Brida, D.

Conway, G.

Dux, R.

Gil, L.

Hachmeister, D.

Kurzan, B.

McDermott, R.

Santos, J.

Silva, A.

Silva, C.

Stroth, U.

Vicente, J.

Wolfrum, E.

English

MPG.PuRe

Inner-outer midplane density asymmetries and the link to the HFSHDclose to double null at ASDEX UpgradeD. Hachmeister1, C. Silva1, J. Santos1, G. D. Conway2, L. Gil1, A. Silva1, U. Stroth2,3, J. Vicente1, E.Wolfrum2, R. M. McDermott2, R. Dux2, B. Kurzan2, D. Brida2, and the ASDEX Upgrade Team1Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico, Universidade de Lisboa, Portugal2Max-Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748 Garching, Germany3Physik-Department E28, Technische Universität München, 85747 Garching, GermanyResearch at ASDEX Upgrade (AUG) has reported the formation of a high-field side high density(HFSHD) front in the divertor region associated with the inner divertor detachment [1]. The dynamicsof the midplane edge electron density profiles and its link to divertor detachment have been previouslystudied on AUG, taking advantage of the high-resolution HFS/LFS O-mode reflectometry diagnostic[2]. It has been shown that the formation of a high-density region in the midplane in front of the innerwall leads to strong poloidal asymmetries in the scrape-off layer density [2]. Building on these results,this work details the divertor detachment and HFSHD formation in highly shaped plasmas - close todouble null (DN) configuration - characteristic of many reactor concepts.For this purpose, we performed plasma configuration scans from lower single null (LSN) toupper single null (USN) passing through DN configuration. These scans were performed in both L- andH-mode at different fuelling and seeding levels to vary the detachment state and overall plasma density.During the transition from LSN to USN, we measured: (i) the inner and outer divertor density andtemperature using Thomson scattering and stark broadening spectroscopy; (ii) the target density andtemperature using Langmuir probes; (iii) the scrape-off layer density at the inner and outer midplaneusing O-mode reflectometry. These measurements allowed us to monitor the detachment state and themagnitude and location of the HFSHD during the LSN to USN transition.While moving from LSN to DN, the HFSHD moves from the far-SOL to the X-point region asthe HFSHD becomes increasingly disconnected from the LFS. Interestingly, the HFS density evenincreases when approaching DN despite the reduced magnetic connection to the LFS. In the midplanescrape-off layer, the LFS density experiences little change going from LSN to USN, but the HFSdensity - dominated by the midplane HFSHD front - is significantly lower in the USN case. Thishighlights the importance of the ExB drift in the divertor in establishing the HFS density since the driftpoints inwards in LSN and outwards in USN [3].[1] S. Potzel et al., Nuclear Fusion 54 (2014) 013001.[2] L. Guimarãis et al., Nuclear Fusion 59 (2019) 126041.[3] A. W. Leonard, Plasma Physics and Controlled Fusion, 60(4) (2018), 044001.48th EPS Conference on Plasma Physics P1a.119

Inner-outer midplane density asymmetries and the link to the HFSHD close to double null at ASDEX Upgrade

http://hdl.handle.net/21.11116/0000-000C-16D2-E

Inner-outer midplane density asymmetries and the link to the HFSHD close to double null at ASDEX Upgrade

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MPG.PuRe