Development of impurity seeding for divertor power flux handling in Wendelstein 7-X long pulse scenarios

• Main Authors: Effenberg, Florian, Barbui, T., Brezinsek, Sebastijan, Feng, Y., Frerichs, H., Geiger, J., Jakubowski, M., König, Ralf, Krychowiak, M., Lore, J.D., Naujoks, D, Niemann, H., Reimold, F., Schmitt, J.C., Schmitz, O., Pedersen, T. Sunn, Wurden, G.A., Zhang, D.
• Other Authors: Princeton Plasma Physics Laboratory (PPPL), Princeton University, Institute of Energy and Climate Research - Plasma Physics (IEK-4), Forschungszentrum Jülich GmbH, Helmholtz-Gemeinschaft = Helmholtz Association-Helmholtz-Gemeinschaft = Helmholtz Association, Max-Planck-Institut für Plasmaphysik Garching (IPP), University of Wisconsin-Madison, Max-Planck-Institut fur Plasmaphysik Teilinstitut Greifswald, Wendelsteinstr. 1, 17491 Greifswald, Germany, Oak Ridge National Laboratory Oak Ridge (ORNL), UT-Battelle, LLC, Auburn University (AU), Los Alamos National Laboratory (LANL)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2019
• Subjects: stellarator; w7-x; divertor; island divertor; impurity seeding; detachment; emc3-eirene; nuclear fusion; nuclear reactor; plasma; divertor d'île; ensemencement d'impuretés; détachement; fusion nucléaire; réacteur nucléaire; [PHYS.PHYS]Physics [physics]/Physics [physics]; [PHYS.NEXP]Physics [physics]/Nuclear Experiment [nucl-ex]; [PHYS.HIST]Physics [physics]/Physics archives; [SPI.PLASMA]Engineering Sciences [physics]/Plasmas; [PHYS.PHYS.PHYS-PLASM-PH]Physics [physics]/Physics [physics]/Plasma Physics [physics.plasm-ph]; [SPI]Engineering Sciences [physics]; [SPI.MAT]Engineering Sciences [physics]/Materials; Edge Island
• Online Access: https://hal.science/hal-03750211; https://hal.science/hal-03750211/document; https://hal.science/hal-03750211/file/ICFRM-2019-Poster-Florian-Effenberg.pdf

International audience The handling and mitigation of high power fluxes onto the 3D-shaped main plasma facing components (PFCs) is an issue of critical importance during future long-pulse operations at Wendelstein 7-X (W7-X). Unmitigated heat fluxes would exceed critical material limits of currently 8 MWm-2 in attached phases and during plasma start-up. Higher plasma pressure and the evolution of the toroidal net-currents change the edge magnetic field geometry, shifting and focusing the strike lines on weaker parts of the divertor, risking overloading and melting in specific scenarios. This restricts the operational and configurational space for long-pulse operation. To address these issues and reduce the peak power fluxes and increase the widths of the wetted area, methods of power spreading and power dissipation are currently being developed. A promising technique is radiative power exhaust with seeded impurities. Experiments with neon (Ne) and nitrogen (N2) seeding in the standard island divertor configuration have demonstrated that the island divertor allows for stable plasma operation at enhanced radiative power losses reducing the power fluxes to the divertors by ~70% at the expense of a maximum loss in energy confinement of DtE≈15%. To prepare for long-pulse plasma scenarios seeding experiments have also been performed in configurations mimicking the evolution of the toroidal net-currents and plasma equilibrium effects by carefully adjusting the vacuum magnetic fields. The results show that the edge island geometry strongly determines the power and impurity exhaust and may be carefully adjusted to optimize for more stable and safe high radiative divertor operation. The effects of the magnetic field and impurities on the peak power fluxes and power widths will be discussed. 3D transport modeling with EMC3-EIRENE is used to analyze these effects and resolve the underlying main transport features. In particular, impurity seeding will be discussed with respect to its aim and suitability of detachment ...