Understanding core heavy impurity transport in a hybrid discharge on EAST

2021 ◽  
Author(s):  
Shengyu Shi ◽  
Jiale Chen ◽  
Clarisse Bourdelle ◽  
Xiang Jian ◽  
Tomas Odstrcil ◽  
...  
Keyword(s):  
Density Profile ◽  
Central Region ◽  
Turbulent Transport ◽  
Accumulation Process ◽  
Plasma Parameters ◽  
Toroidal Rotation ◽  
The Core ◽  
Impurity Transport ◽  
Accumulation Phase ◽  
Bulk Plasma

Abstract The behavior of heavy/high-Z impurity tungsten (W) in the core of hybrid (high normalized beta β_N plasmas) scenario on EAST with ITER-like divertor (ILD) is analyzed. W accumulation is often observed and seriously degrades the plasma performance (Xiang Gao et al 2017 Nucl. Fusion 57 056021). The dynamics of the W accumulation process of a hybrid discharge are examined considering the concurrent evolution of the background plasma parameters. It turns out that the toroidal rotation and density peaking of the bulk plasma are usually large in the central region, which is particularly prone to the W accumulation. A time slice during the W accumulation phase is modeled, accounting for both neoclassical and turbulent transport components of W, through NEO with poloidal asymmetry effects induced by toroidal rotation, and TGLF, respectively. This modeling reproduces the experimental observations of W accumulation and identifies the neoclassical inward convection/pinch velocity of W due to the large density peaking of the bulk plasma and toroidal rotation in the central region as one of the main reasons for the W accumulation. In addition, the NEO+TGLF+STRAHL modeling can not only predict the core W density profile but also closely reconstruct the radiated information mainly produced by W in the experiment.

Understanding core tungsten (W) transport and control in an improved high-performance fully non-inductive discharge on EAST

2021 ◽  
Author(s):  
Shengyu Shi ◽  
Jiale Chen ◽  
Clarisse Bourdelle ◽  
Xiang Jian ◽  
Tomas Odstrcil ◽  
...  
Keyword(s):  
Density Profile ◽  
Turbulent Diffusion ◽  
High Performance ◽  
Electron Cyclotron Resonance ◽  
Transport Coefficients ◽  
Linear Instability ◽  
Electron Cyclotron Resonance Heating ◽  
Plasma Parameters ◽  
Turbulent Diffusion Coefficient ◽  
Inductive Discharge

Abstract The behavior of heavy/high-Z impurity tungsten (W) in an improved high-performance fully non-inductive discharge on EAST with ITER-like divertor (ILD) is analyzed. It is found that W could be well controlled. The causes of no W accumulation are clarified by analyzing the background plasma parameters and modeling the W transport. It turns out that the electron temperature (T_e) and its gradient are usually high while the toroidal rotation and density peaking of the bulk plasma are small. In this condition, the modeled W turbulent diffusion coefficient is big enough to offset the total turbulent and neoclassical pinch, so that W density profile for zero particle flux will not be very peaked. Combining NEO and TGLF for the W transport coefficient and the impurity transport code STRAHL, not only the core W density profile is predicted but also the radiated information mainly produced by W in the experiment can be closely reconstructed. At last, the physics of controlling W accumulation by electron cyclotron resonance heating (ECRH) is illustrated considering the effects of changed T_e by ECRH on ionization balance and transport of W. It shows that the change of ionization and recombination balance by changed T_e is not enough to explain the experimental observation of W behavior, which should be attributed to the changed W transport. By comparing the W transport coefficients in two kinds of plasmas with different T_e profiles, it is shown that high T_e and its gradient play a key role to generate large turbulent diffusion through increasing the growth rate of linear instability so that W accumulation is prevented.

scholarly journals COMPARISON BETWEEN 2D TURBULENCE MODEL ESEL AND EXPERIMENTAL DATA FROM AUG AND COMPASS TOKAMAKS

2015 ◽  
Vol 55 (2) ◽  
pp. 128-135 ◽  
Author(s):  
Peter Ondac ◽  
Jan Horacek ◽  
Jakub Seidl ◽  
Petr Vondrácek ◽  
Hans Werner Müller ◽  
...  
Keyword(s):  
Turbulent Transport ◽  
Plasma Potential ◽  
Density Fluctuations ◽  
Tokamak Plasma ◽  
Plasma Parameters ◽  
Fluid Turbulence ◽  
Radial Profiles ◽  
Parallel Dynamics ◽  
Two Machines ◽  
Probe Measurements

