Speaker
Description
The difficulties with solid divertors for power handling in future reactors have long been recognized. In response to this challenge, the US initiated research into liquid metals as an alternative under the Advanced Power Extraction (APEX) program.[1] To study the behavior of liquid metals with a large free surface in the presence of tokamak fields, a fully-toroidal Liquid Lithium Limiter (LLL) was installed in the Current Drive Experiment-Upgrade (CDX-U) spherical tokamak.[2] The LLL was subject to high local heating with an electron beam, and convection in the liquid lithium was observed to distribute the heat load.[3] The explanation was found to be thermoelectric magnetohydrodynamics (TEMHD),[4] and is the principle behind the Liquid Metal Infused Trench (LiMIT) system being implemented as a limiter on the EAST tokamak.[5] Lithium as a divertor target was also explored in the National Spherical Torus Experiment (NSTX) device, both as a coating on graphite plasma-facing components and a fully-toroidal Liquid Lithium Divertor (LLD).[6] These approaches have addressed issues of particle control with lithium coatings and the stability of a liquid lithium layer on the textured LLD substrate.[7] An additional effect that needs to be considered is ablation from the lithium surface under high heat loads. If the divertor is constructed with a box-like geometry, it could enable the lithium vapor to reach a sufficiently high density to extract momentum and energy from divertor plasmas.[8] A prototype consisting of “vapor boxes” (VBs) attached together is being used to see if the configuration can separate the high pressure of lithium vapor from an outer vacuum chamber. For simplicity, the VBs are a series of cylinders that can be individually heated. If successful, the VBs can be tested with plasmas on the Magnum-PSI linear divertor simulator. Research in liquid metals to address specific engineering problems has thus uncovered new and unexpected phenomena, and broadened the options for their implementation in future divertors.
*Work supported by USDOE Contract DE-AC02-09CH11466.
[1] M. Abdou et al., Fusion Eng. Design 54, 181 (2001)
[2] R. Majeski et al., Phys. Rev. Letters 97, 075002 (2006)
[3] R. Kaita et al., Phys. Plasmas, 14, 056111 (2007)
[4] M. Jaworski et al., Phys. Rev. Letters 104, 094503 (2010)
[5] D. Ruzic et al., Nucl. Fusion 21, 102002 (2011)
[6] H. Kugel et al., Fusion Eng. Design 87, 1724–1731 (2012)
[7] M. Jaworski et al., Plasma Phys. Control. Fusion 55, 124040 (2013)
[8] R. Goldston et al., Phys. Scripta T167, 014017 (2015)
| Eligible for student paper award? | No |
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