from linearly unstable electrostatic modes, the formation of filamentary structures, or blobs, and its influence on the transport of energy, plasma bulk and suprathermal ions. We present a methodology for the validation of plasma turbulence codes, which focuses on quantitative assessment of the agreement between numerical simulations and TORPEX experimental data.

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Section: Suprathermal Ion Physicsmentioning

confidence: 99%

Section: Major Research Questionsmentioning

confidence: 99%

Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

et al. 2015

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“…More details on similar scenarios, including the mechanisms for blob generation and the statistical properties of the fluctuations, are given in Refs. [12,14,20].…”

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confidence: 99%

“…The effects of finite T e fluctuations, independently measured with a triple probe, are included. The two-dimensional ÿ and Q are calculated from the time series of n, T e and reconstructed from conditionally sampled (CS) data from swept Langmuir probes [15,20,21]. The spatial resolution of the reconstructed CS signals is 1 cm radially and 1.8 cm vertically.…”

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confidence: 99%

Cross-Field Transport by Instabilities and Blobs in a Magnetized Toroidal Plasma

et al. 2008

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The mechanisms for anomalous transport across the magnetic field are investigated in a toroidal magnetized plasma. The role of plasma instabilities and macroscopic density structures (blobs) is discussed. Examples from a scenario with open magnetic field lines are shown. A transition from a main plasma region into a loss region is reproduced. In the main plasma, which includes particle and heat source locations, the transport is dominated by the fluctuation-induced particle and heat flux associated with a plasma instability. On the low-field side, the cross-field transport is ascribed to the intermittent ejection of macroscopic blobs propagating toward the outer wall. It is shown that instabilities and blobs represent fundamentally different mechanisms for cross-field transport. It is widely recognized that the transport of particles and heat across the magnetic field in magnetically confined plasmas is anomalous, i.e., much larger than the transport induced by collisional processes [1]. Similar statistical properties, observed in different physical systems and/or for a variety of experimental conditions [2], suggest that the mechanisms responsible for the anomalous cross-field transport may have a common fundamental character. In particular, the possible relationship with low-frequency electrostatic instabilities has been suggested [3]. Correlated fluctuations of density and potential associated with unstable modes can directly drive a cross-field flux [4]. In addition, losses are partly due to the ejection of blobs, i.e., macroscopic density perturbations stretched along the magnetic field [5]. Theoretical [6 -8] and experimental [9,10] investigations are shedding light upon the mechanisms governing the blob dynamics, hence the associated transport [1,11]. However, despite the fundamental difference in the properties of instabilities and blobs, no clear distinction is usually done between their contributions to the total transport, generically interpreted in terms of a turbulent flux.In this Letter, we address the question of the different contributions to the cross-field transport in a simple magnetized toroidal plasma from instabilities and blobs. It is shown that the associated mechanisms for cross-field transport present fundamental differences. Therefore, the corresponding transport rates should be measured through complementary techniques to fully characterize the turbulent flux. For the scenario investigated herein, a main plasma and an edge region, connected by a transition region, can be clearly separated [12]. An interchange instability develops in the main plasma [13]. Blobs originate from the instability in the transition region, then propagate toward the outer wall across the magnetic field [12,14]. Although * 90% of the total losses on TORPEX plasmas are due to losses along the open magnetic field lines [15], in this Letter we focus on cross-field transport induced by perturbations of the plasma parameters.In general, the instantaneous particle flux is nv, where n is the local plasma density and...

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“…Here, a scenario with B t = 74 mT and B v = 2 mT is used, resulting in a SMT with vertical magnetic field line return distance D ≈ 17 cm, which is dominated by an ideal interchange mode with wavenumbers k ≈ 0, and, k ⊥ ≈ 37 m −1 . This scenario, similar to those extensively studied in Furno et al (2008aFurno et al ( , 2008b, Müller et al (2007), Theiler et al (2008), , Podestà et al (2008), Labit et al (2011), Furno et al (2011 using electrostatic probes, is characterized by the presence of a region on the lowfield side where coherent structures are observed to propagate radially outward resulting in intermittent non-Gaussian transport of particles, heat, momentum and current.…”

Section: Non-diffusive Transport Arising From the Combination Of Smalmentioning

confidence: 98%

Nonclassical Transport and Particle-Field Coupling: from Laboratory Plasmas to the Solar Wind

Perrone

Dendy

Furno

et al. 2013

Space Sciences Series of ISSI

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Understanding transport of thermal and suprathermal particles is a fundamental issue in laboratory, solar-terrestrial, and astrophysical plasmas. For laboratory fusion experiments, confinement of particles and energy is essential for sustaining the plasma long enough to reach burning conditions. For solar wind and magnetospheric plasmas, transport properties determine the spatial and temporal distribution of energetic particles, which can be harmful for spacecraft functioning, as well as the entry of solar wind plasma into the magnetosphere. For astrophysical plasmas, transport properties determine the efficiency of particle acceleration processes and affect observable radiative signatures. In all cases, transport depends on the interaction of thermal and suprathermal particles with the electric and magnetic fluctuations in the plasma. Understanding transport therefore requires us to understand these interactions, which encompass a wide range of scales, from magnetohydrodynamic to kinetic scales, with larger scale structures also having a role. The wealth of transport studies during recent decades has shown the existence of a variety of regimes that differ from the classical quasilinear regime. In this paper we give an overview of nonclassical plasma transport regimes, discussing theoretical approaches to superdiffusive and subdiffusive transport, wave-particle interactions at microscopic kinetic scales, the influence of coherent structures and of avalanching transport, and the results of numerical simulations and experimental data analyses. Applications to laboratory plasmas and space plasmas are discussed.

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Mechanism for blob generation in the TORPEX toroidal plasma

Cited by 68 publications

References 34 publications

Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

Plasma turbulence, suprathermal ion dynamics and code validation on the basic plasma physics device TORPEX

Cross-Field Transport by Instabilities and Blobs in a Magnetized Toroidal Plasma

Nonclassical Transport and Particle-Field Coupling: from Laboratory Plasmas to the Solar Wind

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