Nonlinear plasma sheath potential in the ASDEX Upgrade 3-strap antenna: a parameter scan

Tierens, W.; Jacquot, J.; Bobkov, V.; Noterdaeme, J.-M.; Colas, L.

doi:10.1088/1741-4326/aa7f9e

Cited by 20 publications

(28 citation statements)

References 7 publications

(21 reference statements)

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“…In references [2] and [15] typical quantitative values in the range  DC~1 0 -6  //DC in the antenna private SOL and  DC~1 0 -8  //DC in the main SOL were found to reasonably fit the measurements. Relation (12) is strictly valid only for charged particles colliding with neutrals.…”

Section: Plasma Biasing Module Of Sswichmentioning

confidence: 78%

“…Quantitative sensitivity of the simulations on loosely constrained parameters is frequently reported [20], [15], [2]. We concentrate here on relative comparisons and robust qualitative results reproducible over many runs, on several machines, in relation with experimental observations.…”

Section: Brief Panorama Of Antenna-scale Rf-sheath Modellingmentioning

confidence: 97%

“…A standalone 3D version of SSWICH-FW with metallic BCs and embedded antenna was developed as RAPLICASOL [13]. It is presently used as an antenna code in [14], [15]. An iterative solver (GM-RES) reduces the huge RAM requirements of 3D computations.…”

Section: Rf Wave Propagation Module For Tokamaksmentioning

confidence: 99%

“…Predictions were also made for WEST and ITER [30]. The project revisited the TS simulations with the upgraded SSWICH-FW tool [3], and extended the tokamak database to ASDEX upgrade (AUG) 2-strap and 3-strap antennas [14], [15] as well as JET ITER-like Antenna (ILA) [31].…”

Section: Brief Panorama Of Antenna-scale Rf-sheath Modellingmentioning

confidence: 99%

“…2D (radial/poloidal) maps of the DC plasma potential V DC were simulated on the external face of antenna side limiters (reference plane on Figure 3) for active TS antennas [2], [3], AUG 2-strap and 3-strap antennas [15], [14]. All these maps exhibit similar spatial structures.…”

Section: DC Spatial Structure Near Antenna Limitersmentioning

confidence: 99%

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SOL RF physics modelling in Europe, in support of ICRF experiments

Colas

Jacquot

et al. 2017

EPJ Web Conf.

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Abstract.A European project was undertaken to improve the available SOL ICRF physics simulation tools and confront them with measurements. This paper first reviews code upgrades within the project. Using the multi-physics finite element solver COMSOL, the SSWICH code couples RF full-wave propagation with DC plasma biasing over "antenna-scale" 2D (toroidal/radial) domains, via non-linear RF and DC sheath boundary conditions (SBCs) applied at shaped plasma-facing boundaries. For the different modules and associated SBCs, more elaborate basic research in RF-sheath physics, SOL turbulent transport and applied mathematics, generally over smaller spatial scales, guides code improvement. The available simulation tools were applied to interpret experimental observations on various tokamaks. We focus on robust qualitative results common to several devices: the spatial distribution of RF-induced DC bias; left-right asymmetries over strap power unbalance; parametric dependence and antenna electrical tuning; DC SOL biasing far from the antennas, and RF-induced density modifications. From these results we try to identify the relevant physical ingredients necessary to reproduce the measurements, e.g. accurate radiated field maps from 3D antenna codes, spatial proximity effects from wave evanescence in the near RF field, or DC current transport. Pending issues towards quantitative predictions are also outlined. ICRF antennas as active PlasmaFacing ComponentsThe phased strap arrays used to launch Ion Cyclotron Range of Frequency (ICRF, 30-80MHz) waves into magnetic fusion devices poorly radiate in vacuum: efficient coupling of the fast wave to the main plasma necessitates minimizing the distance from the straps to a critical peripheral density: the R-cutoff layer. In the Scrape-Off Layer (SOL) the antennas then behave as Plasma-facing Components (PFCs), subject to PlasmaSurface Interactions (PSI). As RF-field-emitting structures, ICRF antennas are active PFCs able to create RF-specific PSI and to modify locally their environment: enhanced ion energies, heat loads, erosion and density modifications have been observed locally. These phenomena are critical in the prospect of long-pulse machines with high-Z plasma-facing materials. Predicting the magnitude and spatial location of these processes, in relation with plasma parameters, launcher design and electrical settings, remains challenging. So far, realistic tokamak predictions relied on very simple models of oscillating double probes. A European project was undertaken to improve the available SOL RF physics simulation tools and confront them with measurements. This paper first reviews code improvements and associated basic research within the project. The available simulation tools are then applied to interpret experimental observations on various machines. From these results we exhibit qualitative properties common to the various devices, identify relevant physical ingredients necessary to reproduce the measurements, as well as pending issues towards quantitative predictions. I...

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Section: Plasma Biasing Module Of Sswichmentioning

confidence: 78%

Section: Brief Panorama Of Antenna-scale Rf-sheath Modellingmentioning

confidence: 97%

Section: Rf Wave Propagation Module For Tokamaksmentioning

confidence: 99%

Section: Brief Panorama Of Antenna-scale Rf-sheath Modellingmentioning

confidence: 99%

Section: DC Spatial Structure Near Antenna Limitersmentioning

confidence: 99%

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SOL RF physics modelling in Europe, in support of ICRF experiments

Colas

Jacquot

et al. 2017

EPJ Web Conf.

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Slab-geometry surface waves on steep gradients and the origin of related numerical issues in a variety of ICRF codes

Tierens

Colas

Team³

2021

J. Plasma Phys.

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In the ion cyclotron range of frequencies, electromagnetic surface waves are physically relevant for wave–filament interactions, parasitic edge losses and sheath–plasma waves. They are also important numerically, where non-physical surface waves may occur as side effects of slab-geometry approximations. We give new, completely general, mathematical techniques to construct dispersion relations for electromagnetic surface waves between any two media, isotropic or anisotropic, and first-order corrections for when the material interface is steep but continuous. We discuss numerical issues (localized non-convergence, undesired power generation) that arise in numerical calculations due to the presence of surface waves.

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A tutorial on radio frequency sheath physics for magnetically confined fusion devices

Myra

2021

J. Plasma Phys.

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Radio frequency (RF) sheaths occur under a wide variety of conditions when RF waves, material surfaces and plasma coexist. RF sheaths are of special importance in describing the interaction of ion cyclotron range of frequency (ICRF) waves with the boundary plasma in tokamaks, stellarators and other magnetic confinement devices. In this article the basic physics of RF sheaths is discussed in the context of magnetic fusion research. Techniques for modelling RF sheaths, their interaction with RF wave fields and the resulting consequences are highlighted. The article is intended as a guide for the early-career ICRF researcher, but it may equally well serve to provide an overview of basic RF sheath concepts and modelling directions for any interested fusion scientist.

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Nonlinear plasma sheath potential in the ASDEX Upgrade 3-strap antenna: a parameter scan

Cited by 20 publications

References 7 publications

SOL RF physics modelling in Europe, in support of ICRF experiments

SOL RF physics modelling in Europe, in support of ICRF experiments

Slab-geometry surface waves on steep gradients and the origin of related numerical issues in a variety of ICRF codes

A tutorial on radio frequency sheath physics for magnetically confined fusion devices

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