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Kukushkin, A. S.

Publications and source records attributed to Kukushkin, A. S..

12 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

1D model of tokamak scrape-off layer and divertor plasmas: Dimensionless parameters and the results of numerical simulations

Solutions of a 1D model of the scrape-off layer and a divertor plasma in a tokamak are analyzed on the basis of dimensionless parameters governing the physics of both plasma and neutral transport and atomic physics processes. Numerical simulations based on fluid plasma and Monte Carlo neutral modeling confirm earlier results obtained with simplified analytic considerations and numerical simulations performed with fluid neutral description and demonstrate bifurcation of plasma parameters. Further, these simulations also confirm that the major physical reasons for the rollover of the plasma flux to the target, which is the key feature of the phenomenon of divertor plasma detachment, are the impurity radiation loss and plasma recombination. It is suggested that simulations of the edge plasma based on dimensionless parameters provide a powerful tool for checking the consistency of the physics incorporated in existing complex 2D codes used for edge plasma modeling.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Bifurcations and oscillations in divertor plasma

Here a qualitative picture of development of a bifurcated plasma state in a single-null and double-null divertor configurations is discussed. The simple analytical considerations are verified with SOLPS code modeling in quasi-1D setup. In a more realistic, 2D model, these bifurcations cause self-sustained oscillations of the plasma parameters, leading to deep modulation of the power loading on the divertor targets. In the symmetric double-null case, the bifurcations prompt a spontaneous loss of the up-down symmetry, which results in a sharp, counter-intuitive increase of the power loading on one of the targets along with an increase of the particle content in the divertor plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2018

SOLPS4.3 Modeling of Lithium Transport and Noncoronal Radiation in the T-15 Tokamak with Lithium Emitter−Collector Scheme in Use

The lithium emitter−collector scheme has been successfully used on limiter tokamak T-11M for a long time and is therefore one of the most mature concepts of liquid lithium-assisted power and particle exhaust. In the present paper, a possible application of the emitter−collector scheme to the divertor tokamak T-15 is analyzed with the 2D transport code SOLPS4.3. Modeling indicates that placing the lithium limiter at the outer midplane of the vessel results in the widest possible spreading of lithium over the scrape-off layer, whereas lithium deposition in this case is localized primarily at the upper outer target plate. The power exhaust capability of the lithium emitter−collector scheme is also studied. It is often presumed on the basis of a simple 0D analysis that the noncoronality can bring the lithium radiation capability in line with the other low-Z impurities typically involved in the divertor power exhaust (such as carbon and nitrogen). However, detailed 2D modeling shows that in spite of the significant increase of the Li cooling rate due to the noncoronal effects, the contribution of lithium radiation to divertor power balance remains marginal, unless the lithium inventory in the edge becomes close to the deuterium one.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Physics of ultimate detachment of a tokamak divertor plasma

The basic physics of the processes playing the most important role in divertor plasma detachment is reviewed. The models used in the two-dimensional edge plasma transport codes that are widely used to address different issues of the edge plasma physics and to simulate the experimental data, as well as the numerical schemes and convergence issues, are described. The processes leading to ultimate divertor plasma detachment, the transition to and the stability of the detached regime, as well as the impact of the magnetic configuration and divertor geometry on detachment, are considered. A consistent, integral physical picture of ultimate detachment of a tokamak divertor plasma is developed.

Physics↗
DOE OSTI2017

On detachment asymmetry and stability

Three issues related to the physics of divertor detachment are analyzed in detail: the criteria for the onset of complete divertor detachment, the role of neutrals in “symmetryzation” of detachment in the inner and outer divertors, and the transition to divertor detachment. The results of comprehensive 2D numerical simulations with the SOLPS4.3 package are compared with some experimental data and predictions based on simplified analytical models. It is shown that it is the ratio of the upstream plasma pressure to the specific power flux entering the recycling region that controls the local onset of detachment on a specific flux tube. P up /q reclycl ≥(P up /q reclycl ) crit remains the valid criterion also in the presence of seeded impurity, if the impurity radiation and hydrogen recycling regions are spatially separated. Detailed analysis indicates that the reverse plasma flow forming on the most heat loaded flux tubes in the outer divertor under the influence of the neutrals coming from the deeply detached inner divertor plays the key role in the detachment “symmetryzation” and allows the outer divertor to reach the detached regime. Finally, it is demonstrated that a gradual increase of the perpendicular heat transport in the edge plasma during transition to the detached regime can make this transition bifurcation-like.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2017

Stability of divertor detachment

The 2D simulations of edge plasma transport show that unlike some earlier publications, the impurity radiation loss per se does not cause the bifurcation-like transition to detached divertor regime. However, for the case where anomalous plasma transport is increasing with advancement to detachment, like it was recently observed experimentally, the transition to detachment exhibit the bifurcation-like character. Some other plausible reasons for similar bifurcation-like evolution to detachment are discussed. It is demonstrated that the current convective instability can be triggered in detached inner divertor plasma for the condition when outer divertor is still attached. This can explain the fluctuations of radiation loss observed recently experimentally for similar conditions. The self-sustained oscillations observed recently in numerical simulations and related to the interplay of the thermal force effects in impurity transport and impurity radiation loss are further investigated. It is shown that for some conditions these oscillations are ubiquitous, since no stable solutions possible.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Divertor plasma detachment

Regime with the plasma detached from the divertor targets (detached divertor regime) is a natural continuation of the high recycling conditions to higher density and stronger impurity radiation loss. Both the theoretical considerations and experimental data show clearly that the increase of the impurity radiation loss and volumetric plasma recombination causes the rollover of the plasma flux to the target when the density increases, which is the manifestation of detachment. Plasma-neutral friction (neutral viscosity effects), although important for the sustainment of high density/pressure plasma upstream and providing the conditions for efficient recombination and power loss, is not directly involved in the reduction of the plasma flux to the targets. The stability of detachment is also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Impurity-induced divertor plasma oscillations

Two different oscillatory plasma regimes induced by seeding the plasma with high- and low-Z impurities are found for ITER-like divertor plasmas, using computer modeling with the DUSTT/UEDGE and SOLPS4.3 plasma-impurity transport codes. The oscillations are characterized by significant variations of the impurity-radiated power and of the peak heat load on the divertor targets. Qualitative analysis of the divertor plasma oscillations reveals different mechanisms driving the oscillations in the cases of high- and low-Z impurity seeding. The oscillations caused by the high-Z impurities are excited near the X-point by an impurity-related instability of the radiation-condensation type, accompanied by parallel impurity ion transport affected by the thermal and plasma friction forces. The driving mechanism of the oscillations induced by the low-Z impurities is related to the cross-field transport of the impurity atoms, causing alteration between the high and low plasma temperature regimes in the plasma recycling region near the divertor targets. The implications of the impurity-induced plasma oscillations for divertor operation in the next generation tokamaks are also discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