Fluid, kinetic and hybrid approaches for neutral and trace ion edge transport modelling in fusion devices

2021 ◽  
Author(s):  
Dmitriy V. Borodin ◽  
Friedrich Schluck ◽  
Sven Wiesen ◽  
D M Harting ◽  
Petra Boerner ◽  
...  
Keyword(s):  
Fluid Model ◽  
Plasma Chemistry ◽  
Molecular Ions ◽  
Edge Plasma ◽  
Hybrid Technique ◽  
Transport Modelling ◽  
Hybrid Approaches ◽  
Neutral Gas ◽  
Order Of Magnitude ◽  
Key Aspects

Abstract Neutral gas physics and neutral interactions with the plasma are key aspects of edge plasma and divertor physics in a fusion reactor including the detachment phenomenon often seen as key to dealing with the power exhaust challenges. A full physics description of the neutral gas dynamics requires a 6D kinetic approach, potentially time dependent, where the details of the wall geometry play a substantial role, to the extent that, e.g., the subdivertor region has to be included. The Monte Carlo (MC) approach used for about 30 years in EIRENE [1], is well suited to solve these types of complex problems. Indeed, the MC approach allows simulating the 6D kinetic equation without having to store the velocity distribution on a 6D grid, at the cost of introducing statistical noise. MC also provides very good flexibility in terms of geometry and atomic and molecular (A&M) processes. However, it becomes computationally extremely demanding in high-collisional regions (HCR) as anticipated in ITER and DEMO. Parallelization on particles helps reducing the simulation wall clock time, but to provide speed-up in situations where single trajectories potentially involve a very large number of A&M events, it is important to derive a hierarchy of models in terms of accuracy and to clearly identify for what type of physics issues they provide reliable answers. It was demonstrated that advanced fluid neutral (AFN) models are very accurate in HCRs, and at least an order of magnitude faster than fully kinetic simulations. Based on these fluid models, three hybrid fluid-kinetic approaches are introduced: a spatially hybrid technique (SpH), a micro-Macro hybrid method (mMH), and an asymptotic-preserving MC (APMC) scheme, to combine the efficiency of a fluid model with the accuracy of a kinetic description. In addition, atomic and molecular ions involved in the edge plasma chemistry can also be treated kinetically within the MC solver, opening the way for further hybridisation by enabling kinetic impurity ion transport calculations. This paper aims to give an overview of methods mentioned and suggests the most prospective combinations to be developed.

scholarly journals A numerical model of the ionosphere, including the E-region above EISCAT

1996 ◽  
Vol 14 (2) ◽  
pp. 191-200 ◽  
Author(s):  
P.-Y. Diloy ◽  
A. Robineau ◽  
J. Lilensten ◽  
P.-L. Blelly ◽  
J. Fontanari
Keyword(s):  
Electric Field ◽  
Fluid Model ◽  
Molecular Ions ◽  
Ion Concentration ◽  
Topside Ionosphere ◽  
Ion Chemistry ◽  
Vhf Radar ◽  
Theoretical Predictions ◽  
Consistent Manner ◽  
E Region

Abstract. It has been previously demonstrated that a two-ion (O+ and H+) 8-moment time-dependent fluid model was able to reproduce correctly the ionospheric structure in the altitude range probed by the EISCAT-VHF radar. In the present study, the model is extended down to the E-region where molecular ion chemistry (NO+ and O+2, essentially) prevails over transport; EISCAT-UHF observations confirmed previous theoretical predictions that during events of intense E×B induced convection drifts, molecular ions (mainly NO+) predominate over O+ ions up to altitudes of 300 km. In addition to this extension of the model down to the E-region, the ionization and heating resulting from both solar insolation and particle precipitation is now taken into account in a consistent manner through a complete kinetic transport code. The effects of E×B induced convection drifts on the E- and F-region are presented: the balance between O+ and NO+ ions is drastically affected; the electric field acts to deplete the O+ ion concentration. The [NO+]/[O+] transition altitude varies from 190 km to 320 km as the perpendicular electric field increases from 0 to 100 mV m-1. An interesting additional by-product of the model is that it also predicts the presence of a noticeable fraction of N+ ions in the topside ionosphere in good agreement with Retarding Ion Mass Spectrometer measurements onboard Dynamic Explorer.

scholarly journals Dissipation of turbulence by magnetohydrodynamic shock waves

2015 ◽  
Vol 11 (S315) ◽  
Author(s):  
Andrew Lehmann ◽  
Mark Wardle
Keyword(s):  
Shock Front ◽  
Fluid Model ◽  
Neutral Species ◽  
One Dimensional ◽  
Neutral Gas ◽  
Gas Dynamic ◽  
Magnetohydrodynamic Shock ◽  
Two Fluid Model ◽  
Ion Species ◽  
Two Fluid