<!-- p, li { white-space: pre-wrap; } --><p style="text-indent: 0px; margin: 0px;">In this article we have used the 2D fluid turbulence numerical model, ESEL, to simulate turbulent transport in edge tokamak plasma. Basic plasma parameters from the ASDEX Upgrade and COMPASS tokamaks are used as input for the model, and the output is compared with experimental observations obtained by reciprocating probe measurements from the two machines. Agreements were found in radial profiles of mean plasma potential and temperature, and in a level of density fluctuations. Disagreements, however, were found in the level of plasma potential and temperature fluctuations. This implicates a need for an extension of the ESEL model from 2D to 3D to fully resolve the parallel dynamics, and the coupling from the plasma to the sheath.</p>

Neoclassical impurity transport in the core of an ignited tokamak plasma

2000 ◽  
Vol 40 (10) ◽  
pp. 1721-1729 ◽  
Author(s):  
R Dux ◽  
A.G Peeters
Keyword(s):  
Tokamak Plasma ◽  
The Core ◽  
Impurity Transport

Evolution of atmospheric aerosol particles during a pollution accumulation process: a case study

2015 ◽  
Vol 12 (1) ◽  
pp. 51-60 ◽  
Author(s):  
Hongya Niu ◽  
Wei Hu ◽  
Wei Pian ◽  
Jingsen Fan ◽  
Jinxi Wang
Keyword(s):  
Fine Particles ◽  
Aerosol Particles ◽  
Urban Site ◽  
Accumulation Process ◽  
Soot Particles ◽  
Secondary Particles ◽  
The Core ◽  
Pollution Accumulation ◽  
Number Frequency ◽  
Haze Formation

The characteristics of fine aerosol particles were investigated at an urban site in Beijing during an atmospheric pollution accumulation process. The organics, sulfate and BC were the dominant components in fine particles in the clear air, and the concentrations of organics, sulfate, nitrate and ammonium increased during the haze formation. The mass concentrations of primary species (chloride and BC) in the clear air were similar to those in the haze. The morphology, mixing state and aging status of fine particles in the clear air were different from those in the haze. Accumulation secondary particles were detected with high frequency and accumulation secondary particles with coating were rare in all the samples. The frequency of soot particles with coating in the clear air was lower than that in the haze. The number ratio of accumulation secondary particles to soot containing particles changed from 3:1 in clear air to 2:3 in the haze. These results indicated that the number frequency of accumulation secondary particles decreased while that of the soot containing particles increased with the air pollutants accumulating. The core-shell ratio of coated soot particles ranged between 0.1–0.6 was 62% in the clear air, and 82% in the haze. The mode sizes for the core and the shell of soot particles were 0.35 μm and 0.55 μm in the clear air, and 0.35 μm and 1.0 μm in the haze, respectively. The mean diameters of the core and the shell were 0.3 μm and was 0.6 μm in the clear air, and 0.4 μm and 1.0 μm in the haze, respectively. These results indicated that with the air pollution accumulating, the frequency of accumulation secondary particles decreased while the soot containing particles increased. The aging process of soot particles was stronger in the haze, and resulted in greater hygroscopicity for soot particles in the haze.

scholarly journals Techniques for measuring high-resolution firn density profiles: case study from Kongsvegen, Svalbard

2008 ◽  
Vol 54 (186) ◽  
pp. 463-468 ◽  
Author(s):  
Robert L. Hawley ◽  
Ola Brandt ◽  
Elizabeth M. Morris ◽  
Jack Kohler ◽  
Andrew P. Shepherd ◽  
...  
Keyword(s):  
High Resolution ◽  
Electrical Properties ◽  
Density Profile ◽  
Large Scale ◽  
Ice Core ◽  
Fine Scale ◽  
Density Profiles ◽  
The Core ◽  
Core Section

AbstractOn an 11 m firn/ice core from Kongsvegen, Svalbard, we have used dielectric profiling (DEP) to measure electrical properties, and digital photography to measure a core optical stratigraphy (COS) profile. We also used a neutron-scattering probe (NP) to measure a density profile in the borehole from which the core was extracted. The NP- and DEP-derived density profiles were similar, showing large-scale (>30 cm) variation in the gravimetric densities of each core section. Fine-scale features (<10 cm) are well characterized by the COS record and are seen at a slightly lower resolution in both the DEP and NP records, which show increasing smoothing. A combination of the density accuracy of NP and the spatial resolution of COS provides a useful method of evaluating the shallow-density profile of a glacier, improving paleoclimate interpretation, mass-balance measurement and interpretation of radar returns.

