Scrape-off-layer current loops and floating potential in limited tokamak plasmas

Loizu, Joaquim; Moralès, J.; Halpern, Federico David; Ricci, Paolo; Paruta, Paola

doi:10.1017/s0022377817000927

Cited by 12 publications

(9 citation statements)

References 26 publications

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“…The shape of this typical floating potential radial profiled has been recently explained in Ref. [26] as the result of the competition between the turbulence-driven polarization current and the poloidally asymmetric diamagnetic current, the former dominating in the near SOL. This theoretical model also predicts the progressive flattening of the V f l profiles with increasing SOL collisionality (i.e.…”

Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 67%

“…The shape of this typical floating potential radial profiled has been recently explained in Ref. [26] as the result of the competition between : Radial profiles at the OMP of parallel heat flux q || (r u ) , before N 2 injection (red) and for f rad > 70% (blue). The fit of q || (r u ) with Eq.…”

Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 74%

“…This has a two-fold motivation: first, confirming the suppression of the near SOL as it appears from IR measurements; secondly, we propose the V f l measurements as a trigger for an actuator for real time monitoring of the presence of the near SOL in a start-up phase limited plasma. Indeed, the presence of near SOL steep gradients is correlated with the presence of local nonambipolar currents flowing to the limiter [25,26]. These currents cause, in TCV limited plasmas, a drop in the floating potential radial profiles V f l (r u ) at the limiter, measured with LPs, that reach strong negative values as one approaches the LCFS.…”

Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 99%

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Impurity seeding for suppression of the near scrape-off layer heat flux feature in tokamak limited plasmas

et al. 2018

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In inboard-limited plasmas, foreseen to be used in future fusion reactors start-up and ramp down phases, the Scrape-Off Layer (SOL) exhibits two regions: the "near" and "far" SOL. The steep radial gradient of the parallel heat flux associated with the near SOL can result in excessive thermal loads onto the solid surfaces, damaging them and/or limiting the operational space of a fusion reactor. In this article, leveraging the results presented in [F. Nespoli et al., Nuclear Fusion 2017], we propose a technique for the mitigation and suppression of the near SOL heat flux feature by impurity seeding. First successful experimental results from the TCV tokamak are presented and discussed.-----------------------------------------

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Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 67%

Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 74%

Section: Experimental Setup and And Experiments Overviewmentioning

confidence: 99%

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Impurity seeding for suppression of the near scrape-off layer heat flux feature in tokamak limited plasmas

et al. 2018

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“…Rather than just using the theoretical model of MRxMHD to construct equilibria, a fully dynamical version of MRxMD based on Lagrangian variational principles has been derived [69]. SPEC has been used to study the equilibrium 𝛽-limit in classical stellarators [70]. A free-boundary capability has recently been developed [71].…”

Section: Mhd Equilibrium Toolsmentioning

confidence: 99%

Improving the stellarator through advances in plasma theory

et al. 2022

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Improvements to the stellarator concept can be realized through advancements in theoretical and computational plasma physics. Herein, recent advances are reported in the topical areas of: (1) improved energetic ion confinement, (2) the impact of three-dimensional (3D) shaping on turbulent transport, (3) reducing coil complexity, (4) novel optimization and design methods, and (5) computational magnetohydrodynamic tools. These advances enable the development of new stellarator configurations with improved confinement properties.

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“…Note that the presence of an electron current to the wall reduces the need for the wall to repel electrons, and thus large electron currents can increase the right hand side of 4.2. e electron-repelling assumption can therefore be violated at larger values of α than estimated above. Large electron currents are measured close to divertor or limiter targets in the near Scrape-O -Layer [61]. is discussion highlights the need for a kinetic electron model in future studies of the sheath and presheath.…”

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confidence: 97%

Kinetic treatment of magnetized and collisionless plasma near a wall

Geraldini¹

2018

Preprint

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Charged particles gyrate around magnetic eld lines, a property that is exploited to con ne plasma in magnetic con nement fusion devices. Typically, the gyroradius is small compared to the system size and thus the gyromotion can be averaged out. e resulting charged particle motion closely follows a magnetic eld line. At the edge of fusion devices, the magnetic eld usually impinges on a wall at a shallow angle. A boundary layer forms in which the plasma density changes over a characteristic distance from the wall of the order of the ion gyroradius, as ions are absorbed during their gyromotion.is boundary layer is called magnetic presheath, and is typically collisionless and quasineutral. Importantly, the electric eld in this region distorts the ion gyro-orbits, making them non-circular and thus a ecting the ion density pro le. Solving the magnetic presheath amounts to obtaining the self-consistent electric eld for which the net charge density is zero.In this thesis, I assume a small magnetic eld angle and small gradients parallel to the wall to develop an asymptotic theory for the magnetic presheath, which is used to obtain the ion density. e small, yet crucial, contribution of the part of the orbit near the wall is included. To demonstrate the theory for a case without any gradients parallel to the wall, I calculate numerically the self-consistent electrostatic potential by assuming the electron density to be a Boltzmann distribution. e model is used to study the dependence of magnetic presheath characteristics on magnetic eld angle and ion temperature. e distribution function of ions that have traversed the magnetic presheath is obtained, which is important to predict the amount of spu ering and erosion at the wall of a fusion device. I cannot thank enough my PhD supervisor, Felix Parra: in these four years, he has been able to simultaneously motivate, encourage and teach me in the best possible way. I also thank my co-supervisor at Culham Centre for Fusion Energy (CCFE), Fulvio Militello, for his contribution and support.Several people have given me feedback about my work. I thank Greg Hamme , Paolo Ricci, Dmitri Ryutov, Paul Dellar, Chris Ham, John Omotani and Ian Abel for discussions and comments. I am especially grateful to Paolo for reading this thesis with genuine curiosity and for giving me valuable advice.Together with Felix, Alex Schekochihin, Michael Barnes and Steve Cowley have created the perfect research environment in the Oxford Plasma eory group; I thank them for this and for their continuous feedback. Especially Alex, who not only read this thesis but has also been like a mentor.During my time in the group, I am lucky to have bridged two "generations" of students and postdocs: the "Lads on Tour" Justin, Michael F, Ferdinand and Marek; the "Plasmaniacs" Nick, Michael H, Adwiteey, Valerian, Plamen, Jason, Ollie, Mantas, Yohei and Adnane. I have enjoyed spending my days with them, as well as conferences (tours) and ping-pong games.A number of people have made my time at Oxford special. I thank all of...

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Scrape-off-layer current loops and floating potential in limited tokamak plasmas

Cited by 12 publications

References 26 publications

Impurity seeding for suppression of the near scrape-off layer heat flux feature in tokamak limited plasmas

Impurity seeding for suppression of the near scrape-off layer heat flux feature in tokamak limited plasmas

Improving the stellarator through advances in plasma theory

Kinetic treatment of magnetized and collisionless plasma near a wall

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