Modelling tokamak power exhaust and scrape-off-layer thermal transport in high-power fusion devices

Managing the steady-state power loading onto the divertor target plates remains a major unresolved challenge facing tokamak fusion energy, that will be crucial for the success of the next generation of high-power reactor-level devices. This thesis will tackle two topics within this wide research area: assessing the performance of advanced divertor geometries in the context of the ARC reactor concept, and studying the impact of 'nonlocal' thermal transport on modelling predictions for the ITER tokamak SOL. Numerical simulations are performed using UEDGE for the Super-X divertor (SXD) and X-point target divertor (XPTD) configurations proposed for the ARC reactor design. The SXD, combined with 0.5% fixed-fraction neon impurity concentration, produced passively stable, detached divertor regimes for power exhausts in the range of 80-108 MW. The XPTD configuration is found to reduce the strike-point temperature by a factor of ~10 compared to the SXD for small X-point radial separations (~1.4lambda_{q||}). Even greater potential reductions are identified for separations of ≤1lambda_{q||}. Raising the separatrix density by a factor 1.5, stable detached divertor solutions were obtained that fully accommodate the ARC exhaust power without impurity seeding. In the presence of steep temperature gradients, classical local transport theory breaks down, and thermal transport becomes nonlocal, depending on conditions in distant regions of the plasma. An advanced nonlocal thermal transport model is implemented into the 'SD1D' complex SOL code to create 'SD1D-nonlocal', and applied to study typical ITER steady-state conditions. Results suggest that nonlocal transport effects will have importance for the ITER SOL, with discrepancies observed between nonlocal/local transport model predictions in low-density scenarios. Heat flux models employing global flux limiters are shown to be inadequate to capture the spatially/temporally changing SOL conditions. An analysis of SOL collisionality and nonlocality suggests nonlocal effects will be significant for future devices such as DEMO and ARC as well

MUSIC THERAPY ASSESSMENT: PSYCHOLOGICAL ASSESSMENT WITHOUT WORDS

Når klienter henvises til musikterapi, gennemgår de en assessment- procedure (en klinisk vurdering), som kræver terapeutens ekspertise inden for forskellige områder – med henblik på at stille en diagnose og identificere klientens behov og potentialer, samt at opstille realistiske forventninger til behandlingen. Inden for musikterapi findes der et antal publicerede assessment- metoder, som giver terapeuter mulighed for at anvende ikke-standardiserede redskaber såvel som målgruppe-specifikke metoder til at vurdere interventionens mulige effekt. Artiklen giver et koncentreret overblik over de vigtigste funktioner i musikterapeutisk assessment, og der gives eksempler på nogle af de metoder, der findes i musikterapilitteraturen. Et case-eksempel viser, hvordan børn med forstyrrelser inden for det autistiske spektrum vurderes med henblik på at afdække styrkesider, potentialer og ressourcer, som ellers muligvis forbliver skjult ved anvendelsen af andre, mere formaliserede assessment-metoder

Scaling laws for electron kinetic effects in tokamak scrape-off layer plasmas

Tokamak edge (scrape-off layer) plasmas can exhibit non-local transport in the direction parallel to the magnetic field due to steep temperature gradients. This effect along with its consequences has been explored at equilibrium for a range of conditions, from sheath-limited to detached, using the 1D kinetic electron code SOL-KiT, where the electrons are treated kinetically and compared to a self-consistent fluid model. Line-averaged suppression of the kinetic heat flux (compared to Spitzer-Harm) of up to 50% is observed, contrasting with up to 98% enhancement of the sheath heat transmission coefficient, $\gamma_e$. Simple scaling laws in terms of basic SOL parameters for both effects are presented. By implementing these scalings as corrections to the fluid model, we find good agreement with the kinetic model for target electron temperatures. It is found that the strongest kinetic effects in $\gamma_e$ are observed at low-intermediate collisionalities, and tend to increase at increasing upstream densities and temperatures. On the other hand, the heat flux suppression is found to increase monotonically as upstream collisionality decreases. The conditions simulated encompass collisionalities relevant to current and future tokamaks.Comment: 24 pages, 14 figure