AbstractWe characterise steady, one-dimensional fast and slow magnetohydrodynamic (MHD) shocks using a two-fluid model. Fast MHD shocks are magnetically driven, forcing ions to stream through the neutral gas ahead of the shock front. This magnetic precursor heats the gas sufficiently to create a large, warm transition zone where all fluid variables only weakly change in the shock front. In contrast, slow MHD shocks are driven by gas pressure where neutral species collide with ion species in a thin hot slab that closely resembles an ordinary gas dynamic shock.We computed observational diagnostics for fast and slow shocks at velocities vs=2–4 km/s and preshock Hydrogen nuclei densities nH = 102-4 cm−3. We followed the abundances of molecules relevant for a simple oxygen chemistry and include cooling by CO, H2 and H2O. Estimates of intensities of 12CO rotational lines show that high-J lines, above J = 6 → 5, are more strongly excited in slow MHD shocks.

scholarly journals The ACCELERATION programme: I. Cosmology with the redshift drift

2019 ◽  
Vol 492 (2) ◽  
pp. 2044-2057
Author(s):  
Ryan Cooke
Keyword(s):  
Local Density ◽  
Current Data ◽  
Cosmological Redshift ◽  
Star Forming ◽  
Star Forming Regions ◽  
Neutral Gas ◽  
Small Correction ◽  
Redshift Drift ◽  
Universal Expansion ◽  
Order Of Magnitude

ABSTRACT Detecting the change of a cosmological object’s redshift due to the time evolution of the Universal expansion rate is an ambitious experiment that will be attempted with future telescope facilities. In this paper, we describe the ACCELERATION programme, which aims to study the properties of the most underdense regions of the Universe. One of the highlight goals of this programme is to prepare for the redshift drift measurement. Using the EAGLE cosmological hydrodynamic simulations, we estimate the peculiar acceleration of gas in galaxies and the Lyα forest. We find that star-forming ‘cold neutral gas’ exhibits large peculiar acceleration due to the high local density of baryons near star-forming regions. We conclude that absorption by cold neutral gas is unlikely to yield a detection of the cosmological redshift drift. On the other hand, we find that the peculiar accelerations of Lyα forest absorbers are more than an order of magnitude below the expected cosmological signal. We also highlight that the numerous low H i column density systems display lower peculiar acceleration. Finally, we propose a new ‘Lyα cell’ technique that applies a small correction to the wavelength calibration to secure a relative measurement of the cosmic drift between two unrelated cosmological sources at different redshifts. For suitable combinations of absorption lines, the cosmological signal can be more than doubled, while the affect of the observer peculiar acceleration is mitigated. Using current data of four suitable Lyα cells, we infer a limit on the cosmological redshift drift to be $\dot{v}_{\rm obs}\lt 65~{\rm m~s}^{-1}~{\rm yr}^{-1}$ (2σ).

Improving parallel scalability for edge plasma transport simulations with neutral gas species

2012 ◽  
Vol 5 (1) ◽  
pp. 014012 ◽  
Author(s):  
M McCourt ◽  
T D Rognlien ◽  
L C McInnes ◽  
H Zhang
Keyword(s):  
Edge Plasma ◽  
Plasma Transport ◽  
Parallel Scalability ◽  
Neutral Gas

Lagrangian accelerations of particles in superfluid turbulence

2013 ◽  
Vol 717 ◽  
Author(s):  
M. La Mantia ◽  
D. Duda ◽  
M. Rotter ◽  
L. Skrbek
Keyword(s):  
Quantum Turbulence ◽  
Fluid Model ◽  
Quantized Vortices ◽  
Superfluid Turbulence ◽  
Thermal Counterflow ◽  
Length Scales ◽  
Order Of Magnitude ◽  
The Mean ◽  
Two Fluid Model ◽  
Two Fluid

AbstractQuantum turbulence in thermal counterflow of superfluid ${\text{} }^{4} \mathrm{He} $ is studied at length scales comparable to the mean distance $\ell $ between quantized vortices. The Lagrangian dynamics of solid deuterium particles, of radius ${R}_{p} $ about one order of magnitude smaller than $\ell $, is analysed in a planar section of the experimental volume by using the particle tracking velocimetry technique. We show that the average amplitude of the acceleration of the particles seems to increase as the temperature decreases and applied heat flux increases and this can be explained by exploiting the two-fluid model of superfluid ${\text{} }^{4} \mathrm{He} $. We also report that, at the probed length scales, the normalized distribution of the acceleration of the particles appears to follow an unexpected classical-like behaviour.

