The new ASDEX upgrade upper divertor for special alternative configurations: Design and FEM calculations

• Published in: Fusion engineering and design 2021-10, Vol.171, p.112468, Article 112468
• Main Authors: Zammuto, I., Weißgerber, M., Herrmann, A., Dibon, M., Rohde, V., Schall, G., Teschke, M., Vierle, T., Vorbrugg, S.
• Format: Article
• Language: English
• Subjects: ASDEX Upgrade; Conductors; Configuration management; Cryopumping; Divertors (fusion reactors); Field coils; Finite element method; In-vessel coil; Mathematical models; Prototyping; Snow-flake divertor; Tokamak devices
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2021.112468

ASDEX Upgrade (AUG) is the experimental tokamak based in Germany that since many years, 1991, explores technical solutions to address physic aspects. This time, the aim is to prove that alternative divertor configurations (X-divertor or Snowflake divertor) can mitigate the power exhaust problem, in a machine with high heating power like AUG. To realize the required magnetic configurations [2], two poloidal field coils are required in the divertor region. The upgrade in AUG will be carried out in the upper divertor and the following components will be newly designed and installed in the next years: cryopump, inner and outer divertors and finally two divertor coils [4]. In the design phase, many challenges were faced: 1) Manufacturing and qualification of a conductor able to safely operate the coils [6]; 2) Implementation of the new components in a tight room, maintaining the plasma volume and the present plasma configurations; 3) Implementation of the divertor coils close to the strike line. The design has reached a certain level of maturity and a prototyping phase has been started. The installation of the component is planned for 2022 and at that time AUG will be the first tokamak having in-situ winded coils. The components design is based on the experience gained in years of AUG operation, which allowed for the building up of an extensive database to get the input parameters for the FEM analyses. Induced and halo currents interacting with the static toroidal field are the main source of loads in the structure. Different electromagnetic models were prepared to address the problem together with their corresponding mechanical models. The design has been iteratively changing according to the results of the FEM analyses. The paper will present the design of the upper divertor components and the analyses carried out to verify their mechanical integrity.