Abstrakti
Erosion, transport and deposition of wall impurities are major concerns in future magnetic fusion devices, both from the perspective of the fusion plasma and the machine wall. An extensive study on molybdenum transport and deposition performed in the TEXTOR tokamak yielded a detailed deposition map that is ideal for benchmark deposition studies. A qualitative benchmark is attempted in this article with the ASCOT code. We set up a full 3D model of the TEXTOR tokamak and studied the influence of different physical mechanisms and their strengths on molybdenum deposition patterns on the simulated plasma-facing components: atomic processes, Coulomb collisions, scrape-off layer (SOL) profiles, source distribution, marker starting energy, radial electric field strength, SOL flow and toroidal plasma rotation. The outcome comprises 13 simulations, each with 100,000 markers. The findings are: • Toroidal plasma movement, either within the LCFS or as SOL flow, is negligible. • SOL profile and marker starting energy have modest impact on deposition. • Source distribution has a large impact in combination with radial electric field profiles. • The E⇀×B⇀ drift has the highest impact on the deposition profiles.
| Alkuperäiskieli | Englanti |
|---|---|
| Sivut | 307-315 |
| Sivumäärä | 9 |
| Julkaisu | Nuclear Materials and Energy |
| Vuosikerta | 19 |
| DOI - pysyväislinkit | |
| Tila | Julkaistu - 1 toukok. 2019 |
| OKM-julkaisutyyppi | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä |
Rahoitus
We used the TEXTOR MoF 6 marker experiment as a setting for extensive ASCOT simulations, studying the importance of various physical mechanisms. The following conclusions are drawn. • Toroidal plasma movement, either in central plasma due to NBI or in the SOL due to flow towards the PFCs, has very small influence on high-Z marker deposition. • The E ⇀ × B ⇀ drift is one of the most important parameters for global marker transport, and hence exact knowledge of radial electric field profiles is needed for proper impurity transport code benchmarking. • The source distribution is another important parameter, yet its impact on simulation results depends on the strength of the radial electric field. • Marker starting energy has a modest influence on deposition. For detailed studies one therefore needs to simulate also the dissociation of molecules. For rather coarse assessments, approximations might be feasible. • While changing the SOL profile does not change the qualitative picture, the deposition efficiencies are notably altered. Finally, when comparing the qualitative results with experimentally obtained results, see Fig. 8 , the closest match is obtained by Simulations (VI)–(VIII), albeit with three times too strong electric field. This illustrates that the closest match between experiment and simulation is not necessarily obtained by the most realistic set of simulation parameters. The most realistic set of parameters investigated in ASCOT was in Simulation case (X-b). Still, substantial features of the experimental deposition patterns could not be obtained: deposition on the ALT-II limiter next to the gas inlet, and deposition on top of the IBL. This indicates the importance of PWI effects neglected in the present ASCOT simulations, namely reflection and re-erosion. We therefore encourage benchmarking and parameter studies with other 3D codes including PWI processes, e.g. ERO 2.0. A cknowledgements This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under grant agreement no 633053 . The views and opinions expressed herein do not necessarily reflect those of the European Commission. The work was partially funded by the Academy of Finland project no. 298126 . All the simulations performed were carried out using the computer resources within the Aalto University School of Science ‘Science-IT’ project.