Power and momentum removal in the Scrape-Off Layer of ASDEX Upgrade

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School of Science | Doctoral thesis (article-based) | Defence date: 2021-02-05
Degree programme
100 + app. 30
Aalto University publication series DOCTORAL DISSERTATIONS, 10/2021
Dedicated experiments in ASDEX Upgrade (AUG) and interpretative studies of these experiments with the edge fluid code SOLPS have been carried out to investigate the relative importance of underlying physical processes of divertor transport and exhaust of momentum and power in tokamak plasmas in AUG. Analysis of pressure conservation in AUG H-mode plasmas shows that, at low electron target temperatures, the momentum losses in the scrape-off layer (SOL) near the separatrix are up to two orders of magnitude stronger compared to the momentum losses in the far SOL in flux tubes with the same target temperature. In L-mode-like and H-mode-like SOLPS 5.0 simulations, the momentum losses are up to two orders of magnitude weaker than experimentally observed at target temperatures below Te,t < 5 eV, and the dependence of the losses on the distance to the separatrix of the flux tube is only significant in the vicinity the separatrix. The L-mode-like simulations show that the impact of ion-atom charge-exchange on momentum transfer is larger than the impact of ion-molecule elastic scattering for the range of temperatures and plasma conditions observed in the SOL of AUG. Experiments and SOLPS-ITER simulations of the upper open divertor in AUG show that the net effect of increasing the core plasma density or the plasma current on the heat loads onto the targets strongly depends on the toroidal field direction. Within experimental and computational uncertainties, SOLPS-ITER predicted trends of the peak heat flux density at the targets with increasing core plasma density and plasma current are in quantitative agreement with the experimental data. Within the divertor region, these simulations show that the radial energy transport due to cross-field drifts is the primary component of the total radial transport contribution to energy transport. In L-mode-like simulations, the neutral model, the divertor closure, the boundary conditions and the SOLPS version do not significantly impact the target to upstream ratio of the total plasma pressure, ptot, t/ptot, u within the outer divertor, except for low temperatures (Te,t < 3 eV) in the vicinity of the separatrix. In the vicinity of the separatrix, drifts have a stronger impact on plasma momentum losses than the neutral model and divertor closure.
Supervising professor
Groth, Mathias, Prof., Aalto University, Department of Applied Physics, Finland
Thesis advisor
Wischmeier, Marco, Dr., Max Planck Institute for Plasma Physics, Germany
Scarabosio, Andrea, Dr., Max Planck Institute for Plasma Physics, Germany
plasma, fusion, tokamak, ASDEX Upgrade, SOLPS
Other note
  • [Publication 1]: I. Paradela Pérez, A. Scarabosio, M. Groth, M. Wischmeier, F. Reimold, ASDEX Upgrade Team. SOL parallel momentum loss in ASDEX Upgrade and comparison with SOLPS. Nuclear Materials and Energy, 12, 181–186, 2017.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201705114122
    DOI: 10.1016/j.nme.2017.01.026 View at publisher
  • [Publication 2]: I. Paradela Pérez, M. Groth, M. Wischmeier, A. Scarabosio, D. Brida, P. David, D. Silvagni, D. Coster, T. Lunt, M. Faitsch, the ASDEX-Upgrade Team, the EUROfusion MST1 Team. Assessment of particle and heat loads to the upper open divertor in ASDEX Upgrade in favourable and unfavourable toroidal magnetic field directions. Nuclear Materials and Energy, 19, 531–536, 2019.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-201906033333
    DOI: 10.1016/j.nme.2019.03.024 View at publisher
  • [Publication 3]: I. Paradela Pérez, M. Groth, M. Wischmeier, D. Coster, D. Brida, P. David, D. Silvagni, M. Faitsch, the ASDEX-Upgrade Team, the EUROfusion MST1 Team. Impact of drifts in the ASDEX Upgrade upper open divertor using SOLPS-ITER. Contributions to Plasma Physics, 4, e201900166, 2020.
    Full text in Acris/Aaltodoc: http://urn.fi/URN:NBN:fi:aalto-202004282848
    DOI: 10.1002/ctpp.201900166 View at publisher