Observations of wall conditioning by means of boron powder injection in DIII-D H-mode plasmas
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Author(s)
Bortolon, A.
Maingi, R.
Nagy, A.
Ren, J.
Duran, J.D.
Maan, A.
Donovan, D.C.
Boedo, J.A.
Rudakov, D.L.
Hyatt, A.W.
Date Issued
March 2020
Journal
Nuclear Fusion
Publisher
IOP
Abstract
We report observations from the DIII-D tokamak indicating that boron (B) powder injection in tokamak plasmas improves wall conditions similarly to glow discharge boronization (GDB). Isotopically enriched B powder (B11 > 95%) was introduced gravitationally in a sequence of H-mode plasma discharges at rates up to ∼160 mg s−1 for durations up to 3 s. Boron injection to cumulative amounts ≤0.1 g appeared to improve wall conditions similarly to boronization, with indications of reduced wall fueling, reduced recycling at the outer strike point and reduced impurity content at breakdown. Post-mortem analysis of graphite samples exposed to far scrape-off layer plasma fluxes during boron injection confirm the formation of a B-C layer, with average surface composition B:C ∼ 1. The results suggest that injecting boron-rich powders in tokamak plasmas can effectively replenish boron films on carbon plasma facing components to improve wall conditions and extend the duration of the beneficial effects of GDB.
Description
Submitted for publication in Nuclear Fusion
MIT Department
Massachusetts Institute of Technology. Plasma Science and Fusion Center
Persistent DSpace Link
DOI of Published Version
https://doi.org/10.1088/1741-4326/abaf31