Zdependence of the core impurity transport in ASDEX Upgrade H mode discharges

1999 ◽  
Vol 39 (11) ◽  
pp. 1509-1522 ◽  
Author(s):  
R Dux ◽  
A.G Peeters ◽  
A Gude ◽  
A Kallenbach ◽  
R Neu ◽  
...  
Keyword(s):  
The Core ◽  
Impurity Transport

scholarly journals Impurity temperature screening in stellarators close to quasisymmetry

2020 ◽  
Vol 86 (3) ◽  
Author(s):  
Mike F. Martin ◽  
Matt Landreman
Keyword(s):  
Magnetic Field ◽  
Kinetic Equation ◽  
Particle Flux ◽  
Radial Electric Field ◽  
Impurity Particle ◽  
The Core ◽  
Impurity Transport ◽  
Radial Flux ◽  
Impurity Ions ◽  
The Magnetic Field

Impurity temperature screening is a favourable neoclassical phenomenon involving an outward radial flux of impurity ions from the core of fusion devices. Quasisymmetric magnetic fields lead to intrinsically ambipolar neoclassical fluxes that give rise to temperature screening for low enough $\unicode[STIX]{x1D702}^{-1}\equiv d\ln n/d\ln T$ . In contrast, neoclassical fluxes in generic stellarators will depend on the radial electric field, which is predicted to be inward for ion-root plasmas, potentially leading to impurity accumulation. Here, we examine the impurity particle flux in a number of approximately quasisymmetric stellarator configurations and parameter regimes while varying the amount of symmetry breaking in the magnetic field. For the majority of this work, neoclassical fluxes have been obtained using the SFINCS drift-kinetic equation solver with electrostatic potential $\unicode[STIX]{x1D6F7}=\unicode[STIX]{x1D6F7}(r)$ , where $r$ is a flux-surface label. Results indicate that achieving temperature screening is possible, but unlikely, at low-collisionality reactor-relevant conditions in the core. Thus, the small departures from symmetry in nominally quasisymmetric stellarators are large enough to significantly alter the neoclassical impurity transport. A further look at the magnitude of these fluxes when compared to a gyro-Bohm turbulence estimate suggests that neoclassical fluxes are small in configurations optimized for quasisymmetry when compared to turbulent fluxes.

Formation of impurity transport barrier in LHD plasmas with hollow density profile

2017 ◽  
Vol 57 (8) ◽  
pp. 086031 ◽  
Author(s):  
X.L. Huang ◽  
S. Morita ◽  
T. Oishi ◽  
I. Murakami ◽  
M. Goto ◽  
...  
Keyword(s):  
Density Profile ◽  
Transport Barrier ◽  
Impurity Transport

Turbulent Transport Measurements in a Heated Boundary Layer: Combined Effects of Free-Stream Turbulence and Removal of Concave Curvature

1997 ◽  
Vol 119 (3) ◽  
pp. 413-419 ◽  
Author(s):  
M. D. Kestoras ◽  
T. W. Simon
Keyword(s):  
Boundary Layer ◽  
Free Stream ◽  
Turbulent Transport ◽  
Outer Part ◽  
Test Facility ◽  
Free Stream Turbulence ◽  
The Core ◽  
Concave Wall ◽  
Prandtl Numbers ◽  
Near Wall

Turbulence measurements for both momentum and heat transport are taken in a boundary layer over a flat recovery wall downstream of a concave wall (R = 0.97 m). The boundary layer appears turbulent from the beginning of the upstream, concave wall and grows over the flat test wall downstream of the curved wall with negligible streamwise acceleration. The strength of curvature at the bend exit, δ99.5/R, is 0.04. The free-stream turbulence intensity (FSTI) is ~8 percent at the beginning of the curve and is nearly uniform at ~4.5 percent throughout the recovery wall. Comparisons are made with data taken in an earlier study, in the same test facility, but with a low FSTI (~0.6 percent). Results show that on the recovery wall, elevated FSTI enhances turbulent transport quantities such as −uν and νt in most of the outer part of the boundary layer, but near-wall values of νt remain unaffected. This is in contrast to near-wall νt values within the curve which decrease when FSTI is increased. At the bend exit, decreases of −uν and νt due to removal of curvature become more profound when FSTI is elevated, compared to low-FSTI behavior. Measurements in the core of the flow indicate that the high levels of cross transport of momentum over the upstream concave wall cease when curvature is removed. Other results show that turbulent Prandtl numbers over the recovery wall are reduced to ~0.9 when FSTI is elevated, consistent with the rise in Stanton numbers over the recovery wall.

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