Presentation Magnetically-guided liquid metal divertor (MAGLIMD)

嶋田, 道也

Removal of extremely high heat load on the divertor poses the most challenging issue for DEMO design, and unmitigated ELMs and disruption will cause melting and subsequent deformation of target surfaces, raising a very serious concern for ITER and DEMO. Actively convected liquid metal divertor (ACLMD) was proposed to provide a solution to these two problems [1]. ACLMD employs liquid metal (LM) in place of solid divertor targets. Toroidal electrode(s) embedded in the LM would enable active convection induced by J x B force, where J is the current in the LM and B is the magnetic field. The active convection spreads the heat from the plasma deposited on narrow zones to a large volume/surface, significantly facilitating heat removal. After ELMs and disruption, LM will quickly recover a flat surface and heat removal capability. Proof-of-principle (PoP) experiments were carried out in NIFS, demonstrating that ACLMD also provides a means to pump particles in steady state [2].This paper proposes an innovative scheme of ACLMD, eliminating the need of electrodes in the LM. All needed are exhaust pipes of LM with their openings located near the separatrix hit point on the inboard bottom of the LM container, as well as LM supply tubes with their openings located near the separatrix hit point on the outboard bottom of the LM container. Other configurations will be also discussed.Since LM flow basically follows the field line, the LM volume that is directly connected to the exhaust opening along the field line will be exhausted, where the LM in the neighboring volume will flow in. The LM in the volume that is directly connected to the supply opening along the field line will flow out. Since the LM connected to the exhaust opening and the LM connected to the supply opening flow in the same direction, the whole LM will rotate toroidally due to viscosity, assuring uniformity along the toroidal direction even with a limited number of openings for LM supply and exhaust. Cross-field flow e.g. on the surface in the private region between the two divertor channels suffers from mhd drag, even if the wall is insulated to reduce the return current. However, a simple estimate of the mhd drag suggests that the mhd drag can be compensated for by a toroidally continuous step on the LM surface, only a few mm in height. A possible scheme of experiments in the QUEST device will be discussed.[1] Michiya Shimada and Yoshi Hirooka, Nuclear Fusion 54 (2014) 122002.[2] Yoshi Hirooka et al., “Hydrogen and helium recycling from a JxB-force convected liquid metal Ga67In20.5Sn12.5 under steady state plasma bombardment”, Fusion Engineering and Design 117 (2017) 140.
Joint meeting of 26th International Toki Conference and 11th Asia Plasma & Fusion Association Conference

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