scholarly journals Minimally Invasive Treatment of the Thoracic Spine Disease: Completely Percutaneous and Hybrid Approaches

2013 ◽  
Vol 2013 ◽  
pp. 1-6
Author(s):  
Tamburrelli Francesco Ciro ◽  
Scaramuzzo Laura ◽  
Genitiempo Maurizio ◽  
Proietti Luca
Keyword(s):  
Minimally Invasive ◽  
Thoracic Spine ◽  
Postoperative Recovery ◽  
Hybrid Technique ◽  
Open Approach ◽  
Invasive Treatment ◽  
Invasive Approach ◽  
Percutaneous Approach ◽  
Hybrid Approaches ◽  
Spine Disease

The aim of the study was to evaluate the feasibility of a limited invasive approach for the treatment of upper thoracic spine disease. Seven patients with type-A thoracic fractures and three with tumors underwent long thoracic stabilization through a minimally invasive approach. Four patients underwent a completely percutaneous approach while the other three underwent a modified hybrid technique, a combination of percutaneous and open approach. The hybrid constructs were realized using a percutaneous approach to the spine distally to the spinal lesion and by open approach proximally. In two patients, the stabilization was extended proximally up to the cervical spine. Clinical and radiographic assessment was performed during the first year after the operation at 3, 6, and 12 months. No technically related complications were seen. The postoperative recovery was rapid even in the tumor patients with neurologic impairment. Blood loss was irrelevant. At one-year follow-up there was no loosening or breakage of the screws or failure of the implants. When technically feasible a completely percutaneous approach has to be taken in consideration; otherwise, a combined open-percutaneous approach could be planned to minimize the invasivity of a completely open approach to the thoracic spine.

A Dynamic hp-Adaptive Discontinuous Galerkin Method for Shallow-Water Flows on the Sphere with Application to a Global Tsunami Simulation

2012 ◽  
Vol 140 (3) ◽  
pp. 978-996 ◽  
Author(s):  
Sébastien Blaise ◽  
Amik St-Cyr
Keyword(s):  
Shallow Water ◽  
Discontinuous Galerkin ◽  
Three Dimensional ◽  
Computational Time ◽  
Error Estimator ◽  
Tsunami Propagation ◽  
Tsunami Simulation ◽  
Shallow Water Flows ◽  
Order Of Magnitude ◽  
Key Aspects

Abstract A discontinuous Galerkin model solving the shallow-water equations on the sphere is presented. It captures the dynamically varying key aspects of the flows by having the advantageous ability to locally modify the mesh as well as the order of interpolation within each element. The computational load is efficiently distributed among processors in parallel using a weighted recursive coordinate bisection strategy. A simple error estimator, based on the discontinuity of the variables at the interfaces between elements, is used to select the elements to be refined or coarsened. The flows are expressed in three-dimensional Cartesian coordinates, but tangentially constrained to the sphere by adding a Lagrange multiplier to the system of equations. The model is validated on classic atmospheric test cases and on the simulation of the February 2010 Chilean tsunami propagation. The proposed multiscale strategy is able to reduce the computational time by an order of magnitude on the tsunami simulation, clearly demonstrating its potential toward multiresolution three-dimensional oceanic and atmospheric applications.

Appearance Potentials of Metastable Molecular Ions

1967 ◽  
Vol 22 (1) ◽  
pp. 40-47 ◽  
Author(s):  
I. Hertel ◽  
Ch. Ottinger
Keyword(s):  
Internal Energy ◽  
Rate Constant ◽  
Molecular Ions ◽  
Energy Scale ◽  
Constant Density ◽  
Fragment Ions ◽  
Linear Threshold ◽  
Primary Fragmentation ◽  
Order Of Magnitude ◽  
Slow Rise

Differences between the appearance potentials of fragment ions formed a few μ secs after the ionization (so-called metastables) and normal fragment ions were measured. It is shown, however, that no immediate meaning regarding the primary fragmentation mechanism can be attached to these quantities. Instead, the experimental ionization curves of metastable and normal fragments were explained by a theoretical model which assumes 1) a linear threshold law, 2) a linear relation between the logarithm of the rate constant and the internal energy in the molecular ion, and 3) a constant density of populated states on the energy scale. In the case of HCN loss from benzonitrile ions, an excellent fit between the experimental and theoretical curves can then be achieved if it is assumed that an increase of 0.65 eV internal energy increases the rate constant by one order of magnitude. This is a surprisingly slow rise of k (E), compared with the few existing calculations in other cases.

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