Scaling laws for electron kinetic effects in tokamak scrape-off layer plasmas

Tokamak edge (scrape-off layer (SOL)) plasmas can exhibit non-local transport in the direction parallel to the magnetic field due to steep temperature gradients. This effect along with its consequences has been explored at equilibrium for a range of conditions, from sheath-limited to detached, using the 1D kinetic electron code SOL-KiT, where the electrons are treated kinetically and compared to a self-consistent fluid model. Line-averaged suppression of the kinetic heat flux (compared to Spitzer-Härm) of up to 50% is observed, contrasting with up to 98% enhancement of the sheath heat transmission coefficient, γe. Simple scaling laws in terms of basic SOL parameters for both effects are presented. By implementing these scalings as corrections to the fluid model, we find good agreement with the kinetic model for target electron temperatures. It is found that the strongest kinetic effects in γe are observed at low-intermediate collisionalities, and tend to increase (keeping upstream collisionality fixed) at increasing upstream densities and temperatures. On the other hand, the heat flux suppression is found to increase monotonically as upstream collisionality decreases. The conditions simulated encompass collisionalities relevant to current and future tokamaks

Effects of motifs in music therapy on the attention of children with externalizing behavior problems

Recent studies highlight the role of attention (i.e., executive attention and joint attention) in the negative association between children’s externalizing behavior problems (EBPs) and self-regulation. In music therapy improvisation, “Motifs” represent a repeated and meaningful use of freely improvised or structured music. They have been reported to be effective in drawing attention toward joint musical engagement. This study aimed to examine the effects of clinically derived motifs on the attention of a child with EBPs. Video microanalysis of four therapy sessions was employed. Interaction segments with/without motifs were then selected for analysis: (a) Executive attention measurement: a two-way analysis of variance (ANOVA) was conducted to examine the effects of Motifs (Factor I) across sessions (Factor II) on the duration of interaction segments. (b) Joint attention measurement: another two-way ANOVA investigated the effects of these two factors on the duration of joint attentive responses in each segment. Results showed that (a) the segments with Motifs tended to decrease in duration throughout the sessions, while (b) these segments showed a significant increase in proportions of joint attentional responses. These findings suggest a positive effect of Motifs on enhancing efficiency of joint attention execution over time, indicating the child’s recognition of the Motifs through learning

Cross-code comparison of the edge codes SOLPS-ITER, SOLEDGE2D and UEDGE in modelling a low-power scenario in the DTT

As reactor-level nuclear fusion experiments are approaching, a solution to the power exhaust issue in future fusion reactors is still missing. The maximum steady-state heat load that can be exhausted by the present technology is around 10 MW m-2. Different promising strategies aiming at successfully managing the power exhaust in reactor-relevant conditions such that the limit is not exceeded are under investigation, and will be tested in the Divertor Tokamak Test (DTT) experiment. Meanwhile, the design of tokamaks beyond the DTT, e.g. EU-DEMO/ARC, is progressing at a high pace. A strategy to work around the present lack of reactor-relevant data consists of exploiting modelling to reduce the uncertainty in the extrapolation in the design phase. Different simulation tools, with their own capabilities and limitations, can be employed for this purpose. In this work, we compare SOLPS-ITER, SOLEDGE2D and UEDGE, three state-of-the-art edge codes heavily used in power exhaust studies, in modelling the same DTT low-power, pure-deuterium, narrow heat-flux-width scenario. This simplified, although still reactor-relevant, testbed eases the cross-comparison and the interpretation of the code predictions, to identify areas where results differ and develop understanding of the underlying causes. Under the conditions investigated, the codes show encouraging agreement in terms of key parameters at both targets, including peak parallel heat flux (1%-45%), ion temperature (2%-19%), and inner target plasma density (1%-23%) when run with similar input. However, strong disagreement is observed for the remaining quantities, from 30% at outer mid-plane up to a factor 4-5 at the targets. The results primarily reflect limitations of the codes: the SOLPS-ITER plasma mesh not reaching the first wall, SOLEDGE2D not including ion-neutral temperature equilibration, and UEDGE enforcing a common ion-neutral temperature. Potential improvements that could help enhance the accuracy of the code models for future applications are also discussed