Multi‐fluid code simulation of DIII‐D filterscope data including reflection of light from plasma‐facing surfaces (original) (raw)
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Interpretive modeling of simple-as-possible-plasma discharges on DIII-D using the OEDGE code
Journal of Nuclear Materials, 2003
Recently a number of major, unanticipated effects have been reported in tokamak edge research raising the question of whether we understand the controlling physics of the edge. This report is on the first part-here focused on the outer divertor-of a systematic study of the simplest possible edge plasma-no ELMs, no detachment, etc.-for a set of 10 repeat, highlydiagnosed, single-null, divertor discharges in DIII-D. For almost the entire, extensive data set so far evaluated, the matches of experiment and model are so close as to imply that the controlling processes at the outer divertor for these simple plasma conditions have probably been correctly identified and quantitatively characterized in the model. The principal anomaly flagged so far relates to measurements of T e near the target, potentially pointing to a deficiency in our understanding of sheath physics in the tokamak environment.
Journal of Nuclear Materials, 2015
A discrepancy in the divertor radiated powers between EDGE2D-EIRENE simulations, both with and without drifts, and JET-ILW experiments employing a set of NBI-heated L-mode discharges with step-wise density variation is investigated. Results from a VUV/visible poloidally scanning spectrometer are used together with bolometric measurements to determine the radiated power and its composition. The analysis shows the importance of D line radiation in contributing to the divertor radiated power, while contributions from D radiative recombination are smaller than expected. Simulations with W divertor plates underestimate the Be content in the divertor, since no allowance is made for Be previously deposited on the plates being re-eroded. An improved version of EDGE2D-EIRENE is used to test the importance of the deposited layer in which the sputtering yield from supposed pure Be divertor plates is reduced to match the spectroscopic signals, while keeping the sputtering yield for the Be main chamber walls unchanged.
Comprehensive 2D measurements of radiative divertor plasmas in DIII-D
Journal of Nuclear Materials, 1997
This paper presents a comparison of the total radiated power profile and impurity line emission distributions in the SOL and divertor of DIII-D. This is done for ELMing H-mode plasmas with heavy deuterium injection (Partially Detached Divertor operation, PDD) and those without deuterium puffing. Results are described from a series of dedicated experiments performed on DIII-D to systematically measure the 2-D (R,Z) structure of the divertor plasma. The discharges were designed to optimize measurements with new divertor diagnostics including a divertor Thomson scattering system. Discharge sequences were designed to produce optimized data sets against which SOL and divertor theories and simulation codes could be benchmarked. During PDD operation the regions of significant radiated power shift from the inner divertor leg and SOL to the outer leg and X-point regions. Da emission shifts from the inner strikepoint to the outer strikepoint. Carbon emissions (visible CII and CIII) shift from the inner SOL near the X-point to a distributed region from the X-point to partially down the outer leg during moderate D2 puffing. In heavy puffing discharges the carbon emission coalesces on the outer separatrix near the X-point and for very heavy puffing it appears inside the last closed flux surface above the X-point. Calibrated spectroscopic measurements indicate that hydrogenic and carbon radiation can account for all of the radiated power. La and CIV radiation are comparable and when combined account for as much as 90% of the total radiated power along chords viewing the significant radiating regions of the outer leg.
Validation of numerical codes for the analysis of plasma discharges
Fusion Engineering and Design, 1994
Electromagnetic aspects in the design of ITER-like reactors call for an extensive use of complex and advanced numerical codes. For this reason a strong attention has been paid within the NET-Team to the code development. In particular, through a cooperation with some Italian universities, during the last years a number of numerical procedures were developed and integrated. In order to assess the code reliability and to gain confidence on their predictions for next generation ITER-like reactors, the validation of the codes against experiments has to be considered as a strict requirement. Aim of this paper is to give a comprehensive presentation of this problem in the light of the results of a campaign of validation runs. The main outcome of this work is that the computational procedures, which have been developed for the NET project and then extensively used also for ITER studies, can be considered as experimentally validated in a sufficiently wide range of cases of interest. In particular, computed values are compared with experimental measurements made during some typical ASDEX-Upgrade discharges. From the electromagnetic point of view, many features of this machine are common to the ITER concept, so that the results of the validation can reasonably be extended to the ITER case.
Radiative Divertor Plasma Behavior in L- and H-Mode Discharges with Argon Injection in EAST
Plasma Science and Technology, 2013
Introducing strong radiative impurities into divertor plasmas has been considered as an important way to mitigate the peak heat load at the divertor target plate for ITER, and will be employed in EAST for high power long pulse operations. To this end, radiative divertor experiments were explored under both low (L) and high (H)-mode confinement regimes, for the first time in EAST, with the injection of argon and its mixture (25% Ar in D2). The Ar injection greatly reduced particle and heat fluxes to the divertor in L-mode discharges, achieving nearly complete detached divertor plasma regimes for both single null (SN) and double null (DN) configurations, without increasing the core impurity content. In particular, the peak heat flux was reduced by a factor of ∼6, significantly reducing the intrinsic in-out divertor asymmetry for DN, as seen by both the new infra-red camera and the Langmuir probes at the divertor target. Promising results have also been obtained in the H-modes with argon seeding, demonstrating a significant increase in the frequency and decrease in the amplitude of the edge localized modes (ELMs), thus reducing both particle and heat loads caused by the ELMs. This will be further explored in the next experimental campaign with increasing heating power for long pulse operations.
