Active Radiative Liquid Lithium Diverto Concept
Authors: Masayuki Ono, et. al.
Abstract:
Developing a reactor compatible divertor has been identified as a particularly challenging technology problem
for magnetic confinement fusion. Application of lithium (Li) in NSTX resulted in improved H-mode confinement,
H-mode power threshold reduction, and reduction in the divertor peak heat flux while maintaining essentially
Li-free core plasma operation even during H-modes. These promising Li results in NSTX and related modeling
calculations motivated the radiative liquid lithium divertor (RLLD) concept [1]. In the RLLD, Li is evaporated
from the liquid lithium (LL) coated divertor strike point surface due to the intense heat flux. The evaporated Li is
readily ionized by the plasma due to its low ionization energy, and the poor Li particle confinement near the
divertor plate enables ionized Li ions to radiate strongly, resulting in a significant reduction in the divertor heat flux.
This radiative process has the desired effect of spreading the localized divertor heat load to the rest of the divertor
chamber wall surfaces, facilitating divertor heat removal. The modeling results indicated that the Li radiation can
be quite strong, so that only a small amount of Li (~ a few moles/sec) is needed to significantly reduce the divertor
peak heat flux for typical reactor parameters. In this paper, we examine an active version of the RLLD, which we
term ARLLD, where LL is injected in the upstream region of divertor. We find that the ARLLD has similar
effectiveness in reducing the divertor heat flux as the RLLD, again requiring only a few moles/sec of LL to
significantly reduce the divertor peak heat flux for a reactor. An advantage of the ARLLD is that one can inject
LL proactively even in a feedback mode to insure the divertor peak heat flux remains below an acceptable level,
providing the first line of defense against excessive divertor heat loads which could result in damage to divertor
PFCs. Moreover, the low confinement property of the divertor (i.e. < 1 ms for Li particle confinement time)
makes the ARLLD response fast enough to mitigate the effects of possible transient events such as large ELMs.
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Submitted to:
Fusion Engineering and Design (November 2013)
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Download PPPL-4964 (pdf 275 KB 8 pp)
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