1D Fluid Model of Plasma Profiles in the LHD Divertor Leg
One dimensional plasma model of the divertor leg in Large Helical Device is presented. The plasma is described by stationary fluid equations for electron and ion with particle source by ionization and momentum sink by charge exchange with neutrals. Also a simple model of neutral atoms and radiative cooling by impurities are included. This model is intended to be employed in an integrated simulation where an equilibrium of the upstream plasma and plasma-surface interactions at the divertor plate are solved in different numerical codes separately. From the computational point of view, the numerical code solving the fluid equations for the divertor leg is developed for 1D flux tube where the boundary conditions of both ends are specified. The calculation time is much less than 0.1 seconds and sufficiently fast to use in future integrated simulations. Solutions for typical plasma parameters are shown in the paper. In the results, a density peaking near the wall was observed for the plasma of high density. The peaking is caused by the ion heat conduction and the collisional presheath and its sharpness increases for higher density. Also solutions for different impurity density profiles were obtained and reduction of the electron energy flux and temperature were observed. However, their effects were small and qualitative changes were not observed.
Divertor plasma studies on DIII-D: experiment and modelling
Plasma Physics and Controlled Fusion, 1997
In a magnetically diverted tokamak, the scrape-off layer (SOL) and divertor plasma provides separation between the first wall and the core plasma, intercepting impurities generated at the wall before they reach the core plasma. The divertor plasma can also serve to spread the heat and particle flux over a large area of divertor structure wall using impurity radiation and neutral charge exchange, thus reducing peak heat and particle fluxes at the divertor strike plate. Such a reduction will be required in the next generation of tokamaks, for without it, the divertor engineering requirements are very demanding. To successfully demonstrate a radiative divertor, a highly radiative condition with significant volume recombination must be achieved in the divertor, while maintaining a low impurity content in the core plasma.
Discharge Plasma Influence on Flow Characteristics Near Wall Step in a High-Speed Duct
At the present time numbers of theoretical and experimental works have been published, which show that energy release to airflow near/fore streamlined bodies can reduce a total drag of these bodies. It occurs at high level of energetic efficiency (sometimes, much more than 1) . Several works are described efforts in a field of plasma influence on a viscous friction and separation zone properties . As was shown by last investigations an energetic method of boundary layer control (volume energy release to gas near surface by means of electrical discharge) leads to non-trivial response. Wall steps and cavities are offered as a constructive element in supersonic combustors. Such an element can provide an artificial separation zone for a flame front stabilization and a fuel-air mixture burning initiation. Last time a plasma assisted combustion technology is discussed for purpose of a high-speed combustor development .
Analysis of pedestal plasma transport
Nuclear Fusion, 2010
An H-mode edge pedestal plasma transport benchmarking exercise was undertaken for a single DIII-D pedestal. Transport modelling codes used include 1.5D interpretive (ONETWO, GTEDGE), 1.5D predictive (ASTRA) and 2D ones (SOLPS, UEDGE). The particular DIII-D discharge considered is 98889, which has a typical low density pedestal. Profiles for the edge plasma are obtained from Thomson and charge-exchange recombination data averaged over the last 20% of the average 33.53 ms repetition time between type I edge localized modes. The modelled density of recycled neutrals is largest in the divertor X-point region and causes the edge plasma source rate to vary by a factor ∼10 2 on the separatrix. Modelled poloidal variations in the densities and temperatures on flux surfaces are small on all flux surfaces up to within about 2.6 mm (ρ N > 0.99) of the mid-plane separatrix. For the assumed Fick's-diffusion-type laws, the radial heat and density fluxes vary poloidally by factors of 2-3 in the pedestal region; they are largest on the outboard mid-plane where flux surfaces are compressed and local radial gradients are largest. Convective heat flows are found to be small fractions of the electron ( 10%) and ion ( 25%) heat flows in this pedestal. Appropriately averaging the transport fluxes yields interpretive 1.5D effective diffusivities that are smallest near the mid-point of the pedestal. Their 'transport barrier' minima are about 0.3 (electron heat), 0.15 (ion heat) and 0.035 (density) m 2 s −1 . Electron heat transport is found to be best characterized by electron-temperaturegradient-induced transport at the pedestal top and paleoclassical transport throughout the pedestal. The effective ion heat diffusivity in the pedestal has a different profile from the neoclassical prediction and may be smaller than it. The very small effective density diffusivity may be the result of an inward pinch flow nearly balancing a diffusive outward radial density flux. The inward ion pinch velocity and density diffusion coefficient are determined by a new interpretive analysis technique that uses information from the force balance (momentum conservation) equations; the paleoclassical transport model provides a plausible explanation of these new results. Finally, the measurements and additional modelling needed to facilitate better pedestal plasma transport modelling are discussed.